Moth on Foils: 35.9 knots(41.29 mph)

Moth on Foils!

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Foiling kiteboards have proven beyond a shadow of a doubt that jumping and re-entering can be done routinely. The video clearly shows the Moth jump the wake and, as it does, the wand springs forward so that when the foil re-enters the water the flap is max up: that caused the crash-no ifs ands or buts. There is no way a Moth will recover from a jump with the flap up when the foil re-enters-not a chance in hell.
As to manual control being a solution: it is one of several. Manual foil control has been proven to work on the Rave foiler, AC 72 , my 16' foiler, kite foilers, foiling windsurfers among others.

see wake jump and resulting crash about 1:31 in:

https://www.youtube.com/watch?v=xHkPfnhLoZY

 

The comments are partly correct. By the time Rasher is airborne the main foil is that close to the surface that it is of little help irrespective of the flap position and unless its angle of attack is reduced it will probably stall on re-entry. A a major contributor to the crash is that the rudder foil continues to hold the stern up and in combination of the bow down pitching moment of the sail the boat goes seriously bow down. Manual control of the rudder foil could minimize or avoid the crash if full trailing edge up were applied early when the increase in boat height caused by the wave commences.
The reason the kite foiler survives this condition is the the kiter can readily stop the bow down motion.

 

Nobody is disputing that but a moth is not a kiteboard. Have you noticed the very different foil planform (ie low aspect shapes) adopted for foils intended for jumping and wondered why those shapes might be used? User-friendly performance when stalled is a priority for those types of foils. It isn't a priority for moths who just seek to avoid the ventilated or stalled states completely. As noted above, kiteboarders also have options to re-balance the loading between fore and aft foils which helps achieve the recovery.

The flap position is largely irrelevant in circumstances where the foil has ventilated and re-entered the water in a stalled state. In fact, if the flap were set to stay down it might exaggerate the boats cartwheel as it trips over the stalled foil.

 

Moth on Foils!

The foil entering the water flap up caused the crash. Had the flap been down(or maybe neutral) the boat wouldn't have crashed.
PS- there are numerous shots of Moths crashing immediately after the wand springs forward in rough water-it happens so often that it is typical of the Moth foil system. The rough water video's of the Sorrento worlds are posted here.

 

But the kite also has many more degrees of movement of the main foil. Doesn't that mean that the fact that a kite foiler can survive this condition is no indication that a boat with a controlled flap of any sort can survive?

By the way, Doug, can you provide us with a video or independent evidence of your 16' foiler surviving a wave crash at that sort of speed?

 

It seems we are going backwards. At least in 2007 you could acknowledge the low aspect (delta) foil planform as a key difference.

http://www.boatdesign.net/forums/archive/t-17190.html

 

Moth on Foils!

After watching the video some more it suddenly dawned on me that if the Moth had had a midship wand( like Bradfields system)-it would have moved the flap down before the main foil re-entered and more than likely avoided the crash.
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As to manual control: it's been proven on numerous boats and in the Rave class was proven to be faster than wand equipped boats. Rave manual control involved not just mainfoil lift and rudder pitch trim but included a third control for differential foil lift-RM. So to say it can't be done on a Moth is nonsense.
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CT- 1) No! 2) my 16' foiler never crashed.
M- there is little doubt that lower aspect foils are better for jumping-that doesn't mean that a Moth foil won't re-enter successfully-but it has to be controlled manually or have a mid-ship wand to do that repeatably.

 

I think it's pretty remarkable how well the boat (& skipper) managed the situation. You may call it a crash, because the boat came off its foils, but it stayed more-or-less upright - neither capsizing nor pitch-poling (unless there's more that the video doesn't show).

 

Never crashed? So you achieved in a short period of sailing one boat what the combined efforts of Wardii, AMAC, Brett Burvill, the Illets, Andy P, Rohan Veal, Adam May, Nathan Outteridge, Maconaghys and Peter Burling have not achieved in more than a decade of brilliant sailors and designers working with hundreds of boats?

Well, I AM impressed. Of course, since you have been telling world class Mothies you know more about what they should do than they do for years, it's not surprising that you are still doing so.

How often did your boat sail at that speed, in those conditions, over that sort of wake? Was it really as fast as the latest Moths, which is that it would have to be to make it really comparable? Why did you give it up when it was actually well ahead of contemporary Moths?

 

My foiler was only sailed in relatively light air and small intercoastal waves. It used a manual control system that worked-but not perfectly.The hull was the biggest problem in short intercoastal chop causing the boat to takeoff later than it would have with the right bow. And it probably wasn't as fast as a Moth but since there were none around I can't say for sure. I ran out of money to develop the boat further and I had physical problems that made working on the thing very difficult. But, the manual foil system worked well and the boat was easy and fun to sail for the most part until a component bent that made it a bit difficult. The principle worked and it simply needed refinement. From my experience testing the boat I'd say that if it had run into a wake like the Moth did in the video it would have crossed with no drama. The manual system, when it was working right, was just plain fun.
The boat inspired the Fire Arrow and the hull*, foils,sails and rig are still around and may be used again on the Fire Arrow proto if it ever gets built.
*my sailmaker has the hull

 

Moth on Foils!

Classic Moth on foils: https://www.youtube.com/watch?v=A9urDKT88LU

 

No, it didn't. The foil ventilated, the boat dropped and hit the water before flow could reattach and create enough lift to stop the drop. The flap was irrelevant.

The flap position was irrelevant once the foil ventilated.

The wand going fully forward is not the cause of any of the crashes you've seen. None. Those crashes are caused by the foil ventilating as it comes out of the water (typically exiting the front of a wave). Moths often sail with the wand fully forward in rough water, they don't crash because of it.

 

It would not have avoided the crash. The wand had already moved the flap fully up well before the crash, but the boat kept rising due to increased apparent AoA as the foil move through the front of the wave. Reduced lift from the raised flap was insufficient to lower the ride heigh fast enough.

Moth main foils do not develop downforce with the flap fully up. They just produce less lift. At full speed downwind, somewhere above 20kn, they are sailing with the flap partially up.

Things that may have avoided the event by stopping the foil from ventilating:

1. Set for a lower ride height
2. Heal and steer to windward to drive the bow down
3. Bear away and steer along the wave until the flap starts to lower the ride height before exiting the wave (less effective than coming up)

This particular case is unusual as the wave isn't aligned with the wind, so likely caught Chris out. He was also riding very high in flat water, so it didn't take much to induce ventilation.

Because you did extensive testing with otherwise identical boats?

Moth crew already constantly manually adjust sheet and tiller, one in each hand. They also have rudder AoA, ride height, gearing, wand length, wand return tension and stopper tension (in addition to vang, cunningham, outhaul, forestay tension and rig cant). Sure, add manual control of the flap. No reason it can't be done other than humans only have two hands and foot controls on small, high performance dinghies aren't popular.

Might be something to do with feet being fully employed keeping the crew aboard using the toe straps.

Ventilation crashes are certainly survivable (i.e. not result in a capsize), but not when going ten tenths in a race. The idea that a Moth can recover from a main foil ventilation and continue foiling without the hull at least hitting the water and returning to displacement mode in all but the most exceptional circumstances (of which I can't conceive) is fantasy.

The theory behind Chris's bowsprit is that it moves the wand further forward, increasing separation between the wand and flap, giving more time for response. You're saying that a guy who is arguably one of the top 10 Mothies in the world (a group that includes some extremely talented sailors with multiple World championships in multiple classes) has it wrong? That he should be moving the wand back near the main strut?

Yeah, right.

 

Moth on Foils!

To say the flap has no effect is nonsense. There are dozens of shots particularly in the Sorrento videos of crashes as a direct result of the wand springing forward, raising the flap max up--without the foil exiting the water.
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The thing about the forward wand is that it allows a coupling between pitch and ride height control. Whereas on the midship wand the wand enters the water in line with the F&A CG of the boat so the wand controls only ride height with no extraneous "signals" due to the boat pitching. You can watch many videos of the Rave foiling and never see a crash like the Moth.
This "time for response" argument is just wrong-all you have to do is calculate the speed of the boat and of the waves to see that at any boat speed above about 10 knots the wave that moves the wand is long gone by the time the flap moves. I can see the forward wand working just as well as a midship wand in docile conditions but when it's really rough-crash after crash.
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There were two guys that outfitted their Raves with manual control and in addition to extensive two boat testing they raced and won a lot. They were faster than wand equipped Raves.
It's just common sense: if you eliminate the constant flap movement caused by a wand, drag will be reduced.
I'm amazed that no one, to my knowledge, has done a manual system for controlling the Moth main foil-designed right and learned after lots of practice it would be faster. And it would eliminate all the wand controls completely.

"....ride height, gearing, wand length, wand return tension and stopper tension...."

 

You are seeing what you want to see. The foil ventilates before it becomes airborne, watch for spray from the bottom of the strut. The main foil never, ever cause such crashes (unless it breaks, but that's not the topic here).

See if you can find a single foiling Moth sailor who agrees with your opinion. You will not find one.

Here is a video of a Moth sailing for quite some time with the wand fully forward and well clear of the surface. There is an extremely short ventilation (indicated by spray from the strut) that causes it to come back down. Likely the hull hit the water but the video is cut before then.

McDougall+McConaghy 2015 Moth Worlds - Day 4 2:22

Here's another of a full–on crash from ventilation. You can see the wand is fully forward for quite some time, but the boat keeps rising. No down force, no crash from the flap, it keeps going until it ventilates (lots of spray from the strut). You might also note that once it goes bow–down, there is no change in attitude, the flap has zero effect. The boat just goes down the mine.

Moths Crashing in Super Slow Motion 1:46

There are many other videos, but these are exemplar.

I've been sailing a foiler for about 6 years now and in rough conditions frequently sail for 2 or 3 seconds on the crest of large waves with the wand way in the air, waiting for the flap to bring the boat down. If it doesn't, a bit more windward heal and a flick of the tiller to point higher uses the main strut to push it down. A bit of a risk though as it means increasing speed and I have to bear away again sometime. If I crash, it's because the foil ventilates, not because of the flap.

Presumably you mean the tri–foiler. It is a completely different boat and there are nowhere near as many videos of it sailing as there are of Moths. Even of the small number that are available, there are some pretty good crashes. To say that it's lack of crashes is due to the position of the wand with respect to the foil is complete nonsense.

Pitching of the boat does not affect the wand/flap response to any noticeable degree. When you see Moths pitch up coming out of a wave it's from the increased apparent AoA on the foil in the front of the wave, the flap can't reduce lift enough make the boat go down to the trough (and it absolutely never, ever creates down force). The rudder is used to trim for pitch to reduce main foil AoA. It has other effects too, it can be used to promote foiling in light air, and to give a bit of bow–up on rough down–winds to stop burying into the back of waves.

Do you think that in about 12 years of development, foiling Moths haven't tried wands near the strut? Of course they have. And why are people moving them as far forward as they can?

And I'm not talking about backyard wannabes, I'm talking about some of the very best sailors in the world. So it's your intuition vs real sailors in the real world with years of actual experience.

Ventilation crashes are a feature of downwind sailing, not upwind. In say 15kn of breeze (which is about where the chop starts to be big enough to worry about) the waves are doing about half wind speed, or say 3.5m/s. The boat is doing about 20kn or 10m/s, but at 45° to the waves so about 5m/s in the direction of the waves. The resulting differential is about 1.5m/s with respect to the waves. So the wave crests take about 1 second between wand and strut, plenty of time for a response. Even more time if the boat heads up a bit to run along the wave.

I've been doing this for years, actually on the water sailing mostly in a shallow bay with a serious short chop but also in open ocean swell and lakes of various sizes. The theory is the same in every case, just the waves are different.

Funny how in over a decade of development by world class sailors, designers and builders no one has thought to put a manual control on the main flap (I'll bet someone did try it, but it wasn't very successful). Even double handed foilers don't have manual control of the flap, and they have a spare set of hands. So while one aspect (less flap movement) is the only common sense you consider, the many other variables that would make it slower (if not impossible) is the common sense that also occurs to everyone else.

Why do you think a person, over a couple of hours of sailing, wouldn't make a mistake through misjudgement or tiredness, even though they are constantly trimming 3 controls with only two hands? And how would such a boat tack? Foiling gybes aren't easy, and foiling tacks are a serious challenge. Expecting the crew to also manually adjust the flap at the same time for maybe 50 tacks and gybes as well as all the sailing in between without error is absurd.

You have never sailed a Moth, have likely never been to a Moth regatta nor spent time talking to Moth sailors. If you did, you wouldn't have such ill–informed opinions about them.