prior to the foiling revolution, development in the class had stagnated. the hungry tiger was an unbeatable hull and the australian sleeve luff rig superior in most conditions. we were becoming a one design.

now all that has changed. three top quality builders are producing competitive designs. foils, control systems,hulls and rigs are all being chopped and changed in a rapid quest for the fastest flight. credit must be given to the perth foil pioneers brett burvill and john ilett for taking the technology to this point. the interesting (and encouraging) thing is that development is now international. ideas from the UK seen at garda have found their way back to australia and vice versa.

so what are the design developments and what do we know of their potential? most of the current innovation is targeted at one of two goals: more stable foiling and less drag.

thanks to rohan veal and scott babbage for reviewing developments at the australian nationals.

pretty much the whole boat is being re-evaluated. here we look at each part in turn...incidentally, if any yacht design students have research papers about moths or relevant to moths, int-moth.org.uk would be happy to publish them in pdf format. adam may will review papers for relevance.

foils
unsurprisingly foils are the centre of attention. at the europeans at lake garda, linton jenkins (fullforce) turned up with a beautiful set of foils with elliptical ends. adam may had similarly modified his fastacraft set. the latest foil design from foil pioneers, fastacraft for the prowler 4 now also has eliptical wing tips. scott babbage's prototype hungry tiger 2 also has eliptical foils from phil stevenson's mould. the thinking is to improve the efficiency of the end section of the foil therefore reducing drag. no noticable benefit has been observed but generally it makes sense.

fastacraft foils have kevlar hinged flaps on both foils while the fullforce and stevenson foils have carbon hinges.

scott babbage: The (hungry tiger 2) foils are built from Phil Stevenson's mould with different sectional shapes to Rohan's previous foils. They're using tapered tips and hinges (rather than kevlar) mounted flaps. The centreboard doesn't have as much forward rake as Rohans. The foils were first-generation prototypes, with the order being for strength & durability. They're subsequently heavier than the hollow pre-preg equivalent. They won't be breaking any time soon.

you'll have to visit the geek sites if you want to know about foil sections but there are subtle differences and you can feel them on the water. the ride can be quite different. our impression is that the fastacraft system requires relatively more input from the sailor and the tiller twist is an essential part of the process. comparatively the fullforce system gives an automatic pilot ride with the tiller twist having a less dramatic effect (that's just our impression. if you don't agree let us know).

there's been a lot of experimentation with foil lengths for example chopping bits off the front wing and sticking them on the back. the 'standard' seems to be around 850mm front and 650mm back.

another innovation from linton was dispensing with the rudder flap altogether. he seemed able to control ride height pretty well with just a front foil flap and body movement.

finally there's experimentation the location of the foils to the hull. rohan veal: I think we have all agreed that the foil’s leading edge should be around 1650mm from the transom. I could be wrong though. Basically all the new boats (prowler 4s) will be in this position, as we are not convinced that moving them forward or backwards is beneficial, but more tests will be needed. Certainly the 500mm outriggers make a big difference.

scott: - The gantry I used was a 400mm carbon/foam box structure, since the tiny transom made it difficult to engineer something that wouldn't break. It did make for a smoother transition to foiling, but filled up with water at times as well.

the gantry has been another focal point. with twenty boats taking to foiling in the UK in the spring of 2005 (with varying foil geometries), it quickly became clear the the relative angles of the two foils is critical. too much lift at the back and you can't get launched - too little and you jump out like a performing seal. adam may fixed this for the UK nationals with an adjustable tubular gantry (see pic)- another idea making its way back to australia post garda. 500mm is the maximum gantry length allowed by the rules. the thinking is to get the foils as far apart as possible and improve fore and aft stability. but at the australian nationals, chris dey bolted the fastacraft rudder to the transom of his hungry tiger and reported no problems. are gantries for wimps?

here's some more info on foil development provided by phil stevenson:

phil: Scotts foils from my mould are 900 fore and 700 aft. The curve at the tips is only on the leading edge. The TE is straight. His hinges are stainless steel piano type, heavy but they work OK.

The section was supposed to be the same as John's but it just got a touch thicker in the mold construction. I made the mould with generous advice from John given over the time of the Black Rock worlds. We had not used it much when Thorpey made Scotts set. He did not want any failures so he basically filled the mold with carbon. They are strong! I have since made some lighter mouldings but have also broken some. Wet layup is obviously not as good as pre preg. but the one piece moulding does seem to help.

Chris Dey used an Ilett CB foil and a rudder foil from my mould. It has no flap or hinge, Chris and I both use a transom mounting and a tilting mechanism developed by my son Andrew which moves the whole rudder with tiller extension twist. Chris' only problems were when he ran out of adjustment.

Rohan and Robbos new foils are highly tapered and about 950/750 spans. They have about the same area as the old model square tips with 800/600 spans as used by Steve, Luka, Craig and Pete. These guys, plus myself are still working out angles of attack and consequently getting varied results. My foils are both 900 span with the front hinge made from untearable window tinting film.

Thorpey is presently considering and costing foiling conversions for Les and Ben Croker. While Andrew Sim and Ian Ward (who bought Mic Boode's Tiger) are also keen to get set up.

Allan Goddard, and Greg Wise both had unfinished foils at the nationals and Geoff Kitchen (Jethrow) will get onto his when he fixes his Torpedo hull. Bruce McLeod broke his Centreboard and AMAC broke two gantries, trampolines and assorted linkages, but he is just tough on boats.

We had 11 foiling boats this year and there should be a 50% increase in foiling numbers by next year. But our NSW champs over traditionally light wind Easter are at Nothbridge behind the hills in Sydney's Middle Harbour and it is not likely to be foiling weather.

control systems
the two main suppliers differ most here. the originals from fastacraft feature kevlar mounted flaps with a silicone rubber fillet in the top (low pressure) side to smooth the join. this provides some resistance which is overcome by a robust cable (borrowed from powerboating)and glass rods inside the vertical section of the foil. the low resistance carbon hinged fullforce system uses carbon rods to link wand to flap and inside the foil. si payne is believed to be trying an hydraulic cable on his new prowler 4, presumably sourced from a mountain bike shop.

wand loction has temporarily fixed at the bow although john ilett experimented with an underhull wand in 2004. rumours from weymouth suggest the wand may not be resting in peace just yet.

hull
the mantra here is 'less is more'. since the hull is now only required to perform light wind duty, the smaller and lighter it can be the better. this promotes early foiling and cuts wind resistance when up. the mistress 3 and hungry tiger 2 are particularly tiny. hull weights below 10kg are standard now. innovation isn't confined to the professionals. rohan: Jethrow rocked up with a brand new home made foiler, that looked like a torpedo shaped hull. However structural problems meant that the boat didn’t see much water time.

scott: The boat was put together with foiling in mind, so we've reduced the freeboard significantly and minimised flare. We've cut a lot of material out of the hull and used a custom deck, giving us an all-up weight of just over 9kgs.

jethrow's torpedo looks like it merits a design profile of its own. Jethrow: Unfortunatly it's too small for my immense bulk so Mk.2 is on the drawing board at the moment

rig
rigs are perhaps comparatively neglected at the moment. most people are happy to go along with the MSL development cycle and the excellent brett burvill (windrush)mast. andrew macdougall of KA sails refines his sail design at least once a year so things are hardly standing still. sooner or later another sailmaker's going to try to match the dominant MSL and heat things up some more.

the class has clearly entered a period of rapid development. more time money and ingenuity is being poured in than anyone can remember. the order books of our main builders are said to be very healthy so it appears that far from scaring off new members, the arms race is in fact driving growth in the class. int-moth.org.uk welcomes comments and contributions. if you disagree with anything here or have something to add email us and it will be included on this page. must go - have a meeting with my bank manager...