High Performance MPX Foil/Self-righting Trimaran-The Test Model

WOLF---daughter of fire arrow

I've done some design work on the boat:

1-Total buoyancy of ama hull + "curved piece"+ 3"(76.2mm) diameter cross arm tubes=335 lb(152.3kg). Total boat plus crew weight, about 400lb(181.82kg).
a- ama hull=2.54 cu.ft.(.072 cm)=162.6lb( 73.91kg) buoyancy
b- ama "curved piece"=2.1 cu.ft(.06cm)=134.4 lb(61.1kg)
c-Total-ama hull +curved piece=297lb(135kg)
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2- Static RM with curved piece and ama hull(but not cross arms) immersed:
2227.5ft.lb.(307.9kg/m). Equivalent to 1.24lb/sq.ft.(6.054 kg/sqm) pressure on the rig.

ok, Peter?

 

WOLF---daughter of fire arrow

The ama, curved piece and ama UptiP foil will look very much like the Fire Arrow and work exactly the same way.
--The planing surface area may be adjustable though the purpose of this planing ama is not to lift the boat but to have minimum drag when the ama makes incidental contact with the surface at speed.
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The ama foil may be a slightly different design without the reverse curve on the uptip portion of the foil. If that is done it will be because, while this configuration helps generate max lift when the foil is underwater, when the tip breaches the surface it does so at a shallower angle causing more drag than it would otherwise. However, the test foil has spent most of the time underwater and not breaching the surface.


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Fire Arrow planing ama: (STB UptiP foil still has iFlap-removed from port ama foil)



Fire Arrow showing mostly unloaded port ama foil. Part of the drag in this configuration is due to the shallow angle of the reverse curve portion of the foil:

 

Peter,
it sounds like you are downplaying the value of a ((dh/dt)+h) input vs just h. That's bad engineering.

There are other ways of getting control but they bring costs and limits. Specifically, frequency response, and recovery time.

 

Midship Wands

The facts,as I see them now, are that there is ZERO problem with midship wands on the vast majority of boats that are using them or have used them: Osprey, Rave, Skat, F3, Fire Arrow, Whisper and the F101. I'm very leery of trying to fix a problem that, by all accounts, has no symptoms and has never been reported by anyone using the boats I listed.
However, elements of the Moth class say that midship wands were tested and that the bowsprit wand works much better. Ok, for the Moth.........

From "Moth on Foils!" about 8 years ago:

The midship planing wand was invented by Dr. Sam Bradfield and used on numerous multifoilers including the Rave and SKAT(and Osprey- now the Whisper cat and F101 trimaran-dl).
And now it turns out that at least the midship part has been adopted experimentally by Jean Pierre Ziegart who sailed to a 14th out of 36 boats in the Velocitec
Speed Challenge and to 31st out of about 95 boats at the UK Moth Worlds. He also used dual wands first pioneered by Thomas Jundt on the 26' bi-foiler Mirabaud. A midship wand also is used on the Foiling 18 "Access". Very interesting-




This is the only Moth I've ever seen with midship wands. Jean-Paul Ziegart's Moth:

picture by Thierry Martinez-

 

How many of the boats with midship wands have been raced in fleets of 50+ in all conditions? Many configurations look good in flattish water and moderate conditions, or when eased back.

 

Midship Wands

Midship wands have been tested for thousands of hours in all conditions.

 

There is actually a scientific mathematical proof of stability -a system can be characterized and graded over different conditions. The prerequisites for a typical control theory class are math through calculus covering differential equations. If you have someone help you, there are ways to do simple math models in a spreadsheet or any programming language.

My point is you don't know if any of those boats have a problem, or what conditions they can handle. I also think that since you don't know and you are following, Tom Speer is the best when it comes to explaining and guidance.

There is another engineering practice called "Design Failure Mode Effects Analysis" DFMEA that might be useful. Because your MPX has so many foils (redundancy) it doesn't matter much if the T-foil under the main breaches or ventilates. The result is just a mild increase in drag. Bi-foilers like the moth have much more severe consequences.

 

Fire Arrow Foiling System Testing and Development / WANDS

Thanks, Skyak. My problem with the midship wand vs the bowsprit wand is that I spent a lot of time talking to Dr. Sam about this very subject. There weren't any bowsprit wands on Moths back then but several of the early foilers used bow mounted wands that Dr. Sam thought weren't as good as his midship wand.
I'm being told by people I respect that the bowsprit wand greatly improves pitch stability when Dr. Sam said such a wand would tend to have pitch coupling with altitude(which Steve Clark says is good) and Dr. Sam said was bad. He said that pitch was controlled by the rudder T foil and altitude by the midship wand. Yet Dave Clark is saying that pitch control is really a function of the bowsprit wand. But Ron Price designer of the Whisper Cat and F101 trimaran -both with midship wands-says that pitch coupling can be bad and the midship wand takes care of it.
If it hadn't been for my long conversations with Dr. Sam about this I might be more easily converted. But I have a lot of time on full size and RC foilers with midship wands and never a problem.

 

Seasons Greetings/ Merry Christmas!

For those of us about to celebrate Christmas, here is a unique card by Cape Horn Engineering that fits right in this thread:

 

The T. Speer quote above says it all. I can't make it any clearer other than to do some math to show you the conditions where the bow wand input is better than midship. "Coupling" inputs is not a good thing generally, but in this case pitch input is important and it will simply be added to height anyway. I am at a loss to think of any benefit to going without pitch input -lift is proportional to alpha.

So midship wand is inferior, is it "good enough?"
-porpoising (fundamental instability, even in flat water) -can be dampened out by other means -example; a spring in series with the linkage and a damper on the flap. This slows the natural frequency of the system. Reducing the 'gain' will also reduce instability. Note that both of these 'fixes' can lead to problems in more challenging conditions by slowing the response. Pitch input 'dampens' the output without slowing the response.

If you think about it, all the wandless designs are midship input. They get by with well chosen gain, natural damping, and crew input and balancing. As an engineer it is kind of insulting that such expensive boats crash or are unsafe in relatively common conditions -for lack of very basic engineering.

 

Fire Arrow Foiling System Testing and Development

Thanks, Skyak....

 

Fire Arrow Foiling System Testing and Development

This is the current Fire Arrow Dual Wand set-up. Dual wands are used because the boat sails at an angle of heel. They could be eliminated by using a variation on the Whisper wand set-up.

Picture shows the Fire Arrow dual wand mount. The plate also supports the daggerboard and can slide fore and aft a small amount:

A- Attachment point of the 4/40 threaded rod from the daggerboard.
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B- Attachment point of the pushrod from the mainfoil flap.
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C- Former attachment point of the "spring" line used to hold the wand against the water. It is now attached directly to the starboard wand.
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D- Dual wand axle.

 

Doug. I'm sure you will be pleased to know, one of the big monohulls sailing in the annual Sydney-Hobart ocean race, on Boxing day, has lifting foils.

 

Foil Assist

Thanks, Paddy! I imagine you're referring to CQS with DSS. Their foils have flaps for the first time on a DSS foil. Can't wait to see how they'll do.
Wild Oats had DSS for a couple years...
Merry Christmas!

 

Wand theory

Two recent quotes from Tom Speer on Wands for foiler control:

1

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2