Foiling – Forefront vs Fakes

Who is Foiling and who is Faking. Where is the real technical development.

Trickle up or Trickle down?

First a glimpse of history before we see who is foiling and how the Moth group solved all the problems. Yes … all of them. America’s cup just leaches off this amazing success.

It is Trickle Up … not  Trickle Down.

three moths Foiling-Week-2017-Garda-96877

They make foiling look trivial.

moth worlds start 2017 foiling

Forget the Americas Cup boats … they just borrowed the Moth tech and threw a lot of money and complication at it. And didn’t even go about it in a sensible way.

They are even scared to go out in less than 10 knots of breeze because the America’s Cup (AC) boats look so bad. The moths foil in 4 knots of breeze … because they have to race in whatever conditions are there for  their Saturday any/or Sunday club racing. The AC boats will never improve to produce full range performance because they are not required to race in those conditions.

What the America’s cup boats control with all those guys pumping away and sophisticated microprocessor controlled hydraulics .. the moths do with a twist of the wrist.

America’s cup is sledgehammer to crack a walnut.

So who is foiling and who is faking?

A quick survey of some famous foilers

Ok … we’ve all seen old photo of foiling boats.

Monitor in 1957. Claims of 40 knots, but in the light of truly efficient modern foilers it seems likely that this was an overstatement  by a factor of close to 2.

There’s no way something with this much foil drag was going to sail upwind

monitor sailing hydrofoil

From Speed Week we had Icarus from the brilliant Grogono brothers. It topped out in the mid 20 knot range over the measured 500 metre course at Weymouth speed weeks in the ’70s. Couldn’t sustain very well on foils except for  the angles it was designed for.

(Michael Aeppli, more about him below with his Quant 23 foiler, contacted me and pointed out the measured speed for Monitor was about 27 knots – and he made the suggestion that the 40 knot figure might have been an overenthusiastic journo scribbling down the apparent wind figure)

Simple light punches above its weight. The other thing is though Mayfly didn’t have all round performance, it was easy for people to sail as opposed to the other projects of the time.

Mayfly foiler .. who foils and who can't: storer boat plans

The remarkable Mayfly, from the same era. Designed by a boat modeller who didn’t know how to sail. It was just about as fast as the much more complicated Icarus. The Icarus team tried to leverage Mayfly’s tech but complicated it so much with their heavier and wider Icarus they only managed a moderate speed increase.

These were all necessary steps.

But they were all completely outclassed for one reason.

The above boats were all just sailed a few times for specific events.

It took the Moths, initially the work of the members of the Seaforth Moth Club in Sydney to add the secret ingredient …

Weekly racing in all conditions

20 years of weekly club racing leads to THIS …

Moths move towards more and more minimal boats in search of performance.

The Moths traditionally had two design streams.

The UK preference was for skiff moths with pointy bows. Here one of the main designers and builders John Claridge.

And the Australian Scow moths with their strong wind forte.

lightweight simple plywood SUP - stand up Paddleboard -

The Moths have restricted sail area and mast length. But they have no minimum weight or maximum width.

So as time  went by they evolved to lighter and lighter boats.

Weights of the scows came down to under 40lbs for the hull … all built in ply.

These weights were achieved progressively with a few pounds shaved off each year.

Finally the Brits had a breakthrough. Super skinny moths about a foot wide.

Moth lowrider - are chines draggy -

When they appeared I watched them racing against the conventional boats. The narrow boats would look pretty slow and ungainly. Then they would get a nice gust and in what seemed like a few breaths would suddenly be half or  three quarters of a leg ahead. Then they would look ungainly again.

But  over time … with all the brilliant minds collaborating, sharing information and racing two three times a week development was fast and the skinny moths started to get consistent performance.

One of the quotes I liked is that they were a design breakthrough “but nobody remembers them fondly. Unlike the more moderate scows and skiffs that preceded them.

But look at what was happening to Moth performance. They started having 11ft boat performance, but by mid 80’s the best skiff and scow moths were as fast as the International Contender around a racecourse. The contender has 120 sq ft of sail (moth 85) and is 16ft long (11ft).

Graph of Moth yardstick handicap PYF over time compared to tornado FD 505

Yes … little moths were exceeding the performance of the contender below by the early 80s, proven again and again in first class regattas, Champions against Champions. And the moths with much more left in the tank by pursuing lightness and simplicity ..

With the Wombat design (Oz) and other UK Designs – Moth able to win in most conditions. Sub 40lbs plywood vs 183lbs Contender above. Writing is on the wall.

Moths faster than contenders .. mid 1980s

Nosediving problems solved with … rudder T-foils

One of the problems with skinny moths … actually all moths to some extent … was nosediving. The scow moths solved it in the early ’80s by pulling in some of the lines at the stern to remove volume. For decades they had been trying to fix nosediving with bow modification, almost entirely fruitlessly. It turned out the solution was at the other end of the boat.

The lesson for multihulls is similar, but more about rocker distribution.

A lesson that yacht designers, who are stuck designing boats that look like 1970s dinghy designs may have to learn.

With a skinny moth there’s no volume at the back of the boat to remove, though some tried it with pointed sterns or heavily veed transoms, but with little success apart from making a twitchy boat even more twitchy.

The solution came in the form of the T-foil rudder. No centreboard foil yet.

rudder t foil on moth to stop nosediving

True foiling … the tricycle foiling moth.

Around 2000 .. yes – almost 20 years ago – Brett Burville from Western Australia entered the Moth worlds with a trifoiler.

He didn’t win, but blew the fleet away with performance on some legs. Suddenly foilers looked like a viable course of development.

Trifoiler and why Bifoilers are better – take away lesson for analysing other foilers

So while the trifoiler was taken to be an exciting breakthrough there were criticisms.

Moth sailors pride themselves on being extremely skilful and knowledgeable sailors … and the trifoiler was too easy to sail.

It had self levelling ride

It was boring. Also complicated and expensive. When it came off the foils it was hard to get back on.

Ban foilers … No! Bifoilers are the answer

So the Moths were ready to BAN foiling because the trifoiler didn’t  match their ethos.

The  end solution was to prevent the mounting of foils from the wings, effectively ending the possibility of a trifoil setup.

There was talk of a bifoiler .. or  bicycle setup with a lifting foil on the centreboard and foil on the rudder.

Near Consensus is that the Bicycle version would just fall over.

But some proved out the concept and rather famously sailed up and down in front of the clubhouse.

Here is Ian Ward on what happened

One aspect I think you should add, is that when the Moth association changed the rules to ban foils from the wings, this effectively meant centreline foils were the only practical option for skiff Moths.

The rule makers already knew by this time that centreline foiling was possible.



Ward, Wardy, (remember this name) was pivotal in sharing information and organising for building groups for each new Moth generation to form and work on new developments over the winter season. The groups were loose knit, sharing major developments, but each builder would chase their own ideas with construction and design variations.

That’s the reason for the progression. That and testing of concepts every weekend.

Overview on Control Systems (information from Ian Ward)

Ian Ward wrote:

In response to the rule changes forcing the direction toward bifoilers Brett Burville of Windrush in Perth put twin foils like a biplane on his centreboard. It lifted well but had poor height control. It was John Ilett who saw this and came up with the bow wand controlling the flap on the main foil and developed the foiling system currently used on foiling Moths.

how moths are real foilers and the America's cup cats are fakes.

In effect John adapted the control system used on the Rave foiling trimaran developed by Sam Bradfield and put it on centreline foils forced by the Moth rule changes, using the twist grip tiller trim adjustment developed by Brett Burville for his original Vee foiler.

The  wand system was around well before the Rave foiling trimaran, but it was a successful implementation.

The development did not end there. Initially John used a long version of the standard 300mm chord centreboard. He found the boat was difficult to foil upwind, so he reduced the chord to 120mm which made all the difference. He also added the long gantry aft to improve pitch stability. All of these developments took place over a period 3 months or so with his brother Garth as test pilot.

how moths are real foilers and the America's cup cats are fakes.

Since then, there have been many small refinements, but the foiling control system used on Moths today is completely due to John Ilett.
Rohan Veal bought one of John’s boats, sailed it hard and promoted foiling.
Andrew McDougall copied John’s boat and has steadily refined it further.

240 Moths at the latest worlds is definitely unprecedented in Moth history. It is all due to the addition of foils and the contributions of very many people along the way.

Details of Moth Control Systems to fly in the lightest and strongest winds

When I was watching the first bifoilers race in Sydney it  was like a replay of the extreme narrow moths about a decade earlier.

The regular boats would be ahead, then the foiler would get everything right and suddenly be a leg ahead.

It  took a few years  for consistent enough performance to win a worlds. First the bifoilers would win a race or two, then three and finally when more bugs had been worked out the bifoilers had clear dominance.

Part of the reason for the improvement was sailing technique – world champ Rohan Veal spent huge hours of practice time working out  what  was faster. Rohan worked out that heeling to windward was faster, because leeway would be countered by the tilt of the normally horizontal main lifting foil. This  works because the vertical foil becomes unloaded and the flow patterns where the horizontal foil and vertical foil meet (interference) are much simplified for  less drag.

How to build very light plywood sailing dinghies - Moths and Light Plywood Structures

But lets look at the control systems.

The moth has an automatic and a manual system.

The main centreboard foil is automatically controlled by a flap on the back of the horizontal foil. This photo is of the foils of a moth that hit 35.9 knots.

The bigger foil left with the flap is for the centreboard. The smaller one is the rudder. The bulb at the juncture is a way of reducing the interference between the flow around the vertical and horizontal parts of the foils.

Always remember that a  lot of this  tech was first achieved with timber, epoxy and glass and just a bit of carbon fibre.

The full high tech thing aids production, but much of  the development was in simple materials working at a garage level.

With the original wooden foils the foil was made, flap cut, then the flap was glued on with a gasket of sikaflex or other flexible sealant. Another  method was to make  of glass covered timber and cut through everything except the top layer of glass, so the  glass sheathing acted as a hinge

The main lifting foil on the centreboard is automatically controlled for ride height by the “wand” on the bow of the moth.

moth wand controls ride height

When the wand is out of the water the main foil is too close to the surface … as in the photo above. The wand swings forward under bungee pressure and the flap on the main foil is deflected down to reduce lift.

When ride height is  too low the water hitting the wand deflects it  back overcoming the bungee tension and forcing the flap down. Which increases lift and raises the boat higher.

The linkage for the foil is a rod running through the back edge of the vertical foil that pushes and pulls the flap up and down. The control system between wand and the flap actuator rod is also rod in stainless steel or carbon set in low friction bearings.

Here is a video filmed “under the boat” with the main foil flap in front of the camera lens. The wand at the bow of the boat is being moved showing how it automatically alters the flap for ride height.

The rudder control system was similar originally but manual and controlled by a twist of the tiller extension in the skipper’s hand.

But instead of complicated linkages and a flap hinge it was worked out that the angle could be changed much more easily just by jacking one of the rudder attachment fittings on the back of the boat in and out … and that changes the angle of the horizontal rudder foil.

Cleaner and simpler.

Main lifting foil and rudder lifting foil working together

This brings in a really important concept.

For liftout the boat is low which pushes the wand back to put maximum droop on the main foil flap. Plus the skipper will twist the tiller extension to get the bow up to further increase main foil lift.

For  total control the angles of main and rudder foil have to be independent.

This is critically important to help analyse who is really foiling and who is not.

Once the boat is at the right height you don’t want to keep lifting or the foils will come out of the surface with dramatic cessation of lift.

If the boat is too high the wand goes forward making the main foil flap go up reducing the lift AND ALSO REDUCING DRAG. And the manual rudder foil is adjusted  by the helmsman to keep the bow low. The minimum drag pose.

Why are catamarans messing around with much less effective foiling systems?

There are big debates in multihull circles. The Moth, a little 11ft boat with a small sail is faster than just about all the normal racing catamaran classes.

Cats and tris are used to being the fastest boats on the block.

Not any more.

However they have been resistant to going full foils.

The premier “normal” racing class the A-Class set up restrictions to try and make sure the boats couldn’t foil. No control over rudder or centreboard foil angle while sailing. It was hoped that this would eliminate foiling.

But it didn’t as despite sailing characteristics that include bunny hops and weird attitudes it has been shown that upwind the foils have no consistent advantage, but if everything goes well downwind then there is a distinct, though so far not great, advantage.

You only need a two minutes to have a comfortable margin in a race.


The main foils are set up to reduce lift as they raise higher.

But because there’s no control over the foil angle independently the sailors have to control the lift with body weight. Move further back to lift and further forward to trim for speed.

In stronger winds this can mean really small distances between too far forward and too far back, resulting in all sorts of strange jumping behaviour. By accident and on purpose.

One of the problems is at the same boat angle to the water at 8 knots you have double the lift at 11 knots which means the boats angle with the water needs to be reduced … FAAAAST.

You can see some of the bunny hops and other misadventures in the new Olympic catamaran class the Nacra 17 which has curved foils to help lift the boat. And no control surfaces. This video will show some of the behaviour.

Why the America’s Cup Boats will never be state of the art foilers

Reason 1 why America’s Cup foilers will not be state of the art. – In the America’s cup the same conundrum as the smaller Cat classes.

The original AC72 rules were set up so the rudder lifting foil angle could not be  moved while sailing to prevent foiling.

So instead of having a light simple rudder hydrofoil angle control like the Moth Twist Grip the AC72s keep the rudder fixed but use massive computer controlled hydraulic rams to push the highly loaded centreboard angle.

AC72 limited foiling capability.

Rather famously by 2013 the Kiwis worked out how to foil and were up needing only a single win and Oracle needing to win 8 races.

There are tons involved in moving the centreboard and that is why the team has to keep pumping those handles so crazy during the races. If a rudder flap was allowed it would almost  be in Moth twist grip territory. Could be so simple.

It’s classic sledghammer to crack a walnut territory.

Oracle went on to win the races it needed straight through with an all time turnaround of boat speed and handling.

The sudden improvement of Oracle’s fortunes were purely because of a new hydraulic control system to allow finer control of the centreboard angle. Suddenly they had the edge and the crew exploited it to the max.

Reason 2 why America’s cup foilers will never be state of the art

We saw that the progression of the Moths moved from them taking off in 8 knots  of breeze, then 6 then finally after more years of development they can now take off in 4 knots of breeze.

If the moth gets  up it  can sustain flight in winds as low as 2 knots. Most amateur sailors would think there was no wind but  the moths  can fly.

If you want to race every Saturday and Sunday … this is necessary.

The America’s cup boats on the other hand have a minimum wind limit for racing of 10 knots of breeze. In ten knots the Moths will be flying happily at well over 10 knots upwind and getting up towards 20 downwind. This is really fast.

Here is a moth in what looks like 5 to 7 knots of breeze.

However the 2013 and 2017 version of the AC boats were not required to race in light winds. This kills the potential for finding full range performance like the moths

Further the AC72s in 2013 had an upper wind level of 20 knots.

Here are a bunch of kids sailing their 8ft boats in winds well over 20 knots.

Happily the maximum wind strength was increased to 25 knots for the 2017 America’s cup racing. But the lower limit remained at 10 knots because they are afraid the boats will look boring.

But this is where discovering full range performance lies.

What does foiling fakery look like

1/ Selection of windspeed

We have seen that full range performance comes from regular racing with no lower wind range. The boats have to fly around the racecourse in the normal club racing range of minimal wind through to about 25 knots.

If a type of “advanced foiling” boat or event doesn’t race in under 10 knots of wind, then it doesn’t have full range performance.

It is reasonable to have a lower limit for events of 8 knots (as an example) but the lower wind speed range should be reduced by 2 knots every successive year.

The boats will just have to find the performance.

2/ Cherrypicking video footage

This was a big problem in the early days, but still continues as a problem.

The Moths do not need to select footage to look good. Whatever the wind is doing, whatever part of the racecourse they will look great.

I’ve seen a bunch of cat foiling footage that showed foilers losing so much height to non foiling boats of the same type it was laughable as they foot off to try and get up. Whereas the conventional boats just fly away fully powered up.

Notable Foiler 1 Quant 23

Quant Boats

I was very sceptical that the Quant made sense. A keelboat with foils seems counter intuitive. Ditch the keel weight and go faster.

quant 23 foiler

I accused Michael Aeppli, the developer of using selective footage to bolster his claims.

I was turned around completely. Ian Ward, the chap probably more responsible for the bifoiler concept for the Moth had been sailing the Quant 23 in Switzerland.  This is some of what Ian Ward wrote to me.

It shows a wide range of acceptable windspeed, and harking back to the trifoiler “being too stable” for the Moth guys … the  Quant turns that stability into a virtue. With no moving parts.

Since then more and more footage has come out of the Quant with some really significant speed in very light winds. Strong wind speed is a given. Light winds are the performance frontier (as I keep saying, they are the measure of efficiency).

Ian Ward: “I have followed your designs and love the Goat Island Skiff.
I see that you are also following the Quant 23 scow development and probably also realise there is a breakthrough happening here. I really think that Michel Aeppli (Michi) and Hugh Welbourn are on to something.”

“At first I thought the concept of lateral foils may help a little with stability, but I was really quite impressed with Michi’s idea to use them to lift the boat entirely free from the water. This provides huge righting moment without the need for wings or trapeze. It is even more surprising that the ride is stable and that the boat can plane on the foil. There are no moving parts, Hugh Welbourn has done a good job with this. I think the latest photo of the white Quant 23 says it all. He is lifting out in 4kts windspeed and sits on 12-13kts boatspeed.

I know of no other boat, let alone a keel boat which can achieve this. It also highlights what a huge advantage foils really offer, even in light air if it is done properly. Top speed is typically 23-25 kts for the Q23, which is more than enough for an average sailor!!

While the lateral foils cannot provide righting moment unless you have some forward boat speed, they do nevertheless contribute to roll stability, making the boat quite forgiving and easy to handle. If you increase the rig size, this may be an issue, but I do not think it is a big problem.

Glide Free Laser foiling kit

foiling for everyone

Glide Free is another Ian Ward project. An attempt to “democratise” foiling.

It plugs into any Laser Dinghy. It has also been fitted to the Optimist and O’pen Bic dinghies.

You can see the wand trailing the centreboard foil in this video.

It integrates the ride height sensor with the main lifting foil. It is all aluminium extrusions.

Some things are counter intuitive.

The full laser rig is slower than the smaller Laser Radial rig. The thing is that with foils instead of the Laser sailing at 4 knots into a ten knot wind, it will be sailing much closer to 10 knots. The apparent wind (the wind the sailor and sail “feel”) is roughly 14 knots for the non foiler, but 20 knots for the foiling version.

14knots of apparent wind the Laser is really nicely powered up. But in 20 apparent a lot of sail has to be allowed to shake to depower which increases drag.

To be more precise the feeling of wind strength is doubled … which means that smaller sails work well.


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One thought on “Foiling – Forefront vs Fakes

  1. More From Ian Ward:


    Agree that it is really a step by step development, many people go unrecognised and unfortunately lots of good stuff gets lost along the way. What you say about the sea hugging skiffs Moths is all true. The high wings, narrow hull, pintail stern, flat run, Tee foil on the rudder are all specialised design features which contributed to a very fast boat which planed easily, did not nosedive or pitch in a chop. Most of these features are embodied in Moth today but are no longer relevant once the boats left the water on foils!

    The same applies to the evolution of Scow Moths, flat planing sections, narrow sterns to prevent nosediving, curve in the side for displacement performance when heeled and the wings provide enough power to plane upwind. I also sailed NS14’s which went through their own intense development with fine bows and flat planing surfaces aft.

    It is such a pity that most of these lessons seem to be lost or ignored. A whole new generation of dinghies are now being released such as the RS Aero, Melges 14, Devoti Zero which use carbon for spars and yet otherwise they are simply old displacement designs, wide transoms which promote nose diving, soft full sails, no flat fast planing surfaces, fat hulls with full bows, and above all they have narrow overall beam, so they have insufficient power to plane upwind.. It all seems such a waste when they could be so much better!

    Another pet hobby horse is the use of solid wing rigs on the big AC cats. Sure they are impressive, but so impractical. What I would really like to know is if these rigs are actually any good compared with conventional state of the art Moth, sailboard and Cat rigs. In both A-cat and Moth classes the solid wings have proven slower, especially in light air. It is such a pity that the AC rules do not allow any real development or comparisons so we could learn something new and useful to other classes.

    Feel free to add these comments and those about John Ilett as I really feel he deserves recognition for his efforts.

    So many people now somehow think that Rohan Veal or perhaps Andrew McDougall developed the foiling Moth, when it was in fact a process with many people involved over a long period of time, well before either of these guys made their own important contribution.

    all the best, Ian

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