January 2007

Newsletter, Jan '07

"Twas the night before Xmas and all through the house, nothing was stirring not even a mouse—".  Well, it was the night before the night before, and there was quite a bit of stirring and carrying on going on (it's being my 60th and all that), but near enough.

And then Osama arrived.

A birthday present from Andrew and Kathleen Martin-Beattie from England, Osama is a large and not entirely male goat.  'He' survived the journey well but seemed a bit apprehensive -possibly something to do with the suggestive birthday greetings note they'd attached to him.

While appreciating this present and the thoughts behind it, unfortunately my travel commitments for 2007 do not permit accepting such a responsibility, so we are currently arranging for his return to Andrew and Kathy where I'm sure he can do sterling service in weed control in their back yard- oh and he likes eating kites too, so won't ever have to go hungry.  Fortunately Paul and Natalie Reynolds (kiteflying friends from England) arrived for a surprise visit yesterday and are currently being inveigled (there's a "pet" category for baggage) into taking Osama back to A and K with them when they return to the UK after the Nelson festival late this month.

In the meantime, Osama was pressed into service during our Xmas day "Great Race" pulling a kite buggy -see photo- then released into the jungle behind our house.  This place is goat heaven, and he's very happy there except for lack of goatish companionship.  The jungles only other denizens, that we know of, are four geriatric chickens.  Perhaps he'll learn to sing a different song.

The name Osama is on account of we aren't exactly sure where he is now, he may be still there or he may not, hard to tell really.  Is he Osama bin Lost or will it be Osama bin Fownd?

And now so you know I haven't been completely neglecting kites on account of this new found- err lost- friend:

It's being New Year and the time for resolutions and all that, I've just corrupted the process by breaking one before I'd even really made it.

During '06, I definitely and conclusively decided that developing new kite sailing boats is a waste of time until kites catch up, and dedicated myself to doing only kite developing until this happens.  So, I've just spent the last month building the definitive kite sailing boat.

It's a long thin monuhull, (7.5m long by 0.47m wide) and I think it might become the model for ocean going kite powered craft of the future.

The ideas behind it now seem clear and inevitable, granted that as it's taken 20 years to gestate they weren't always that glaringly obvious.

The enabling feature is keel stability- it's centreboard and rudder are weighted so as to make the boat self righting.

This approach for kite sailing boats has generally been rejected because it's "impure" and because the main point to using kites rather than conventional sails is that as kites can be attached so as to eliminate heeling, why should a keel be necessary?

For performance orientated conventional sailing boats, the keel can be up to three quarters of the total weight of the craft- as much as 12 tonnes of lead hung below just 4 tonnes of super light hull mast and rigging.  Their keels have to be heavy because the wind load trying to tip such a boat acts at the sail's centre of pressure which is likely to be 10m's up a 30m mast in the above case.  For a kite boat however, the kite's pull can be applied at the underwater centre of lateral resistance.  In this case there is no heeling moment from wind forces, so the keel weight needs only be sufficient to make the hull self righting and- even allowing for unprecedented reserves of stability- can probably be much less than a quarter of the craft's total weight.

Once this is realized, the other advantages that monohulls have over multihulls (currently the anticipated choice for ocean going kite sailing) make the choice a no-contest.

*The weight of the keel for a monohull kite boat will be much less than the extra weight required to have two or three hulls and their connecting structure.

*Such a monohull could have much greater water line length than an equivalent multihull, so it's speed for the same kite pull will be much higher - because the major component of hull drag is proportional to the square root of the water line length.

*The aerodynamic drag (superstructure profile) of a monohull is much less than that for multihulls-, which directly translates into superior upwind performance.  Aerodynamic drag imposes the major but often unrecognized limit on upwind performance for sail powered craft of all types. 

*Monohulls are structurally stronger (the critical structural elements for multihulls are the cross members and their attachment points at the hulls) and can hence be lighter- and MUCH cheaper for the same size.

*Accommodation is all in one space and for the same total volume when compared with a multihull will allow greater width and more headroom. 

*Multihull form stability make them resistant to tipping- but when the do capsize, and they do, can't be recovered.  Monohulls can capsize in extremely adverse conditions- but then they come up automatically and continue.

This model has the features that I expect will become standard on larger monohull kite powered craft.

They will have forward and trailing rudders linked together to turn in opposite directions.  This maximizes turning effect and leads to optimum maneuverability but is essential for another reason: if only one rudder is used, when a sudden turn is initiated, the lateral force applied to the boat by such a rudder will cause the boat to tip over because it applies at a point well below the bottom of the boat.  Having forward and rear opposite turning rudders completely neutralizes this effect.

They will have a kite attachment system that applies the kite pull through the craft's lateral hydrodynamic centre of pressure- a point that is significantly below the bottom of it's hull.  The system on this model does this even when the kite is flying very low; it's optimum position for best upwind performance, and an essential feature.  The linkage used to do this is the most practical one that I have been able to think of that does this- actually so far it's the only such linkage that I know of.

The hull length/width ratio will be in the 10 to 20 range; this model's is 15.  This is for maximum speed in the lightest winds and to minimize slamming and discomfort in wave conditions even at high speed. 

The hull will be wider than it is deep- approximately 2/1.  This is to minimise aerodynamic drag by keeping the above water line profile to a minimum.  For a 60m long version scaled from this model, hull width would be 4m and headroom 2m.

The hull on this model came from a planning boat, so is not exactly the shape I envisage as ideal- its major dimensions are not far wrong though.

There'll be photos of its first test as soon as I get useful wind.

Otherwise, Peter Lynn Kites Ltd are really getting into kite sailing this season- KiteCat orders and enquiries are at unprecedented level, and there is major effort going into re-jigging production to meet demand. .

They also have a new/old kite boat that may now be going into production.

What was the three hulled planing style "Kitesurfer" in the mid '90s now has four hulls and is called the "Quadsurfer"- it goes like stink!  See video soon to be posted on You Tube.

Also, their single line kite launching platform for towing behind powerboats and Jet Ski's is completed and awaiting its first test.

Peter Lynn, Ashburton, Jan 1 '07, enduring our coldest and wettest spring and summer on record!