KITE SAILING.

 BY PETER LYNN VERSION 1999.

  WHY?

                      Because it's fun!

I love buggying, kitesurfing, single line kites and sitting on aeroplanes for days- of course I do!  For one thing, Elwyn wouldn't want me hanging around the house under her feet all the time.  For another, alternating spells of frantic activity amongst a bunch of nutters (kite events) then typically 2 days of being confined to seat 36a with nothing to do except think (sometimes with a dr), seems to be good for creativity.

But I confess, the kite activity I really like, the only one I consistently do just for myself even when there is no commercial or show-off element, is kitesailing. 

Just leaning back there in perfect wind sliding down one swell and up the other, sometimes on one tack just about forever (or so it seems), is a most enjoyable sensation.

But after 12 years and more effort than I've ever applied to any other project in my life trying to turn the world on to kite boats, the faithful are few. 

There are converts for a while but then they go back to buggying or take up kitesurfing, mere schisms of the true faith to my thinking. 

Even one of the first disciples, Nop Valthuizen (author, with Servaas van der Horst of the ever popular "Stunt Kites 1" and "2" and the soon to be published "Ugly kites 1") is backsliding.  Last month I left him alone for just a couple of weeks (having to go back to NZ for some quality time with the cats) and returned to find the boats in storage and Nop out trying to balance on this narrow pointy little kitesurfing board- simultaneous physical and spiritual wobbling.  Fortunately for his soul, I was able to get to him before the cock crowed three times.

The problem is not really function, kitesailing is now relatively easy and reliable, but for all the years of investment in research, design, development, manufacturing and marketing, our main kitesailing product, the monohull kiteboat, continues to be outsold by buggies about 100 to 1- and has already been outgrown by its younger sibling, kitesurfing.

The problem is that kite sailing lacks the excitement, speed, tricks, violence even of buggying and kitesurfing- and that kite boats are comparatively bigger/pricier. 

But wait a moment, yachts are bigger, slower, and vastly more expensive than any conceivable kiteboat- and hold more enthusiasts in their thrall than kite traction can even dream of. 

So what is wrong?

Like any obsessive true believer puzzled as to why everyone else doesn't share my passion, the answer has become clear.   There is something fundamentally wrong with them. 

Of course, this view may be just a little extreme, a more charitable explanation could be that proselytising takes time, that the one true faith will inevitably prevail in the fullness of time.

So, here and now, while wind remains, I recommit to fighting the good fight, through scorn, calms, storms, ice encrusted shore lines, and no matter how many holes there are in my wet suit nor times the lines wrap inextricably around the rudders while far from safe haven.

Maybe this review will save others from going down some of the blind alleys I've tried, but probably not- and maybe some of these paths will lead to somewhere next time anyway.

At least its a good way to organise my thinking in preparation for the summer campaigning- and it's snowing here so I certainly need an excuse to stay inside until going back north next week.

Perhaps it will spark enough interest to find homes for some of the junk (that is, prototypes) decorating the long grass out the back, which won't please the old chooks that roost on them but will please her indoors.

TERMINOLOGY

But first there is some terminology to define: more for the reason of getting key words in here somewhere to hook some net surfers.

Although some use KITE SAILING as a generic term for all KITE TRACTION activities , I will use KITE SAILING in its more common definition as "yachting using a kite as the sail". 

Boats for kitesailing are KITE BOATS.

BUGGYING is that KITE TRACTION activity in which the flier is sitting down on some type of wheeled vehicle.  BUGGYING is sometimes called PARAKARTING but this was an alternative name generated for commercial differentiation in the early 90's and is not as established. 

KITE SKIING is a confusing word as it can be referring to the use of snow skis or water skis.  As kite water skiing activity fades with the rising popularity of KITE SURFING, I suspect KITE SKIING will come to apply only to kite snow skiing but until then I will indicate which is meant.

KITESURFING is a general name for KITE TRACTION on the water using surfboard, windsurfer,  wakeboard or (single) water ski derived boards.

FLYSURFING (sounds like some type of fishing) is an alternative name for KITE SURFING.  Which will become dominant is not yet clear.

POWERKITING is sometimes used as a synonym for KITE TRACTION but as it includes KITE JUMPING, TETHERED FLYING and other unsavoury activities, KITE TRACTION should more properly be considered as a subset of POWER KITING.

With time it is likely that most of these terms will be used in their one word form:

KITESAILING, KITEBOATS, KITESURFING, FLYSURFING, KITESKIING, POWERKITING and KITETRACTION.

                                    NOW,

WHAT IS KITESAILING?

As from the definition above it's yachting with a kite, (a proper one, not a spinnaker), but that's very general and includes some less than entirely kosher activities.

For this discussion, kite sailing is not about using kites to pull around boats that were built for some other purpose, nor is it about using kites that were built for some non-traction purpose.

It's true that kites can be used to pull conventional yachts, I've done a bit of this myself as a quick test for this or that.  It's even true that single line kites have been used to pull boats along- Samuel Franklin Cody made it across the English Channel this way in 1903 and somebody went across the Atlantic similarly a few years ago. 

The purpose here is to advance the cause of all winds, all courses, all seas kitesailing, not downwind only with a single line kite, not as a sea kayak propulsion aid when you're too puffed to paddle, not even as a get-you-home rescue package when your yachts mast falls off.  Nor is this about the use of kites for sailing speed record attempts, a narrow field which has already had too much time and money spent on it for negligible returns by way of practical kitesailing.

To work in a practical everyday way, kitesailing requires kites and boats that are built for the purpose of doing just that, probably even sailers that are built for the purpose too.  Following is a discussion of what such kites and boats look like now and how they may develop in the future.  Discussion of GM (genetically modified) sailers for kitesailing can wait for future, less PC times.

WHERE ARE WE NOW?

Reviewing the state of the KITE SAILING  art, firstly the technical aspects:-

There are a few underlying problems that hold back kitesailing and almost all of these stem from the characteristics of kites.  Some of these are truly fundamental and may never be totally overcome but there are less of these and they are less daunting than I thought they were when the light first blinded me in 1987. Solutions or at least palliatives have come from unexpected directions which, oxymoronically was to be expected I guess.

PROBLEMS WITH KITES.

AERODYNAMIC INEFFICIENCY.

A major problem is the poor lift/drag ratio (L/D) of kites.  Put simply, kites are not as efficient as sails, their L/D rarely exceeds 4.0 while any good sail manages 10 and sailplanes get >50. 

Downwind in strong winds, poor L/D doesn't cost much performance.  A way of taking the world sailing speed record, currently held by a planing trimaran at 85.5km/hr, would be downwind in a bathtub with a parachute, 200km/hr of wind and more balls than most. 

But poor L/D does reduce downwind speed in light winds.  In true winds up to around 30km/hr, high performance sailboats tack downwind with VMG (velocity made good) faster than the true wind, and they do so by sailing UPWIND with reference to their apparent wind and in this mode L/D is all important. 

Kite traction loses out to comparable sail powered activities, and loses out badly:

*Kite buggies lose more than 10 degrees to land yachts (and about 50km/hr).  

*Kiteskaters/skiers VMG to windward is so much slower than even the most basic ice yacht that they go and play on different lakes. 

*Kitesurfers often have trouble getting back to their starting points let alone climbing to windward whereas windsurfers have nearly the best windward performance of anything that's water born and wind powered. 

*The best kiteboats don't get near similar size multi-hull yachts upwind and barely yet match them on reaches, so we try to sail only in company with over-weight (and overpriced) keelboats, preferably badly sailed ones.

Bad kite L/D is the main reason for all this but, for kiteboats, (and kitesurfing), it gets even worse:

The best angle upwind that wind powered craft can maintain relative to the apparent wind direction is calculated by what is called the COURSE EQUATION which shows this angle to be the sum of the aerodynamic drag angle (in our case arc-cotan of the kite's L/D) and the drag angle of whatever is resisting the kites pull.  For a buggy this last term is arc-cotan of the ratio of the side pull being resisted to total rolling resistance.  Typically (upwind) there will be about 1kgm in total rolling resistance for each 4kgms of side force resisted (buggy on hard sand) so the drag angle will be arc-cotan of 4/1 which is 14 degrees..  As the L/D of an averagely good traction kite is around 3.5 which is 16 degrees of "lost" angle (arc-cotan of 3.5), for a combination of this kite and the buggy above, the best possible upwind course will be 30 degrees off straight into the wind (16 +14).  This is not as good as it seems.  With this performance, after apparent wind effects are added in, a buggy on an upwind-downwind course will spend about three times as long going up as coming down, an upwind/downwind ratio of 3.

Skis on ice are very efficient and for kite skiing the drag angle is less than for buggies so they are able to go a little closer to the wind.  Their upwind/downwind ratio will also therefore be a bit better. Boats however are worse.  Basically there is a higher drag price to pay for each kilogram of side force resisted when things are being supported by water  The drag angle for such things is called the hydrodynamic drag angle (HDA) and is arc-cotan of the ratio of the side load being resisted to total drag forces.  Upwind, kiteboats lose at least 10 degrees more than buggies in similar conditions so their upwind HDA must be more than 20 degrees, implying that for each kilogram of side force resisted there is a drag price of just under 0.5kgms to pay, ouch!  Kiteboats spend up to a frustrating EIGHT TIMES as long going up as coming down.

This is not because kiteboats are hydrodynamically inferior to other boats, they're not, but the combination of hydrodynamic inefficiency and the kites inefficiency causes kiteboats to lose a large part of their potential windward performance. Kiteboats have few inherent advantages over conventional yachts (some uplift from

the kite and less heeling are about the only obvious ones) and some disadvantages (like generally they must do all turns downwind) so their deficit in performance is exposed as directly caused by the kite and improving kite L/D is the only way by which they will be able to hold their own in the wider world of yachting.

Pedants (no, not you pederasts, silly) may take nitpicking issue with some of the simplifying assumptions in the above but the principles and conclusion remains true. 

Of course we should be talking in Newtons not Kgms but we all have everyday experience of the force exerted by one kgm of mass in one gravity so this has, defacto, and rightly, become the popular unit of force outside the narrow world of engineers and scientists.

In the real world of buggying and kitesailing it may seem like we don't even attain the above angles but this is because our perceptions are effected by changing frames of reference; relative to the apparent wind, we do. 

When at useful speed, relative to the true wind direction we may only be able to hold a 50 degrees course but this is a relationship that similarly effects all fast sailing craft.  In fact ice yachts, the fastest and most efficient of all sailing craft (and holders of the outright world speed record for a while), are often knocked back to 60 degrees from the true wind by apparent wind effects, leading some traditional yachties (who tend to think of windward performance in terms of angle rather than VMG because their boats are all uniformly slow) to believe that ice yachts have poor windward performance when in fact it is the best there is.

For those pedants again, most HDA's quoted in technical literature are far better than the above but these are measured in ideal conditions, often flat water, whereas we are concerned about the real world of kitesailing when wave impacts take away up to half of every upwind metre gained (waves tend to occur when there is wind!).

THE OVERFLYING PROBLEM.

So why can't we just make kites that have higher L/D?  The required airfoil forms for L/D of 20 + have been well known at least since the 1890's.

Unfortunately, profiles aren't the problem.  The first law of kite sailing is that the kite must stay up.  Kites of L/D > 4.0 get progressively less reliable.  The main reason for this is the tendency of high efficiency kites to overfly and luff. 

A way of describing this tendency is to simplify our model of kite flying to a flier standing unmoving in one place flying a kite only in the vertical plane from on the ground directly downwind to straight up overhead.  In steady state, the kite, if its L/D is 4.0, will hold an angle of 76 degrees- but nothing in the real world of kite traction is steady state.  Our model kite launching from ground level will not, obligingly, stop at 76 degrees.  It will fly past 76 degrees, perhaps even past 90 degrees before falling back and climbing a few times with decreasing amplitude to eventually settle at 76.  If the kite flies substantially past 90 degrees, the first time, before losing forward momentum, as it drifts back downwind its lines will be slack and it becomes a falling object rather than a kite.  Recovery from this situation is unreliable and sometimes painful. 

The limit on max. L/D imposed by overflying is effected also by other factors such as the kites weight, length of lines, inherent luff resistance (delta's have special resistance to luffing), deflation resistance (for foils), by the vigilance of the flier (especially for 4 line flying when brakes can be applied to stop overflying) and by turbulence.  For all that these factors imply that the limit on max. L/D caused by overflying will be "soft", it has proven to be remarkably similar for all kite types with their best upwind VMG's falling within a narrow band.  Recently I resurrected a stack of Excalibur (2 line delta style traction kites) from 1989 and tested them again on our standard windward kite boat course.  Depressingly, tacking angles have not improved in 11 years which implies that the L/D of kites has not improved in that time either. 

RECENT ADVANCES IN KITES.

A noticeable beneficial trend however has been more power, size for size, (that is, higher lift coefficients).  The rationales for this are clear if not always understood even by designers.

Small kites have control advantages over larger kites of the same pull because they can be turned faster.  Further, the facility for controlled powering-up which rapid turning provides can, especially in lighter winds, enable small kites to outperform larger AND more powerful kites. 

But, the big theoretical advantage of small powerful kites is that they tend to weigh less than larger kites of equal power.  Less weight is a huge advantage in lulls but more importantly, the less lift that is required to support it's own weight, the more is left for doing useful work and the higher the kites useable L/D will be.

Unfortunately, there is a down-side to this trend that is a consequence of the higher angles of attack that are the means by which higher lift coefficients have been attained.  For example, foil development over the last 10 years has been towards cleaner leading edges and smoother forms (more ribs) but as this improved flow can't be used to get higher L/D without causing overflying, it has instead been applied to increasing the angle of attack to gain the higher lift coefficient that comes with this. 

The downside is that if we ever do find ways to improve the useable L/D of traction kites, a price we will have to pay, in a reversal of current trends is that  kites will become less powerful, size for size.

Back on the positive side, controllability, reliability and the smoothness of power delivery have improved out of sight.  In 1989, kitesailing was about being overpowered or underpowered with vanishingly brief bits of "just right".  Back then the average time between crashes was less than 15 minutes, now it is many hours. 

THE PULL VARIABILITY PROBLEM.

But even after these gains, uneven pull is still the other major reason for the poor upwind performance in kite traction.  Yacht and windsurfer designers have contrived often automatic ways to modify sail camber and progressively twist off their sail tips as apparent wind speed varies.  A 1999 windsurfer sail supplies almost constant force even when the wind speed varies by a factor of 4.  With this same variation in apparent wind, the best that any current kite could manage would be to limit the change of pull to around 10 times!  The practical consequence of this is that kite sailors must underpower themselves on the average so that they can survive gusts.  Putting some numbers to this; if gusts are twice the average and lulls are half (not unusual for turbulent wind) and a kiteboat has the ability to momentarily survive overpowers of double the optimum pull then on average there will be only half the optimal pull available to generate forward speed. 

Unlike the problem of poor L/D , kite underpower/overpower should gradually yield to clever design as it has for sails.  Not until the late 1980's did sail designers refine the depowering systems that are taken for granted today- and the basic form of modern sails had been common for more than 100 years.  Designing traction kites for automatic depowering without compromising L/D and reliability is horribly difficult but there doesn't seem to be any fundamental impossibility.  Traction kites have had barely 12 years of intensive development so we can hope for at least incremental reductions in the max/min pull ratio year by year.

KITESAILING UNDERPOWER/OVERPOWER.

Unfortunately, of all kite traction activities, kitesailing is the most adversely effected by variations in kite pull (overpower/underpower).

The hydrodynamic drag of kite boats (indeed of anything supported by water) is proportionally much greater than the rolling resistance of buggies or the drag of skis running on ice or hard snow. For kite boats, the loss of speed that results from periods of underpower is therefore relatively more significant.  When kitesailing, unlike for buggying and kiteskiing, using a smaller than optimal kite is not a satisfactory palliative for underpower/overpower.

Also, buggies on hard sand and kiteskiers on snow and ice attain very high speeds relative to the true wind, often 3 times or more.

Typically, for a kiteskier or buggier at 75km/hr in 25km/hr of true wind, a sudden doubling of true wind to 50km/hr will increase the apparent wind at the kite (and the flier) by only 14%.  This will be felt as an increase in pull of just 30%.  A kite boat that can only manage 25km/hr in the same 25km/hr of true wind experiences a 60% increase in apparent wind when the actual wind speed doubles momentarily, resulting in a 156% increase in pull- that is the pull will be more than 2.5 times what it was before the gust. 

Kitesurfing speeds relative to the true wind generally lie somewhere between buggying or kiteskiing (on hard snow or ice) and kitesailing so kitesurfers don't experience overpowers as high as for kitesailing, more like times 2 for each doubling of the true wind speed.  Also, kitesurfers have unique ability to withstand overpowers by jumping, in fact doing so is often the main purpose of kitesurfing.

On smaller (one person) kiteboats, overpowers usually just haul the flier out which is not much of a problem because it is often possible to park up until the boat drifts past and climb back on or in the worst case, dunk the kite and ditto.

On larger kiteboats, the kite is attached to the boat so getting hauled into the air is definitely not a good idea because the boat is going to come with you and has a distressing tendency to come down again hard, fast, and upside down.  Once or two such experiences, if survived, are a sort of right of passage and provide good pit racing conversation, more is pushing luck too far.

Large offshore capable, kiteboats experience overpowers to the same extent as small kiteboats do but have less ability to survive them. 

What can be done?  There are some answers:

·      Make longer boats: Because of hydrodynamic considerations , including the Froudes law effect that relates speed in displacement (always the mode when underpowered) to the square root of the water line length, long narrow hulls will be inherently faster when underpowered than short hulls and hence allow the use of a smaller kite to minimise overpowers.

·      Fit safety releases by which the flier can terminally depower or even release the kite in cases of extreme overpower.  The difficulty with this is that, in the stress of the moment and always hopeful the gust will taper off, fliers often don't release until it is no longer safe to- like boat and crew are 10 metres in the air with only the kite preventing their turning over and falling like a rock.

·      Take the option of flying the kite down close to the water during overpower so that the vertical component of pull is insufficient to lift the boat.  There is almost no practical limit to the side load a large kiteboat can take without capsizing- but one consequence is frightening speed, another is loads that break things- so this is definitely not an approach for the timid.

·      Use a 3 or 4 line kite.  Because a major cause of overpower is kite speed, being able to limit the kite's max. speed by braking, especially during jibes, will directly and dramatically reduce the max./min. pull ratio and yield higher speeds on all courses by making it possible to use a much larger kite.  This effect reduces with increasing true wind speed, as described below.

·      Sail only in strong winds:  Kite generated apparent wind effects, (after gusts, the major cause of overpowers) reduce as the wind speed increases.

This last is an interesting relationship and requires detailed explanation.

If the average wind speed is just 10km/hr, an averagely efficient kite will attain 40km/hr so the nominal ratio of its pull when "parked" overhead or at the edge to that when at top speed, will be 16/1.  In practice, at this wind speed, boat speed will also be about 10km/hr, which will increase the minimum apparent wind that the kite will experience to 14km/hr and drop the max./min. pull ratio down to around 8/1.  Reaching performance in steady winds of 10km/hr will therefore be satisfactory but upwind or downwind courses, if possible at all, will be very slow (compared to conventional yachts) and any major change in the kite's position relative to the boat could generate brief but frightening overpower.

In steady wind of 60km/hr, the maximum kite speed will not be 4 times windspeed as it was in the 10km/hr wind but only about 1.5 times, say, 100km/hr, so the nominal max./min. pull ratio will be 2.8/1.  The contribution that boat speed (say 25km/hr reaching and downwind, 12km/hr at best VMG upwind) will make to apparent wind at the kite will be around 5km/hr which drops the ratio to 2.4.  At 2.4, controlled, all course kitesailing is possible.  Reaching and running (downwind) speeds will be close to similar size multihull sailboat performance and upwind VMG will be about half ditto (limited more by kite L/D. than max./min. pull effects).

LIGHTWIND KITESAILING.

Light wind will always be a limitation for kitesailing because if there is not enough wind to keep a kite in the air (currently the best light wind kites require around 5km/hr of wind) then kitesailing is by definition impossible.  By comparison, yachts can continue to move right down to 2km/hr or so of true wind, albeit very slowly.  In fact, when competently sailed, yachts can retain reaching, running and even limited upwind capability in winds as light as this.

As alluded to earlier, when wind speed decreases, the possible courses available for kite sailing narrow.  Older style traction kites that require a minimum of 10km/hr or more, can be kept up in the light only by "figure eight" flying.  This precludes upwind courses because the angle loss from this figure eighting costs more than all the available windward performance.  Only broad reaching and downwind remain possible and then only if the downwind component of the boat's velocity doesn't take too much off the available wind speed.  Although long lines help, going downwind at any more than about 5km/hr in 10km/hr of true wind with a kite that needs all of that to stay up generally risks over running the kite and if the wind drops below say 8km/hr (see below) kitesailing on any course ceases to be possible.

For latest generation kites and specialist light wind kites that require only 5km/hr of true wind it is not necessary or desirable to figure eight and all courses remain possible at that windspeed.  As the wind drops further, available courses narrow until only one direction is possible, usually a broad reach at about 120 degrees from the true wind.

Light wind kitesailing techniques are beginning to mimic best practice for ditto yachting, the underlying principle of which is that maintaining boat speed takes priority over direction and all movements are minimised.  There is so little spare energy available from whisper winds that all unnecessary movement (even rocking) of the boat or kite costs boat speed and the boat speeds contribution to the kite's apparent wind is crucial to keeping it up.  Instead of figure eighting, kites are "suspended" at the edge by applying quite extreme 2 line control to cause a large fraction of the kites total area to present in the horizontal plane even while the spanwise axis of the kite is approximately vertical.  For this technique to work kites seem to have to weigh less than 100gms per square meter and be efficient as well.  This has only recently become possible. 
That it is possible to kitesail in winds lighter than the minimum the kite needs is surprising to the uninitiated but depends on using either a minor gust or momentarily higher apparent wind from moving the kite to get under way, then never letting the kite get caught at the edge with no way out nor letting boat speed drop to zero.  This requires a high level of concentration, and more skill than any other aspect of kitesailing, especially when jibing, and is a technique much more easily learnt first by buggying in light wind on a hard surface. 

The extra margin of light wind performance to be gained is welcome for all that.

Further gains in light wind capabilities?

It is now possible to kitesail in winds so light that boat speed is too slow and too boring for all but the totally obsessive like myself, so improvements aren't essential.  However, because light wind capability also defines our ability to withstand the not infrequent lulls that occur even when the average wind speed is quite strong enough for exciting sailing, improvements will still be worth having.

In the limit, lighter than air gases may have a role but I doubt this because:

·      Containment of hydrogen and helium (very small molecules) requires much heavier fabric than now required for kites so will offset some of the gains to be made.

·      Leakage can never be entirely eliminated and refilling is expensive as well as awkward (high pressure gas cylinders would have to be carried).

·      Permanently inflated kites are a safety problem in stronger winds when they won't stay down.

·      Light weight pressurised envelopes are easily punctured and not really suitable for the robust demands of real world kite sailing.

·      Heavier than air kites already enable kitesailing at wind speeds lower than anyone is likely to want to kitesail in.

In their favour, lighter than air kites offer about the only hope there is for relaunching from the water in very light winds and could maintain flying thru lulls that may not be possible with any other system.

WATER LAUNCHING SYSTEMS.

For viable kitesailing it is necessary to be able to launch kites, change kites and to relaunch kites that land on the water.

Of the three main kite related problems that effect water based kite traction, this is the most obvious and therefore the one that gets the most attention. 

There are many possible solutions and all of them have potential for kitesailing.  The options that are shared with kitesurfing are;

*CLOSED FOILS: 2 and 4 line parafoil style kites that have various arrangements of non-return valve type inflation allowing some chance of relaunching from water.. In their current forms, after touching the water, such kites offer only a brief period when relaunching can be successful.  They also require more than say 15km/hr of apparent wind (in this case, the difference between the actual wind speed and the boat's drift speed) to successfully relaunch.   Because they can also be relaunched from nose down, 4 line closed foils are more reliable than 2 line versions.  Closed foils are likely to improve in all respects with more development.

*WIPIKA/NAISH 2 or 4 line pumped up structure sled style kites:  These are currently the best water relaunching kites available.  Relaunching is almost totally reliable when the apparent wind is more than 20km/hr.  While kitesailing, on the rare occasion when their skins invert, even in the absence of any wind-in systems it is possible to retrieve the kite, rearrange it and let it drift out again for relaunching.  There is a more extensive analysis of the WipiKa design in the "Kites for Kite Sailing" section that follows.

*KITESKI, Corey Roeseler's and other wind-in/brake-out bars:  The principle here is that after crashing, the kite is winched back to the flier, relaunched then let out again.  One not obvious requirement of this is short bridles as it is devilishly difficult to relaunch a kite over water if the bridles are longer than your arms- this fairly much limits the system to rigid frame kites (except on kiteboats that can have launching cranes or gantries as described later).  Relaunching in light winds is also difficult as anyone who has tried to launch a wet delta in almost no wind will attest.  I have built useable 4 line wind-in/brake out systems that are satisfactory for use on kite boats while currently being too complex for kitesurfing.

*C QUADS (the versions with built in flotation). Being single skin and 4 line is an advantage but C Quads generally have less relaunchability from water than 4 line closed foils because they have almost no drift back ability.  When the flier is not drifting, relaunching is quite reliable but is a learned technique.  When the wind is more than, say, 30 km/hr there is some chance of relaunching, even by a floating flier, but only if the lines are tight.  There are many possibilities for improving C Quad water launching but those tried so far have compromised performance.

*3-D LAUNCHING FRAMES.  To my knowledge this has never been tried but would certainly be possible.  The principle is to construct a three dimensional frame around the kite with floats at all corners so that no matter which way the kite sits on the water it can be re-launched.  The extra weight and drag of the frame and floats would be disadvantageous as would the safety issue of being unable to get the kite to stay down when required in strong winds.  

*METAMORPHS.  Back in 1990 I wrote an analysis of kitesailing which included a list of possible water launching systems.  Re-reading it now is a bit embarrassing, not that it is so far off the mark, just pompous sounding.  I hope this was the immature self-righteousness of a recent convert rather than a personal characteristic that can only be recognised in hindsight!   But, listed, was a launching possibility that has been forgotten.  This is to rig a traction kite so that it can be flown as a single line kite, launch it in this form, and then have a timer or other means (a pull cord or?) that converts the kite back to its "adult" form.  The advantages of this are that the self stability and generally much more forward bridling of single line kites make them much easier to launch off the bridles and in light winds.  Their lesser pull for the same size would also be an advantage, especially while letting out.  For relaunching a typical 4 line traction kite, I can envisage the possibility of winding the lines back onto the handles, setting the kite for single line flying, launching, letting the lines out again by hand then re-setting the kite to its 4 line form.  Bridle and line snarls, as always, will be the biggest challenge.

*LIGHTER THAN AIR kites as described in an earlier section;  I'm not aware that any practical traction kites of this type have yet been built but maybe they are possible.

*PILOT KITES  Using a single line pilot kite to lift the main kite.  Tests have shown that a pilot kite just big enough to get the main kite started typically reduces the overall kite L/D by about 15% if left up.  For some courses this is acceptable, particularly because it improves the reliability of the main kite.  When leaving the pilot up is not acceptable, it could be a timer released biodegradable throwaway or it would be possible to rig a system that allows this pilot kite to be retrieved while leaving the main kite flying.  Launching small single line kites from a boat is easy, and is possible even for kitesurfers.

There are also water launching options that are suitable for kitesailing boats but not for minimalist activities like kitesurfing, kite water skiing and body dragging: 

*BALLOON LIFTING  As for the pilot kite system above but using a lighter than air device as the lifter.

*GANTRIES and crane relaunching systems.  A pole or poles rather like those used for game fishing trolling lines, when combined with 2 or 4 line winch systems, enables relaunching of almost any kite.  A nasty trick that kites do while being relaunched from a gantry is to persistently hang upside down twisting around in the wind rather than sit up and fly.  If there are 2 or more people on board the easy remedy is for one to locate the kites leading edge using a hook on a pole as launching initiates.  Otherwise it is necessary to rig extra line(s) to the kite or fit bars and clips to locate the kite's leading edge at the gantry.

*BALLISTIC LAUNCHING.  This concept requires a kite to be packed small enough to be fired out of some type of cannon and arranged so that it unfolds or inflates at 15 or more metres up as the lines tighten.  Energy could come from explosives, bungies, compressed air/gas or a fuel air combustion.  Sound like fun to do, could work.

*MOTOR LAUNCHING.  In this system (which has been successfully trialed), the kite is placed in the water and the boat motors back upwind until the lines are tight and then keeps pulling until the kite launches.  Easiest when there are 2 or more people on board so that one, with a boat hook, can keep bridles clear of rudders etc. for the first few metres, it does require a motor- but any useable offshore kite boat has to have one anyway for safety, for docking (although I have successfully docked an 8m keeler solely by kite power), and when there is no wind. 

The last of these is the one I favour.  Not often thought of as a relaunching option, it is the most reliable, works in all winds from zero up and doesn't require compromises in kite design that limit performance and efficiency.  Ocean capable kiteboats require not only the facility to relaunch downed kites but must be able to replace damaged kites and swap kites as wind conditions change.  Motor launching allows all of this. 

The issue of "purity", of being ineligible to enter I.Y.RU. (International Yacht Racing Union) events because of motor use is a non-issue as far as I can see.  Not only would exemptions almost certainly be available if kitesailors choose to join the yachting establishment- they are for other specialist sailing classes- but nobody who has witnessed the elegance power and terror of kitesailing can then fairly question its fundamental status as one of the most elemental of wind powered activities.

KITES FOR KITESAILING.

Every type of traction kite can be used for kitesailing and I suspect that no one style will establish itself as best for all conditions in the foreseeable future- another reason I favour the motor relaunching option- it allows relaunching of all types.

Following is a brief analysis of some of the various types of kites that are (or may be) suitable for kite traction with their advantages and disadvantages for kitesailing.  One of these types, as far as I know, hasn't been tried for kite traction and it may be the best of all; theoretically it has many advantages- and a niggling little safety worry!

*DELTA style 2 line framed kite.  These currently have the best automatic depowering characteristics of all traction kites (by twisting off at the tips in the same way that windsurfer sails depower by twisting off.), very good lift coeff's (power for size), excellent L/D (good upwind) and unique luff resistance. 

On the down side, above about 5 sq.m's, even with carbon it becomes difficult to make frames for deltas that are strong enough within weight limits for good light wind flying.  Additionally, rigid frame kites like deltas tend to break up when swilled around in breaking waves and the bigger they are the worse this tendency is. 

These factors probably preclude a role for deltas on larger kiteboats.  For smaller, up to 4m, boats and for boats up to 7m or so in stronger winds when structural weight is not so important, they work very well. 

Except perhaps in very strong winds, to mitigate periodic overpowering, larger kite boats require kites with controllable brakes.  Therefore, unless 3 or 4 line deltas can be developed, their role in the future of kitesailing will be limited by this also.  There have been some 4 line deltas but none has yet established a niche in traction kiting for reasons that may not be fundamental.

*PARAFOILS (usually now shortened to just Foils).  Well developed in 2 and 4 line versions, up until very recently, most observers considered foils and the future of kite traction to be synonymous.  They may still come to dominate but will now have to improve rapidly to meet the challenge from single skin flexible framed kites (WipiKa/Naish and C Quads). 

For large kiteboats, foils hold a very big advantage in their ability to be scaled up with almost no weight per unit area penalty, at least to 30sq.m's or so.

Foils can be made with closed leading edges so that internal pressure and shape are retained for some time after the kite lands on the water, providing a window of opportunity for relaunching.  For current versions that I have used, including the Peel variant with this feature we marketed briefly in 1993, this time span is only 30secs at most, but why can't it be minutes?, it's just a function of valve sealing and fabric impermeability.  I have no doubt that closed foils are just at the beginning of their development, that they WILL mount a serious challenge to other traction kites, for kite surfing especially, and not least because their form retention has had an unexpected beneficial spin-off in improving their ability to recover from overflying.

Their "drift back" capability is also the best.  This is the ability, when on the water, to drift downwind faster than a kitesurfer floating in the water or perhaps even faster than a drifting boat, thereby keeping their lines tight to facilitate relaunching.

Another advantage of foils, shared with NASA style kites is their ease of packing.

The downside of closed foils is a tendency to burst when impacted onto water.  All foils are subject to this but closed foils are worst and the larger they are the more likely they are to split.  Foils smaller than 4 sq.m's are fairly robust but this is nowhere near big enough for even moderate size kite boats.  The critical dimension is not total area but cell size, therefore closer spacing of ribs reduces the problem- and this makes for smoother form which improves performance so is a good idea anyway- but adds to weight so has a cost.  Stronger fabric (also heavier) , helps and it may be possible to develop some pressure release system that limits pressure build-up.  Another answer is to not crash the kite, and it is true that experienced users now very rarely lose control totally (like only once every 20 or more hours of flying) so the bursting problem is not insurmountable.

Lastly, current closed foils initially inflate very slowly which is frustrating, but fliers can adapt to this if other advantages are worth the wait and there are possible technical solutions also.

*WIPIKA/NAISH.  Sled style traction kites that can be flown with 2 or 4 lines (and some users rig them for 3 lines), Bruno and Dominique Legaignoux's breakthrough of the early 90's has revolutionised water based kite traction activities by providing reliable water relaunching without the need for wind-in/brake-out bars.  The WipiKa kite structure comprises an inflated leading edge tube (fabric outer with inner bladder) and ditto curved battens which simultaneously create form and provide sufficient flotation for excellent "drift back" capability.  Their semi-circular leading edge shape and more than adequate buoyancy allows relaunching from all positions including nose down even for 2 line versions.

To gauge their usefulness for large kiteboats it is necessary to consider what changes are required in the structure of the WipiKa kite as its size is increased.  Dimensional analysis reveals that buckling forces and structural resistive forces are each proportional to a linear dimension cubed.  Hence, provided that the inflation pressure remains constant and the diameters of the leading edge and batten tubes are scaled linearly it will be possible to scale WipiKa's without weight per area penalty until fabric limits are reached at 30sq. metres or more as for foil kites.- with just one exception.  The wall thickness of the inflated tubes will also have to increase in direct proportion to the kites linear dimension if their hoop stress is to remain constant.  In mitigation, it will certainly be possible to make the tube outers from higher strength material like Spectra.  Wipika/Naish kites should therefore be scalable to the sizes required for larger kite boats.

However, there are some downsides of the current WipiKa/Naish kites that make them less than ideal for kiteboats, and especially for large kiteboats.

-Their lift coefficients are about half that for good foil, C Quad or delta traction kites; ie for the same pull they have to be twice the size.

-Currently their effective L/D is not as high as for other traction kites.  By upwind angle they are usually about 10degrees down although in winds greater than around 50km/hr this deficit largely disappears

-Their inflated tubes are heavy compared to the structural elements that perform the same function on other traction kites so, although they scale up without much weight penalty, their starting point is heavier and this will limit their ultimate size.

-They turn very slowly and bigger versions are the slowest.  Sluggish steering is an advantage in strong winds, but a big disadvantage in light conditions when quick turning can be used to momentarily boost pull.

-Motor relaunching, which is available on larger kiteboats, makes inherent water relaunching characteristics largely irrelevant so any performance compromises that water launching features have required are a price that doesn't have to be paid.

-As their size increases, at some point the stored energy in their pressurised tubes may become a safety/regulatory issue- but we can just keep them away from people.

I am hopeful that most or all of these disadvantages are not inherent and will yield to incremental improvements.  Already it is clear that the Naish versions have better upwind performance for kitesurfing at least, so improvement is possible.

*C QUADS  Single skin 4 line traction kites with flexible (usually carbon rod) structures..  Their inherent simplicity makes them inexpensive to manufacture and they combine high lift coefficients with an L/D that is ahead of most other traction kites.  In just one year since their release these kites have taken a substantial share of the world traction kite market.

For kitesailing they have advantages and disadvantages;

-They have good depower, both automatic and by brake control, albeit embryonic when compared to windsurfer sails, but superior to most other traction kites.

-Their excellent L/D (and auto depower) have lifted the windward performance of kiteboats to a level that can sometimes match conventional yachts. Instead of having to hide our disabilities away in private, now we can go out to play with the other kids, on crutches still, but upright and smiling.

-Their light wind performance (largely the consequence of being light weight kites with high efficiency) has made all course kitesailing practical in conditions when even downwind sailing was not previously possible.

-Their flexible structure generally doesn't get damaged while in waves (but can in breaking surf).

-Being single skin they don't hold water.

-They are ideally suited for motor relaunching.

However;

-Their structural weight starts to limit light wind performance (that is, causes the kites weight to exceed 100gms/sq.m. ) at somewhere around 20 sq.m's and by 30sq/m C Quads will probably not perform better than foils in light wind.

-In larger sizes, coil packing becomes impractical and it is necessary to de-sleeve and fold as for deltas and other cumbersome framed kites.

-Their various performance advantages over other traction kites tend to diminish as wind speed increases above around 40km/hr.

-Their multiple long bridles are a menace around rudders, propellers and shellfish- but not as bad as foil bridles.

Of course, C Quads are not yet fully developed so some or most of the disadvantages listed above may be overcome during the next few years.  There is reason to believe that the loss of their performance advantage in strong winds is a characteristic of the first generation design rather than inherent.

*NASA WINGS and similar style single skin stickless kites, 4 and 2 line.  Although usually disregarded as "serious" kite sailing kites because of their poor L/D, single skin soft kites have many of the characteristics that are required for larger kite boats:

-They scale to larger sizes than all other styles of traction kite before weight/unit area needs to increase.

-Packing is the best there is, best there can be.

-They are very well suited to motor relaunching.

-Their light wind performance is up with the best.  

Against these positive features, only their L/D, which is about 15degrees behind that of other traction kites, prevents their being the ideal kiteboat kite.

Is it possible to improve their L/D without other compromises?: 

High drag is fundamental to the design in that it derives from the extreme angle of attack that is required to hold the shape without using any structure.  Even with this high angle of attack, the leading edges are wrinkly, a further source of drag that costs L/D. 

The minimum necessary improvement of, say, 10% upwind may be possible, my guess is there's a 50/50 chance of this happening in the next year or so.  If it does, single skin stickless kites will own a big bit of the future- that is, unless other designs improve apace. 

*FLEXIFOILS  Back in 1982, Ian Day and crew on a set of extended Tornado catamaran hulls established a 28sq.m. class sailing speed record by averaging 45km/hr over 500metres while using a stack of Flexifoils.

This is a speed I have not yet often exceeded while kitesailing.

They were also able to tack; that is turn upwind, a feat that I have only recently duplicated.

They also left the water on occasions; one time to the extent of 15m at the apex of a 60m trajectory; a feat that I have absolutely no wish to duplicate having been scared thoroughly shitless by smaller jumps a couple of times in the late 80's- once ending up, boat and all, in a car park.

How is it, if they were so successful then, that Flexifoils are so rarely used for kitesailing now?

The answer is that in fact kitesailing has advanced a lot since those days and that, knowing what we know now, the 1982 performance would be relatively easy to exceed if this was the goal.

The goals of the last 10 years have instead been to make kitesailing practical and easy, to extend the wind range (especially towards the low wind end), to contrive reliable water relaunching systems and to design marketable boats.

Flexifoils, as kites have excellent L/D- still as good as anything there is including C Quads- but their power derives from speed (faster than all other traction kites), not from lift coefficient (about half that of contemporary kites).  Because the pull from a kite is proportional to the square of its velocity, fast kites generate lots of pull when moving across the sky but very little when hovering at the edge or overhead.  These are exactly the characteristics that aren't desirable for kitesailing as they make for underpower on the average punctuated by short bits of wild overpower - hence the jumps. 

On the plus side, although boat speed will build up slowly (as it does buggying with Flexifoils) it will eventually be satisfyingly high.

These extreme apparent wind effects will also proportionally decrease with increasing wind speed, the reasons for which were explained earlier, so, Flexifoils are relatively more useable in stronger winds.

Also on the negative side:

-Their use of a leading edge spar supported only at its ends to take all the loads make them difficult to scale up to larger sizes within weight limits for good light wind flying.

-In larger sizes they turn very slowly which is much more of a problem for a kite style that derives its power from speed than for slower flying higher lift coefficient kites.

-Stacking multiple smaller Flexifoils is the usual palliative for both of these problems but when they swirl in the surf, stacks get more tangled up than all the worlds kittens and all the balls of wool could manage in all eternity- I exaggerate a bit but you will get the idea.

-Flexifoils, because they're "not flying 'till they're flying" are a more difficult proposition for reliable water launching than any other style of kite- even with motoring.

For all that, I remain in awe of Ian Day and the results he achieved.

*ROTATING WING kites.  An untried idea that has potential. 

The reason that helicopters are so relatively unaffected by turbulence, making them ideal for mountain rescue activities, is that the average speed through the air of their blades is 400km/hr or more, so the percentage change in gusts is small. 

This relative immunity to gusts also works in exactly the same way for rotating wing kites.

When a gust takes the wind speed from 30km/hr to 60km/hr, conventional traction kites experience a 300% increase in pull. 

In the same wind change, for a 2m diameter rotating wing traction kite running at 600rpm, there would be only 9% increase in lift. Apparent wind effects are similarly softened for rotating wing kites and I would expect such kites to have almost the same pull when hovering at the edge of the wind as when at maximum speed on their way from one side to the other.  Of course if the kite spends any significant time in higher apparent wind then the rotor speed will increase proportionally, but in practice, the rotational inertia of the spinning blades will prevent any substantial increases in rotational speed in the time it will take to shift the kite from one side to the other unless very long lines are used.

Although the wing (blade) component of rotors are very efficient in themselves (L/D> 20), overall, rotating wings lose a lot of this potential by interference and etc. but could certainly match that of existing kites. 

Whether rotating wing kites are subject to the same overflying imposed L/D limit as other traction kites remains to be seen.  Superficially it would seem that may not be.

Such a kite could take different forms; either vertical axis(disc type) or horizontal axis (cage or rotor type).  Although most single line rotating wing kites are of the horizontal axis rotor type (and I have seen "toy" type 2 line versions of these) it is unlikely that such kites could attain the necessary L/D for serious kite traction use- although the 1920's Flettner rotor ship sails, using external power for rotation (diesel motors), did reportedly get L/D's above 5 (after discounting for the supplied power).

Considering only the vertical axis "helicopter" style, then:-

-Such vertical axis disc type traction kites would almost certainly use moulded carbon fibre blades, maybe foam cored, rotating on a central spindle the lower end of which would be "cranked" to set the bridle point.

-For control and to neutralise gyroscopic effects there would probably be a counter rotating pair of rotors disposed side by side.

-Interestingly, a rotating wing kites generate similar lift to that of a conventional traction kite with area the same as the disc area swept by its rotating blades.  A consequence of this is that such a kite although constructed of solid materials, may not offend the 100gm/sq.m rule that defines good light wind performance for traction kites.  

-For launching, either the kite would have to be held in the windstream until rev,'s built up enough or some external power supplied to do this as is used for gyrocopters. 

-Perhaps such a kite could be launched from the water by holding it up while speed builds then letting go- easy on a boat, maybe even possible when kitesurfing.

-Intriguingly, there is the possibility of incorporating some energy storage system into such a kite.  The rotating mass of the blades will provide some anyway but this could be enhanced by adding a small high speed gear driven flywheel.

-Energy storage would further soften the effect of gusts and apparent wind changes and could enable lulls to be bridged.

And the "little" safety niggle?  Multiple 2 metre blades whirring at 500rpm or so (and unable to be caged for efficiency reasons) could be a problem, though not for kiteboats alone in the open ocean if the crew are caged instead.

*HYBRID DESIGNS. A totally original traction kite could suddenly appear at any time and from one point of view is more likely to now than at any time in history because there are so many people working to do just this, spurred by the explosion of kitesurfing.

On the other hand, maybe everything new has already been thought of; and it is true that finding major new designs is becoming increasingly difficult as the field of traction kiting gradually fills in.

In my view, more likely than either something completely new or nothing new is that new kites will be created by combining various elements of existing designs.

Considering the desirable characteristics of known kites:-

-The twist-off characteristic of deltas that give a degree of automatic reefing similar to bendy mast yacht sails.

-The delta anti-luffing that derives from nose-ward migration of the C. of P. with decreasing angle of attack.

-The water relaunchability of the WipiKa, even in 2 line form and in lightish winds.

-The ability of inflated tubes to withstand extreme deformation and pop straight back out without damage.

-The tendency of high lateral area kites to stay where they are put while attention is elsewhere in strong wind.

-The packability of foils and single skin stickless kites.

-The overflying resistance of closed foils.

-The power control of C Quads.

-The high lift coefficients of CQuads, deltas and foils.

-The high L/D of C Quads and Flexifoils.

-The light wind performance of C Quads and some foils.

-The simplicity of having just 2 lines.

-The control benefits of 3 and 4 lines.

Putting new kites together from existing elements so as to get more of these desirable characteristics in one kite will be a good starting point but whether such hybrids can beat out incrementally improving existing styles in the long term remains to be seen.

HULL AND FOIL ARRANGEMENTS FOR KITEBOATS.

There are some fairly inescapable hydrodynamic fundamentals that define what will and won't work:

*WATER LINE LENGTH determines maximum speed in displacement mode.  Generally called Froudes Law, for non-planing, non hydrofoil boats there is a relationship between maximum speed and the square root of the water line length. 

Not an absolute limit, Froudes law is usually used to define a "hull speed" beyond which each, say, 10% increase in speed will require the propulsive power to double. 

For long narrow hulls, those with length/width ratio of 15 or more, the Froude barrier becomes softer, and it is possible to push thru to the so called "forced displacement" mode, but at significant drag price.

A typical example of the use of Froude's law would be to calculate, for the same power, how much faster 7m hulls are than 4m hulls.  The answer is 32%. (disregarding skin friction which for small boats isn't usually a big factor by the speeds at which the Froudes limit is being pushed anyway).

*DISPLACEMENT HULLS.  It is difficult to list an average figure for displacement hull L/D.  It is very high, 20 or more, at very slow speeds but rises sharply as the "hull speed" is approached.  For course equation purposes the L/D that matters is the ratio of the horizontal component of the kites pull to the sum of the hull drag from supporting the boat plus crew and the fin drag from resisting the lateral component of the kites pull.   For a 4m catamaran kite boat on an upwind course at 12 km/hr with kite pull of 40kgms, the hull 'weight' drag figure is about 14kgms (hull L/D of 7, total weight 100kgms)and the foil "side force" drag is about 5kgms (foil L/D of 8, lateral load 40kgms x cos 15) for 19kgms total drag.  In this example the overall L/D is therefore 50/19 = 2.63 and the HDA, arc-cotan (L/D) = 21degrees. 

Using this boat with an average traction kite of L/D 3.5, ADA, arc-cotan (L/D), = 16 degrees, the course to windward would therefore be 21 + 16 =37 degrees which is about what we get, and so it should be because I tortured these numbers until they confessed to what I wanted them to say.

*FOILS operating close to the water surface, whether used for lifting (usually called hydrofoils) or to resist lateral forces (fins, daggerboards, rudders and centreboards), have a practical upper speed limit of about 85km/hr.  Except for high drag wedge profiles, at around this speed it becomes increasingly difficult to retain attached flow on the low pressure side and the foil cavitates.

Maybe 85km/hr sounds plenty for our purposes but this is the limit only in ideal conditions.  Foils operating in waves and especially in breaking waves suffer from cavitations near relative, ventilation, even at much lower speeds.  The proximate cause is a bubble of air, either sucked down from the surface or from aerated water, that attaches to the upper or lift side of the foil.  Ventilation simultaneously destroys the foils lift and increases drag.

A partial answer is to position the foils under some part of a hull well away from where the atmosphere can leak in, or, for surface piercing foils, to place a series of low fences along their upper surfaces just below water level. 

There is no total solution to ventilation in rough water, but it helps to choose foil forms that are resistant to ventilation even at some cost to efficiency.

*RESISTING LATERAL FORCES.  At higher speeds, under water foils are more efficient for resisting side load than hulls.  In L/D terms, each kgm of side force that is resisted by a hull operating in displacement mode will cost around 0.2 or .25kgm of drag, a bit less at low speed.  (Hulls aren't as efficient at resisting side forces as at supporting weight.)  For a foil shaped centreboard, daggerboard or fin, the drag for each kilogram of side force will be only 0.15kgm, or even less if the foil is well fenced against ventilation at its upper end. 

Using planing surfaces to resist lateral loads as well as supporting the weight of the boat and crew is a very high drag regime and will increase the overall HDA to 25 degrees or so.  For kite powered boats, this drops their upwind performance back to kitesurfing levels, as would be expected because most kitesurfers use a component of their planing lift to resist side pull, their fins being mainly for directional stability.

*PLANING HULLS are less efficient at low speeds than displacement hulls but are not subject to Froude's law so they can be driven to much higher speeds before their drag curve starts to rise steeply- and this time it is skin friction that becomes limiting.  About the only scale effect that planing hulls are subject to is that bigger hulls are less effected by bigger waves.  At usual kiteboat speeds, typical planing hull L/D is 3 to 3.5  (one kgm of drag for each 3 or 3.5 kgms of weight being supported).  For planing hulls that are relatively short and wide there is a drag "hump" to get over as planing establishes.  As hydrodynamically literate visitors to Bangkok (no, not you pederasts, silly) will have noticed, "Asian Longtail" river boats exhibit almost no transitional drag hump between displacement and planing.  If a hulls length to width ratio is above 5 or so, transition to planing is smooth but not without cost.  Once into planing mode, long narrow hulls have higher drag than the short Rolf Sturm type.

*HYDROFOILS.  Potentially hydrofoils could be more efficient than either displacement or planing hulls for the speed range that kitesailors are interested in.  Weight supported/drag ratios of 10 or more are claimed in

flat water conditions although 7 or 8 is more realistic.  Of course, as for all kite sailing except downwind there is also the drag associated with having to resist lateral forces to add in so the overall HDA for current hydrofoil kiteboats, upwind, are similar to that for multi hull kiteboats at about 20 degrees.  In choppy conditions hydrofoils lose some efficiency but not too much provided the hydrofoils hull(s) remain lifted clear and its foils don't ventilate.  In real waves, and particularly in breaking waves, hydrofoil kiteboats lose it completely although maybe not if big enough- with deeply immersed foils and average water to hull clearance of say 1metre.  Sudden ventilation at high speeds can cause a flat spin or capsize which will usually, putting it politely, "dismantle" the boat.  Russel Long did a flat spin at 75km/hr on "Longshot", a Ketterman designed sailing speed record attempt sailing hydrofoiler and I've tried out every type of crash on kite hydrofoilers, and don't want to again.

HEELING.

Yachties quickly identify the possibility of applying the kites pull to the boat at or near its roll centre as a big advantage.  On conventional sailboats the wind force on the sail or sails must necessarily act at a point substantially above deck level and gives rise to a heeling moment, offsetting which has largely occupied sailors and sail boat designers since yachts were first thought of.  Heavy pendulum action keels are one of their solutions, another is the form stability of multihulls and yet another is bodies hanging off the windward side on trapezes.

In theory there is no correct point for the kite pull to pass thru for zero heeling because the boats resistance to this pull is both inertial (acting at it's centre of gravity), and hydrodynamic (acting at the hydrodynamic centre of lateral resistance), and these points are not coincidental.

In practise it is possible to apply the kites pull so as to substantially reduce heeling effects.

Unfortunately, if by doing this the fliers connection to the kite becomes indirect (thru pulleys or etc.) there will be considerable loss of control and "feel". For smaller kiteboats especially, controlling the kite in the usual way with hands, arms, shoulders and occasionally every other bit of anatomy is by far the most reliable.  Direct flying offers optimum kite performance and allows recovery from many situations that inevitably end in kite dunkings with remote control flying systems.

The price that must be paid for this level of kite control is heeling, as the kites pull will be well above the boat's roll centre.  This makes some form stability necessary for small kite boats.  Monohulls with significant width are just satisfactory, multihulls have more than enough.  Don't even dare to suggest a weighted keel!

For larger kiteboats the heeling moment will usually be less because the kites pull will come in proportionally lower- fliers don't scale up in size with the boat, apart from their dicks that is.  (In the PC version of this please read 'ego' for 'dick').  Also, when the kite pull can be hundreds of kgms it is necessary to have it connected to the boat anyway, so, for larger boats, there is little extra disadvantage in contriving for it to be approximately in line with the boats roll centre and worthwhile reduction in heeling by doing so.

However, when using a kite that is powerful enough to provide satisfying boat speed the pull from the kite can vary erratically between almost nothing and enough to cause the entire boat and crew to lurch at least partly out of the water on occasions.  This huge variability compared to the relative docility of conventional sails, not heeling moment, is the major destabiliser for kite boats and requires the same solution, that is, adequate inherent boat stability.

Until kites become as docile as sails that is, (like probably never!)

HULL ARRANGEMENTS.

SMALL MONOHULLS.

As single person kite boats, monohulls work very well, in fact the only volume manufactured purpose built kitesailing boat there is (our one) has this form.  They are popular with buggiers who aren't up to kitesurfing  (or who sail where the wind is too light for kitesurfing).  There is a detailed description of this particular boat in a later section, but small monohulls for kitesailing generally:

-are easily transportable, requiring no assembly/disassembly.

-are manoeuvrable, the quickest turning of all kiteboats.

-can be of planing or displacement form.

-lack the heeling resistance of multihulls so don't accept overpower as well.

-are best in sheltered water, difficult to keep upright in big surf.

-go to windward easier than kitesurfers but are slower,

-but can be used in much lighter wind

-and are generally regarded as fun to sail.

LARGER MONOHULLS.

Sailing on the edge of capsizing is part of the fun of sailing small boats but for larger craft the consequences of capsizing are much more serious.  Larger (multicrew) monohull kiteboats become possible when heeling moments can be reduced to a manageable level by getting the kites pull down to deck level. To be useable they would also require sufficient size and form stability to not easily capsize in ocean sized waves.  This implies a minimum of probably 8m long and 2.5m wide as kite boats do not have stabilising lumps of lead hanging underneath like yachts do. 

For larger monohulls also, lesser inherent stability will reduce the ability to accept overpower relative to a multihull of similar length. 

This noted, a large monohull kiteboat would:

-turn tighter and easier than a multihull- important when almost all turns have to be jibes.

-have by far the best possibilities for working space, living space, and head room.

-with less pull and provided it is not too fat, be as fast as a multihull in light winds,.

-occupy less (and hence less expensive) docking space in marina's etc.

-transport more easily on the road than a multihull (that has to be dismantled or folded).

-transition from displacement to planing mode for high speed (if of suitable hull form).

-have inherently more strength than a multihull- no beams or external structure.

-be less expensive to make than multihulls of the same size.

-be more readily accepted by the yachting establishment hence more easily marketable.

PROAS.

Proa's are multihulls that are longitudinally symmetrical but laterally asymmetrical (trimarans and catamarans are laterally symmetrical but longitudinally asymmetrical).

Instead of tacking (upwind turns) or jibing(downwind turns). Proas "shunt", that is they stop and then restart in reverse.

For downwind sailing this is awkward. On a proa when changing from a course that is just a few degrees on one side of directly downwind to one just the other side it is necessary to turn upwind a bit, stop and restart in the opposite direction.

For upwind sailing the proa shunt is more economical than the time and upwind VMG wasting jibe that is the usual for other kiteboats.

On short courses the loss may be more than the gain but on the open ocean it is not significant.

Proa lateral asymmetry simplifies the layout for the flier and for kite attachment because the kite pull direction relative to the boat axis need not vary by more than 90degrees.  For laterally symmetrical boats, 180degrees is required.

Proa laterally asymmetry also allows foil and hull shapes to be better optimised for resisting lateral forces but the requirement for longitudinal symmetry cancels this advantage. 

Proa kite boats have been built and wakeboard style kitesurfing boards are in fact proas but there doesn't seem to be any great likelihood that the proa style will become dominant for kiteboats:

Firstly, at higher speeds the requirement for longitudinal symmetry costs more hydrodynamic inefficiency than is gained back by lateral assymetry.

Secondly, having to pull up into the wind to change direction during fast downwinders is a recipe for overpowering and will definitely be accompanied by air time- and we don't want to make the kitesurfers jealous.

TRIMARANS.

Tri-hulled kiteboats of the buggy boat style with hulls that are less than full length were the dominant form from 1991 until 1997.  Typically such boats have one steering hull forward in the centre, the others at the rear to each side. Their major advantage is positive turning, very important for kiteboats that  have to jibe to tack.

Of this type, the so called "buggy boats" had the cost and convenience advantages of using standard buggy frames as their structure.

The largest kiteboat I have yet built, a 6m Tri with line winch and full remote kite control (1992) was also of this layout.

The planing-only type buggy boat from 1994, called, confusingly, the kitesurfer is still probably the fastest kiteboat I have sailed on and the only kiteboat that can yet match actual kitesurfing for speed and manouevrability.  Like kitesurfing, it was fast for reaching and downwind courses but weak upwind.

Buggy boat style Tri's lack of water line length relative to overall size costs too much performance, especially in light winds and when underpowered.  They probably don't have a long term future now that the use of linked together front and rear rudders has improved the turning performance of catamarans and trimarans with full length hulls to a satisfactory level.

Trimarans comprising a central hull with outriggers on each side, all full length, do have a future in kitesailing. 

Their biggest advantage relative to catamarans is the practical one of requiring only one set of things like fins, rudders, steering controls and kite flying position.  In larger sizes they also have better possibilities for accommodation.

About their only disadvantage is having to carry one redundant hull on each tack- the one on the upwind side.  This adds to cost of manufacture, is a bit heavier and makes the trimaran wider for docking and transporting compared to a catamaran of the same form stability.

CATAMARANS.

The advantages and disadvantages of the catamaran layout for kiteboats are;

-Good form stability for waves, surf and overpower.

-Excellent speed in displacement mode for good upwind performance.

-Easy transition to planing mode for high speed reaching and running (requires flat bottom hulls).

-but slower turning than monohulls, although about the same as for trimarans and proas.

-and requires duplication of fins, rudders, steering mechanisms, and seating.

For small kiteboats the good form stability of catamarans is particularly useful for getting out thru big surf and also allows larger kites to be used.  Bigger kites boost speed on all courses and, particularly, improve upwind performance, which is very sensitive to lack of pull. Larger catamaran kiteboats also benefit from having excellent form stability, but are not as suitable for living on as monohulls, except in very large sizes for which there are currently no conceivably suitable kites. 

MULTIHULLS IN GENERAL.

Although much harder to capsize than monohulls, when they do go over multihulls are much more difficult to get back up.  After a century of trying various methods, the sailing world has fairly much settled on providing hatch access on the hull bottoms, some facilities for upside down living. and satellite transponders to call for rescue.  The safety record (by loss of life per km) of sailing multihulls now seems to be better than for keelers, mainly because unlike keelers, they don't sink when filled with water.  For multihull kiteboats it should also be possible to rig an outboard motor to use while upside down for (slow) motoring home.

I believe that for kiteboats, the multihull will become the dominant type.  Compared to monohulls, the superior windward performance that derives from the use of generally bigger kites, which comes in turn from their better stability, matters more than every other consideration.  Windward performance is the weak suit of kite sailing so becomes the most important criteria when weighting advantages and disadvantages.  

TO HYDROFOIL OR NOT TO HYDROFOIL?

Hydrofoils have problems in rough water.

Sir Alexander Graham Bell, inventor of the telephone, had a successful hydrofoil power boat just after 1900 and hydrofoils were going to save the world in the 60's and 70's but, after 100 years and millions of dollars of development, powered hydrofoil craft now have no significant role except as lake ferries..

There is a successful, commercially available, hydrofoil sailing craft, the Greg Ketterman designed Tri-Foiler.  These are very fast and a blast to sail but work best on flat water and in a narrowish wind range.  I've heard of various projects to build scaled up versions of these that should be able to handle bigger waves.

Having to deal with intrinsically less heeling moment than comes from sails up masts makes designing kitesailing hydrofoilers easier than sailing hydrofoilers but the great variability of kite pull cancels this advantage. 

Preventing individual hydrofoils from coming out of the water because of the kites uplift is just as difficult as preventing them running too deep and has more serious consequences. 

Nevertheless, hydrofoil kiteboats can work.

Successful small kitesailing hydrofoilers have been built, by the Legaignoux's, by myself, and others.  My experience so far is that they have no overall performance advantages and some disadvantages relative to displacement/planing catamarans.  I have seen, variously, no better top speed, inferior light wind performance, inferior upwind performance, inability to cope with waves and rough water, annoying oscillating transitional states between up and down, and total catastrophe whenever I run aground at speed. 

All these problems (except the running aground?!) should be solvable, and possibly already have been, although going bigger is likely to be the only thing that will help with waves and rough water.

There are about as many possible arrangements for hydrofoil craft as there are people to think of them but the most popular layout is two in front, one at the back.  The front ones are either of the "Bruce foil" surface piercing self levelling type, ladder foil dittos or Ketterman style hockey sticks with surface sensors.  The rear one is usually a "T" foil. 

This layout best suits a trimaran although catamarans are also adapted to this by fitting the rear foil to the centre of the back cross member. 

Hulls are required to support everything until take-off speed is attained and as a safety net when "falling off" the foils- which, because of ventilation, sometimes happens unexpectedly. 

Smaller monohulls are usually too slow to allow sufficient speed for take-off, unless they are of the planing type in which case what's the point of having hydrofoils.  If the monohull is long enough (say 7m or so) to get to sufficient speed in displacement mode for smallish  hydrofoils to start lifting, then they could provide useful top end speed.

HARNESSES, WINCHES AND KITE ATTACHMENT.

HARNESSES FOR SMALL KITEBOATS.

For smaller kiteboats, the harness systems used for other kite traction activities such as buggying and kitesurfing can be used.  The main variants of such harnesses are the hip harness and the back strap.

HIP HARNESSES are similar to those used by windsurfers and for sailing dinghy trapezes and have an upwards or downwards facing front mounted hook which sometimes takes the form of an open sided pulley.  A loop of braided line (called the harness line) that is attached to the kite's handles or bar, passes thru the harness hook.  I favour upward facing hooks because they don't disengage as often when the kite pull is momentarily being taken thru the fliers arms during control movements, but will usually automatically disengage when the flier is being dragged screaming over the rocks during overpowers.  There are harness variations without hooks that have a pull cord for emergency release but many people freeze when panicking and fail to operate it.  It is possible to train yourself to remember to use such panic buttons, if you survive the training period, that is. 

Hip harnesses keep the kite pull low and largely prevent random body movements from accidentally steering the kite, both of which are advantageous in strong winds.

They do limit the range of arm movement that is available for kite control but this is also not a big problem in strong winds.

BACK STRAPS are used with handles (2 line or 4 line) but not with bars.  They are the best system for light winds.  Their advantages are the facility to readily alter the kites pull height and the maximum freedom for kite control they allow.  When using a back strap in light wind, it is possible to control the kite by swivelling your shoulders, leaving both hands free to do other things (like making various gestures at kitesurfers for example).  Body steering becomes a disadvantage in strong winds (above say 30km/hr) when the kite is too sensitive.  Although pull cord releases are possible with back straps the usual release method is to lean forward and let the strap slide off.  Pointy back crash helmets can be a bit of a problem when doing this.

KITE ATTACHMENT FOR SMALL KITEBOATS.

There are various systems that have been used.  The best is just to have suitably positioned hooks on each side of the boat.  The usual harness line (as for a hip mounted hook) from the kites handles or bar is dropped over the downwind hook and takes the kites pull directly to the boat at a point low enough to eliminate most heeling.  For small monohull kiteboats that don't have a lot of heeling resistance, side hooks allow the use of much bigger kites, provided swapping sides. is done during underpowers.

Releasing from side hooks during an emergency requires a pull cord system (spinnaker clips made for yachts are the usual) or taking enough kite tension to allow the harness loop to be slipped out.  In extreme situations it's possible to just bail out and leave the kite and boat to complete whatever sort of mischief they're up to- doesn't always work though, sometimes you get caught up and taken along for the ride.

The side hook system is useable for boats in which the flier's seat faces forward but not with the latest catamaran kiteboats that have alternate sideways facing seating positions.  This is because the flier is occupying the place where the hooks would have to be for reasonable longitudinal kite pull balance.  An answer may be to provide hooks that slide or swing out like an amusement ride seat restraint bar- providing the risk of being trapped under a capsized boat can be mitigated.

WINCHES FOR SMALL KITE BOATS.

Boat mounted winches and indirect flying are not usually used on small kite boats because of the loss of sensitivity.  When loads are low enough to allow direct kite control it is always preferable to do so- with a harness to relieve some of the loads of course.

Wind in/braked out handles and bars can be used with small kite boats for kite relaunching but boat drift speeds are much higher than for immersed bodies (that is kitesurfers) so often don't work satisfactorily.  Maybe a sea anchor would help.

KITE ATTACHMENT SYSTEMS FOR LARGER KITEBOATS.

This is now the key to the entire challenge of large boat kite sailing, the most difficult remaining problem and one that must be solved to a high level of reliability if kitesailing is ever to become more than just a fringe activity for a few obsessives.

A SYSTEM THAT DIDN'T WORK.

RADIO CONTROL was a system for which I had high hopes in 1990 because a radio controlled kite would require just one line, immensely simplifying winches and things at the boat end.

Various prototype systems based on model aircraft radio control units were built but although steering was satisfactory, it was very "2 dimensional"- when controlling kites using 2 or 4 lines, fliers do far more than just steer the kite left or right.  By example, even for 2 line kites, a turn to the right can be accomplished by pulling the right hand line in or by letting out the left hand line and every combination in between.  The kite will respond differently to each, and this level of fine control is often the difference between kitesailing and swimming.

Undoubtably radio control could be developed to the required level of sensitivity but there was another problem: weight.

For a 5 sq.m. kite weighing 500gms, the receiver and servo's added 250gms and a battery good for 1 hour of flying added a further 500gms.  No matter where this was distributed over the kite it stopped it flying satisfactorily.  Of course there are many possible ways to reduce this weight, the main one being more balanced control surfaces to reduce servo loads, but even 250 gms of battery, servo and receiver  is probably too much for this size kite.  Nor is it a problem that reduces as kites get larger, the servo's and receiver weights would stay fairly constant but the battery scales in proportion to kite area, and 1 hour is not enough anyway.  A wind powered generator would weigh about the same as a ½  hour battery but would still require battery back up so provides endurance but doesn't fix the underlying problem.

I don't believe that these problems are necessarily insurmountable but decided after the above tests were made, to look at other options for a while.

ANOTHER SYSTEM THAT DIDN'T WORK.

Like most kitesailing hopefuls, my first larger boat kitesailing experience came from using the biggest kite I could find (in this case a re-rigged to two line, 15 sq. m. sky diving foil) with an unmasted sailing catamaran.  Although I never did manage much upwind sailing and had a terrifying crash (described in "Buggies Boats and Peels"), there seemed to be potential.

The next step was to try out various remote control kite flying systems on smaller boats.

From these experiences, in 1992 I built a 6m trimaran of the one steering hull in front, one fixed hull to the rear at each side layout- basically a very oversized buggy boat.

It used two line kites, usually a large delta that, by current standards, was a pig to fly.

The kite flying was via a winch, brake and steering wheel, (rather like a ships wheel) which allowed full pull-in and let-out even while controlling the kite.

To minimise heeling, the kites lines fed thru a longitudinal boom, pivoted at the front and free to describe an arc laterally.  There was a sliding car on this boom which set the fore/aft kite pull point.

For launching and relaunching there was a spring loaded gantry system above the boom to hold the kite up when it was winched in. 

This never worked very well as the kite persisted in twisting around and doggedly hanging upside down instead of launching.  To get started we usually had to resort to a "team" launch; lines out, some people to hold the boat back, others to launch the kite.

It was incredibly difficult to keep the kite up; the longest ever time between crashes was just a few minutes and many attempts lasted less than one.

The problem was that variable creep in one line compared to the other as they wound on and off the winch drums caused the centre position on the kite steering wheel to vary by 20 degrees or so either way.  I would have thought that any reasonable kite flier could easily compensate for this but it proved to be nearly impossible.  As a training aid we even flew the kite while driving around a big open paddock in zero wind, with the boat and flier on a trailer.  Practising by flying in these conditions definitely helped but it was clear that the level of kite control was never going to reach the standard required for reliable kitesailing.

Even when the lines were registered exactly to the steering wheel by cutting out the winch function, flying was very difficult.

This experiences demonstrated just how difficult it was going to be to develop a sufficiently sensitive kite control system.

1993 TO 1999 PROGRAM.

In 1993 the 6m Tri. went out to the long grass and took up new duties as a chook perch, for which it has been very satisfactory, and I went back to basics:

-to develop easier to fly and more reliable kites,

-to develop a better launching system,

-to get as much on the water kitesailing experience as possible on smaller boats.

-and to figure some way to attach the kite to the boat with pull-in and let-out while retaining controllability.

By 1999:

-kite ease of flying and reliability has improved enormously,

-motor launching is very promising, an unexpected but practical solution.

-6 more years of building and sailing small kiteboats has refined theory and practise to a hopeful level.

-and progress has been made in developing attachment and winch systems for larger kite boats.

As was learnt in 1992, reinforced by every subsequent experience, any barrier between the flier and kite, even passing the lines through a set of pulleys, causes serious loss of controllability.  However, kites have become so much better that there are now conditions, like strong smooth winds, when kitesailing can be satisfactory even with some loss of control sensitivity.

If necessary we can also trade off some kite performance for more reliability while attachment and winch systems are being developed further.

The goal is; 'all winds, all courses, all seas', but, by the 'crawl before we can walk' analogy, progress may come from first trying; 'some places, some times and with a rescue boat standing by'.

CHARACTERISTICS REQUIRED BY USABLE ATTACHMENT SYSTEMS

From the RC experiments, the 1992 trials, and other experiences, for effective control of the kite the flier must have at all times:

-An easy reference point by which to judge relative line lengths. 

-"Feel", that is some measure of the kite's overall pull and the tension on each individual line.

-Full choice of control movements; pull in, let out, and brake (4 line kites) and in all combinations.

-Clear view of the kite.

For any system to work it must meet these criteria. Currently the best prospect is also the simplest: 

THE GAME CHAIR

Basically the flier sits in a swivelling chair that always faces the kite.  The kite lines, 2, 3 or 4 go direct from the kite to whatever type of bar or handles the flier chooses, and then pass inside the bar/handles by pulleys to emerge at the points where the harness would usually be fixed.  From here they pass either side of the chair along compressive struts to points about 0.75m apart on the winch platform which is behind the chair and pivoted in the vertical axis for primary steering. 

Foot controls set the winch for "hold", "let out" and "pull in".  The "pull in" function could be manual or electric powered or just spring loaded like an automatic dog leash. 

This system is the most direct and would have the best "feel" of any approach I have seen or thought of. 

It is suitable or could be adapted for most types of kites and launching systems and would work particularly well with the motoring back launching option. 

A limitation may be the size of kite (hence the size of boat) that could be handled, as muscles are still its primary power source for kite control, but control would probably remain possible up to even a few hundred kilograms of pull providing this wasn't the average.  Flying a kite big enough for an 8m long 2 or 3 person boat is certainly practical.

By placing the chair on a pivoting arm the heeling moment can be reduced to the level required for any of the hull options.

KITEBOATS FROM PETER LYNN LTD.

We've been selling small kite sailing boats since 1990.  Until 1997 these were of the "buggy boat" type with 3 hulls and a buggy frame.  Four different versions were made.  The 1994 model had short wide planing hulls and the 1996 model had facility to transition from displacement to planing when there was enough pull.

Now we offer two different styles, both faster for less pull then the buggy boats.

One is a single person monohull available ex stock from Peter Lynn Ltd in New Zealand and Vlieger Op in Holland and the other is a single person catamaran that is built to order as required.

SINGLE PERSON MONOHULL KITESAILING BOAT.

This has a 3m long, 0.8m wide planing hull, roto moulded in polyethylene with 4 rudders, 2 in front 2 at back, all steering, foot operated, and a pit for the flier to sit in to get the kite pull and fliers weight low for stability. 

Easily portable (in the back of a van or on a car roof) and highly manoeuvrable (because of the flat bottom and opposite steering rudders), this boat works best in lakes, harbours or sheltered water but can be used in surf up to about 0.5m after a bit of practice.  Generally it requires a kite of about 2/3rds the size that would be used for kitesurfing in the same conditions.  Using a bigger kite than this usually results in capsizes or getting hauled off- although it is often possible to get back on again if the kite remains up and always possible if the kite is relaunchable.  Even with the smaller kite it has good speed in light to moderate conditions and goes to windward very easily compared to kitesurfing although when the wind gets up kitesurfers are faster. 

It is possible to fit harness hooks at each side of the seat to take the kite pull directly to the boat.  These allow the use of a bigger kite by reducing heeling but work best when flying with a bar (4 line or 2 line) because standard type 4 line handles get out of reach, even with a short harness loop.  Hooks are not supplied as standard equipment.

Until the techniques and limits are learnt, new users tend to tip out when they get overpowered.  The main principle is to keep the handles low when experiencing gusts.  This sounds easy but is counter-instinctive for most kite fliers.  With standard type 4 line handles, placing the tops of the handles together with the brake ends on opposite sides (called butterflying), allows both handles to be forced  down to deck level and this reduces heeling to a minimum.  If you have to think about this before doing it, it's going to be too late.

We've had one customer who thought the hatch was there so that the boat could be partially filled with water for stability.  Our Dutch friends have sworn me to secrecy as to the nationality of this customer.

When jibing, the most secure technique is to turn with the kite, not before, not after.

For getting back on after tipping off it's best to have a kite and harness system that allows at least a few seconds of hands free flying.  If you're not attached to the boat with a leash it is still usually possible to park the kite up while the boat drifts passed and then get on again. For going out thru biggish breaking surf, keep some speed up and hit it straight on or try to miss the breaking bits.

For coming in thru biggish breaking surf there is only one technique that works; speed; never let it catch up.

Going small boat kite sailing in a place where the winds can carry you away from land is not safe unless there is an alert rescue service.

If you dunk the kite and can't relaunch, roll the lines up, fold the kite, sit on it and paddle home.  In the case of a C Quad its best to take a bag with you (in the hatch provided) because it's very slow paddling along with the kite trailing in the water behind- and the bridles catch on everything.  Carry a paddle, it easier than using hands.

SINGLE PERSON CATAMARAN KITESAILING BOAT.

Our Catamaran is 3.7m long, 1.6m wide, with 2 rudders forward and 2 at the rear, all steering and has displacement/planing hulls. 

The flier faces the kite rather than the front of the boat and there are alternate seating positions for opposite tacks.  This makes for very secure and comfortable sailing even when one tack is held for an hour or more.

The hulls are fibreglass, hollow, although some have been built as glass over foam.

The frame is stainless steel tube and can be made so as to dismantle completely for fitting into a single 3.7m long, 0.5m diameter bag with the hulls.  They have been carried as air travel luggage at no extra cost. 

Usual transport is by roof rack (fully assembled).

Although the catamaran has about the same speed as the monohull for the same kite pull, its extra form stability allows the use of a kite typically 30% larger so it is usually faster.  Because of this and slightly greater

waterline length its upwind performance is ahead of the monohull and often matches conventional sailing dinghies.

Its turning (4 rudder), is not as tight as for  the monohull but excellent by multihull standards.

Stability in surf is very good, although breaking waves any bigger than about 1m from behind are exciting to say the least.  The waves shown in the picture are interesting but survivable.

There is also a tendency for the flier to not land back in the seat when the boat leaps off big waves.  The only answer we've found so far is to leave the kite to fly from the harness and hang on to the boat with both hands, but at times like that concentration is often elsewhere.  This boat is large enough to mount a small outboard motor; for safety, for when the wind dies and for motor relaunching.  Motor relaunching is difficult for one person though because there are never enough hands to spare for unhooking snagged bridles, getting the kite to sit the right way in the water, and for operating the motor.  However, this system was a new idea late last (Southern Hemisphere) season so probably I just haven't worked out good techniques yet.

Overall, the catamaran's inherent performance and reliability are good enough to have me contemplating some extended cruising during the coming summer- I just can't wait!

WHAT'S COMING?

What new kitesailing things are coming next from Peter Lynn Ltd?

SMALL KITE BOATS.

The monohull and the 3.7m catamaran are both state of the art designs, the monohull from 1997 and the catamaran 1999.  Each of them has a niche and nothing that has been learnt since their development would change their designs in any  significant sense.  The goal for this season is to explore their limits.

Some minor changes coming up;

-Stainless steel fins for the monohull (much better for running onto sand and rocks), 

-Maybe optional bigger fins for the monohull for better upwind in marginal wind, trading off draft.

-New hull moulds for the catamaran to improve production and reduce weight.

-Some form of swivel or slide-out seat restraints for the catamaran, perhaps incorporating harness hooks.

-An optional motor mount for the catamaran.

-A luggage rack for the catamaran- for lunch (and spare kites).

KITES FOR SMALL KITEBOATS.

Likewise, although incremental development and work on new kite designs never stops, our current designs are new from 1997 (NGen) and 1998 (C Quad).  Their full potential with the small kiteboats has yet to be fully developed, especially the C Quad.

LARGER KITE BOATS AND KITES.

7M CATAMARAN.

Work has started on a larger kiteboat.

-It is to be a 7 to 8m long, 2.5m wide multicrew catamaran with a "Game Seat" kite control system.

-This seat will be on a rear pivoted damped arm that will swing to the hull nearest the kite.

-Boat steering will be by the flier via a foot bar and linkage to front and rear rudders on each hull.

-It will be set up to facilitate motor launching by having motor controls duplicated at the fliers seat.

-And have space to carry an inflatable Zodiac style dinghy for emergencies.

Initially the kites for this boat will be scaled up C Quads but other designs are contemplated.

The goal, this iteration or later, is a fast self sufficient reliable kiteboat for inshore and some coastal sailing.

At least I'm going to find out for sure whether I've learnt anything since 1992.

But even if I haven't, tilting at windmills is scheduled to continue.

Peter Lynn, Ashburton New Zealand, July 27 1999.

DEFINITIONS.

L/D              For kites, the ratio of Lift force generated to appropriate Drag forces (kite and lines).

                    For hydrofoils, the ratio of lift force generated (vertically) to appropriate drag forces.

                    For hulls vertically, the ratio of the weight supported to the approp. hull drag .

                    For hulls horizontally, the ratio of lateral force generated to the approp. hull drag forces.

                    For fins etc, the ratio of lateral force generated to the fins drag forces.

                    For boats overall, the ratio of weight supported to the sum of all (water) drag forces.

HDA           Hydrodynamic drag angle, degrees. Arc-cotan of side force resisted/total hydrodynamic drag.

ADA           Aerodynamic  drag angle, in degrees.  Arc-cotan of the kites L/D.

VMG          Velocity Made Good. (to windward). Component of speed in the upwind direction.

C of P          Centre of Pressure.  Point at which aerodynamic or hydrodynamic forces act.

Lift Coefficient.          CL, Dimensionless, lift per unit area for a (air)foil at given apparent wind speed.

Angle of Attack          Degrees, angle of foil to flow direction (water or air).

Underpower               For kite traction, having less than the optimum pull.

Overpower                 For kite traction, having more than optimum pull.

De-power.                  A traction kite's ability to reduce overpower, manual or automatic.

Max/Min pull ratio     The ratio of the kites max. pull to its min. pull during any given manouevre.

True Wind.                 In Km/hr.  the actual speed of the wind over the ground or water.

Apparent Wind.          In Km/hr. the velocity of the air stream impinging on the kite.

Figure Eighting.         Manouevre used to increase a kite's apparent wind speed, and hence pull.

Keeler.                       Yacht, monohull with a ballasted keel, usually largish.

Hull Speed.               Nominal maximum speed imposed on displacement hulls by Froude's law.

Cavitation.                When the absolute pressure near a foil drops to zero- a "bubble of vacuum".

Ventilation.               Air entrapment in low pressure zones near foils that destroys their function.

Upwind/Downwind   Ratio of times taken each way on an upwind-downwind course.