February 2012

                                                    BACK TO THE FUTURE.

In last month's newsletter I speculated on maybe having another go at making kite sailing work; because it's unfinished business of course (25 years of serial failure so far), but also in an attempt to escape the increasingly stifling attentions of all the toys that I seem to have 'been adopted by' in the last few years (veteran cars, stirling engine boats , vintage jet engines, large stationary motors and ever bigger ride-on lawnmowers for example).

Specifically, I (still) have in mind the challenge of making kite powered boats competitive with conventional sailboats for course racing- including trans-oceanic.

Kites have two major advantages over conventional sails;

The first and most significant is that they can be rigged to a boat's hull so as to cause no heeling.

Anything bigger than a dinghy sized monohull sail boat requires a weighted keel to keep it up the right way up against the sail's attempts to tip it over.  Multihull sailboats use widely separated hulls to provide a stable platform that can resist sail heel- and pay a considerable aerodynamic drag price because of the above water structure this requires.  And in larger sizes (above 8m or so), when tipped, they stay upside down until rescued.

The second advantage that kites have is that because the kite is not rigidly connected to the boat; it can fly at higher altitude where wind is stronger and more consistent, and it can be 'worked', that is, looped or figure-eighted to develop much more pull for it's size than is available from a fixed sail.  'Working' the kite comes at the cost of some reduction in available upwind course though, and when a boat is sailing faster than the true wind speed (which all fast and efficient sailboats can now do), every course is 'upwind' from the perspective of the boat (called apparent wind).  This advantage is therefore mainly useful when turning and accelerating.

But an obvious barrier is kite launching.

Not having a mast to pull the sail up on, and that will keep it up when there's no wind, kites have to be launched, and then kept in the air.  Various launching systems are used:

At the most basic end, some LEI fliers just throw their kites over the side, let them drift downwind then launch them off the water.

A more sophisticated system is to have a short launching mast and a winch system. The kite is launched at the pole tip then let out to flying length by the winch.  The accompanying Sodebo photos show this in use.

And of course, lighter than air kites can and have been used.

But I favour using a pilot kite system (which has a venerable provenance, having been described by George Pocock in 1827).

This is because making winches that accurately keep four or more separate lines in register while their tensions vary widely as they are let out and pulled in is very difficult- and the lines still tangle and snag in dangerous ways while this is being done anyway.

And because it's impossible to keep helium from leaking out of lighter than air kites- and far too expensive to keep re-filling them.

With pilot launching, a small stable single line kite is hand launched, let out to stable altitude and then used to lift the traction kite up (out of the water if necessary) to it's flying altitude.  See '03 photos.

And then there's the light wind problem.

When the wind is below 5km an hour, it's not possible to usefully fly any current traction kite, while competing boats with conventional sails can still drift, getting slowly but inexorably ahead.

Even worse, when the wind is wobbling around between 5km/hr and 15km/hr, as it often does, these same boats will rapidly disappear over the horizon, while the kite powered boats will be fishing their kites out of the water, into which they will fall every time the wind drops to 5km/hr for more than 30 seconds or so.

The added difficulty of launching wet kite is especially annoying.

This is not good fun, and nor is it a good look for bored sailors on conventional craft who might otherwise have been contemplating making the change.

And this, I think, is the essential reason why kite sailing has not yet become established.

Or maybe it's just that there hasn't yet been sufficient time and effort put in to making it happen- George Pocock's seminal kite sailing journey on the Bristol Channel with family and friends was less than 200 years ago after all.

So why should I think the time is now right for the breakthrough attempt (apart from the niggling thorn of unfinished business, and that I currently have time and means)?

One reason is that pilot kite launching really does work; requiring a bit of stuffing around, and not always at the first try (if the kite being launched bow-ties for example), but eventually it always does, and no doubt time and refinement will lead to further improvement.  Spinnakers used by conventional sailors are not always quick and easy to launch either, and they're well accepted.

When we did our main series of pilot kite launching tests in 2003, I used a complicated system by which, by pulling a looped line in 30m or so then unhooking one end of it, the pilot could be released from the launched traction kite and retrieved.  I now use a simple hook on the pilot line which engages a loop on the traction kites leading edge.  After launching the traction kite, the pilot line is pulled in, releasing this hook and allowing retrieval of the pilot.  This is so simple and easy that it was never going to happen until the same job had been done in a complicated and messy ways for years first.

Another reason is that a few years ago we showed conclusively that NASA style single skin kites are surprisingly better upwind than I expected theoretically. 

NASA's pull very strongly for their size, but don't fly at a very high angle.  However, they are the best light wind traction kites there are; will fly in almost nothing, especially when made of now available lightweight (like 15gm/sq.m) fabrics.

We found by repeated comparative testing using two identical kite cats, that a 20sq.m NASA would always beat a 20sq.m Arc around any upwind/downwind course up to at least 15km/hr true wind. 

Which can't be true but is.

The technical term for this is cognitive dissonance- things that our rationalising brain structures cause us to ignore because they don't align with our general world view.

But facts are facts whether we agree with them or not, and this is a fact that I've begun to like so much that in this case I'm going to change my mind and accept.

Because it's a partial answer to the light wind problem for kite sailing.

The rest of the answer is maybe to chooses windier places to sail. 

But the main reason is that I now know it's possible, because it's already happened.

Have a look at this link: http://www.youtube.com/watch?v=l29gGKzmlkU&feature=related

It's a kite boarder conclusively beating a hydrofoil equipped Moth (conventional dinghy sized sail boat) in a series of upwind-downwind races.  Astonishing!- and not least because hf Moths, for their size, are as fast as anything else on the water.  Granted, the wind and waves were fairly ideal, but on the other hand, kiteboarding is a new sport with neither the kites, boards or boarders anywhere near the peak of their development as yet I would hope.

And, kite boards, though being desirably minimalist as sailing craft (like they can be taken to the water on public transport if push comes to shove) do pay quite a performance price for being short and small.  Longer larger craft have inherently less drag (especially aerodynamic), so should be faster still.

The game's on then: Motive, means and opportunity.

But as the saying goes: If you do the crime you have to do the time- and I had been rather looking forward to a peaceful retirement playing with all my toys.

Hmmmm.

Peter Lynn, Ashburton, January 31 '12