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

Fire Arrow Foiling System Testing and Development

Fire Arrow Foil System Advantages(also see post 2297)--

One of the great advantages of using a properly designed UptiP foil on a foiling trimaran ama is SIMPLICITY: on the Fire Arrow the ama foil has NEVER needed to have the angle of incidence adjusted while sailing as is common on many UptiP foil applications. And if the foil is properly designed for it's application ,it's efficiency will be apparent. As shown in the pictures below the lee ama flies before the main hull, but as soon as the boat speeds up and the main hull flies the lee ama altitude remains the same. That illustrates that the lee UptiP foil is working PERFECTLY in two different load and speed cases.See pix "A" and "B" below.
The Fire Arrow uses a wand controlled main foil which controls the altitude of the main hull and the angle of heel of the whole boat. Further, and this is very important: the wand controlled main foil works with the single rudder T-foil in a bi-foiler arrangement and the two together control the ride angle of the lee ama UptiP foil. That prevents pitch excursions caused solely by the lee ama foil.
The way the mainfoil works is that as soon as the main hull flies the mainfoil begins to unload with the lee ama foil gradually taking the majority of load. That allows the mainfoil to work with the rudder T -foil to control the pitch of the boat with far more pitch authority than on a conventional tri. And, using a wand controlled(or similar) foil on the daggerboard allows the main hull to fly MUCH SOONER than it would if it had to wait for wind pressure to do it.
The mainfoil can also develop substantial downforce* increasing the righting moment in response to gusts. All this is done 100% automatically making for a simple, robust system that requires ZERO crew attention!
* with downforce, the main foil works similarly to a Moth foil with Veal Heel, generating a component of lift to windward.See illustration below.
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The vertical portion of the ama foil is at +3 degrees AOI. The vertical portion of the daggerboard is at zero degrees. So the UptiP ama foil is developing lift to windward to allow leeway coupling and develop lateral resistance for the boat particularly upwind.
In stronger conditions, when the main foil develops down force( upwind), the leeway components are greater than the vertical portion of the UptiP foil can effectively handle, there is a small extra component of lift to windward(due to downforce)-while the vertical portion of the ama foil is still working at 100%. The daggerboard is designed to be unloaded by the lee ama foil to reduce drag and facilitate leeway coupling.
However, it should be pointed out that the ama foil will still provide substantial vertical lift with little to no leeway coupling-like can occur off the wind. Lift substantially(and automatically) increases upwind because of leeway coupling.
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Testing clearly shows the progression of the boat to full foiling from the problems encountered at the beginning-the last video is 100% proof that the foil system worked perfectly-regardless of any uninformed attempt to say otherwise. But testing is not done yet even though we reached a major milestone with the boat foiling in a 5 mph wind while using two different altitude control systems simultaneously. Hopefully, starting in June we'll get a lot more video and in stronger wind. But July 24th, 2014 was a major accomplishment for the boat after a great deal of development-and we will build on that as testing and evaluation continues.
Attributes of the Fire Arrow foil configuration:
1) allows an oversquare trimaran to foil in very light air,
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2) allows full foiling upwind and downwind completely automatically without any adjustments by the crew,
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3) allows for retractable foils controlled from the cockpit,
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4) allows the lee UptiP ama foil, with an AOI of +3 degrees, to unload the daggerboard(AOI zero degrees) for reduced drag and enhanced leeway coupling.
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5) the foil system has considerably greater pitch authority than any conventional trimaran,
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6) allows automatic control of the angle of heel of the whole boat,
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7) allows automatic control of the ride angle of the lee ama UptiP foil.
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8) allows mainfoil to automatically unload as the mainhull flies ,dramatically reducing drag.
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9) allows automatic gust response with instantaneous increases in righting moment (automatically) as required.
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10) allows a "Two Stage" ama that provides back up buoyancy if needed but allows the part of the ama that would normally make incidental contact with the water, to be as small as practical.
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The short version of the final test video from 2014 showing the boat foiling in very light air(5mph max). The first day that the foil system worked 100%!
The foil system worked perfectly in this test but I still had a problem tacking in the very light air . The waves were bigger than they should have been for the amount of wind and I didn't handle the tack as well as I might have. If you notice when the boat takes off on foils on port tack I decide to tack rather than gybe. I believe that had I gybed she would have continued flying thru the gybe. I'm convinced- in the right conditions- she'll gybe on foils. She already has shown that she will foil upwind,again-in the right conditions.
https://www.youtube.com/watch?v=7Mok3d4KiMI


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The pictures below illustrate that the lee UptiP foil is working PERFECTLY in two different load and speed cases-providing automatic altitude control:

 

WOLF---daughter of fire arrow

WOLF Summary

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WOLF---daughter of fire arrow

Like the Fire Arrow, the full size WOLF will use a wand surface sensor(or sensors) located midship. Midship wands were used on Bradfields Rave(which I have a lot of experience with), Osprey and Skat . I used them on my production F3 RC foiler design as well as on the Fire Arrow Test Model.
They work very well in all conditions and are very simple and easy to work with.
Relatively recently the Whisper cat and F101 trimaran have been introduced with trailing midship wands and the Laser foiling kit uses a similar type of wand. I like these wand systems because they work really well and are extremely simple. The Whisper/ F101 wands are integral to the daggerboard and not attached separately to the boat like the Moth wand or the Fire Arrow dual wands are . Below is a picture of the Whisper daggerboard + foil with the wand hanging vertically along the trailing edge. This allows the board to be simply inserted thru the bottom of the trunk . On the Whisper they have to be removed to trailer the boat but if they were used on the fullsize Fire Arrow and/or WOLF they could remain in place for trailering. If the Whisper type wand was adopted by the WOLF it would save having dual wands and eliminate the cross boat axle and attachments like the Fire Arrow has.

Whisper/ F101 foil with integral trailing wand. Wand is the black thing hanging parallel to the daggerboard trailing edge:




Whisper with trailing midship wands:

 

WOLF---daughter of fire arrow

More work today on the concept model which has changed a lot from the early pictures(see page 162, post 2416). Both amas are made, both curved pieces laid up from carbon(to get the scale radius) and all the "shaping wood" is on the main hull. Float tested the main hull and its right on target.
Considering making the pitch of the ama hull( relative to the curved piece) adjustable*
Everything is still very tentative including whether or not this project can even get done. But its looking good for a fun little flying speedboat.......

*UPDATE: this isn't such a good idea unless I'm willing to increase the range of ama foil rake adjustment.

 

WOLF---daughter of fire arrow

Two pictures of the unfinished parts-not properly oriented with respect to each other--just a rough preview showing the two ama hulls, two curved pieces and the main hull:

 

WOLF---daughter of fire arrow / "Curtain" sail extension

I don't know whether the "A+B" version of the sail extension will work or not. I first thought about it a couple of nights ago. The idea is to come up with a really good(or at least vastly improved) seal of the foot to the boat to reduce drag.
The "A" section is similar to whats being used now and similar to a sail extension I had made for the aeroSKIFF in 2000-2002-don't remember exactly when. I still have it and it was a real pain.
This concept is to have the boom high enough to clear the crews head(on WOLF) when tacking or gybing but have the sail extended to the bottom of the cockpit and aft past the clew. The "A+B" version would have some sort of slit in the middle so the crew could go from side to side.
Lots of problems to iron out but I think it could work primarily because the sail doesn't have to go out very far between upwind and downwind because it is on a foiler. Haven't discussed this with Scott(my sailmaker for 20+ years) but between us I bet we could make it work. And the result would be a very powerful sail.

 

WOLF---daughter of fire arrow

The first priority of this new boat(should it actually get built) is that it starts to foil in a 5 knot wind. Second priority is that it is really, really comfortable. These seats will be very light, adjustable(probably) and have waterproof 3" cushions with relatively high backs.
I've ordered Duratec and filler-the next job-as time permits- is to "cosmetisize" the model and, eventually, get it painted. Need to assemble crossarms and curved pieces to ama and then the whole assembly to the boat on each side.








click on lower images for bigger picture:

 

WOLF---daughter of fire arrow / Two Stage Ama

I assembled the "curved piece" to each ama hull and each assembly is now a Two Stage Ama( stage 1=hull, stage 2=curved piece )-see p160, post 2387. Its important to understand that the boat is not intentionally sailed on these amas-they are designed for the lowest drag incidental contact only, at slow or high speed.
On WOLF, the Two Stage Ama has a total buoyancy in salt water of 252lb.(115kg) Including the crossarm carbon tubes it is 290lb.(132 kg) Estimated total sailing displacement of the whole boat is 400lb.( 182kg).

 

WOLF---daughter of fire arrow

I'm stuck until the middle of next week on doing the finish work on the pieces already built. The company, US Composites in West Palm Beach apparently took off between December 23 and January 3 though nothing stopped them from taking my order and I missed the fine print about their holiday plans. They are the only company I've found ,so far, that carries Duratec in quart cans so thats the way it goes.
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I'd really like to increase overall beam to 17+ feet but the limiting factor is how the amas will fold-the 3" carbon tubes are plenty strong w/o waterstays.
The wider the boat the better the ama foils work and the smaller the "Two Stage Ama" can be-within the limits of the structure and stiffness required for the foils.

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At this point the Wolf main hull will be built of foam and carbon starting with blocks of EPS foam cut as in the picture below, then glued together, shaped and carbonated. The fullsize foam blocks ,cut, is about $250......

click for larger picture:

 

WOLF---daughter of fire arrow---Design

I made a mistake(or two) in laying out the cross arms, mast and daggerboard position.
Looks like I set the daggerboard up relative to the centerline of the forward cross arm rather than to the aft side(+clearance) of the crossarm. That means the daggerboard has to move aft but since I need to maintain a specific distance between the transom* and the quarter chord point of the daggerboard(which I somehow got wrong too), the boat needs to be lengthened. So the overall length has to go to 15.46'(15' 5 1/2"/ 4.71m) from 14.75'(14'9"/4.45m). This set-up allows the mast to be stepped on the centerline of the forward crossbeam and allows the daggerboard to clear the cross when it is raised. If I use a 7.5" wingmast, the mast may have to be rotated when the board is raised. The rig, cockpit, amas, forward and aft cross positions are unaffected. The CG is slightly affected but in a good way so, all in all, problem solved.

*The transom is a convenient point to use to reference this measurement(.54LOA) but what actually counts for the pitch stability of the boat design is the distance between the quarter chord of the rudder hydrofoil and the main (and ama) foil. The "problem" could have been solved by using a sort of mini gantry-similar to but smaller than the one standard on a Moth but I don't like that solution.

 

WOLF---daughter of fire arrow / "Curtain" sail extension

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Scott and I discussed this idea today and he thinks it might be able to work-at least we're going to try-- assuming we get that far. The shape of the sail below the level of a "normal" boom(more or less) is not very important-all it is doing is sealing the high pressure side from the low pressure side.....

 

Wand Surface Sensor on the Whisper System

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An experienced multihull sailor that I respect just told me that one of the problems with the Whisper system is that it has a cylindrical rod right at the trailing edge of the daggerboard and that that would disturb the flow around the board. I had assumed that "people" would understand that that rod(tube) was the surface sensor or wand. It is only in that position when the boat is not moving! At the slightest movement of the boat the wand trails way back causing the flap on the hydrofoil to do down creating vertical lift. It is NEVER in that position when the boat is sailing.
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The reason I'm considering using them is because of their simplicity compared to either a Bradfield or Moth system.

 

WOLF---daughter of fire arrow / Two Stage Ama

The ama on this boat is designed for more or less incidental contact with the water-it is not designed to be sailed "on" since it will be flying from a 5 knot breeze on up.
However, I've been curious about the idea of a planing ama for some time and that is why the bottom widens out as it goes aft. For the "normal"(incidental contact) use of the boat I don't need such a wide planing surface but I want to be able to experiment with it hence the wide bottom. I'll be able to play with it w/o using the foil for lift to see how well it works.

 

The trailing edge wand is a smart and elegant solution, Doug. I have never liked Moth wand system because too long, big and intrusive. And that rod gizmo on the moth bow is anti-aesthetic too.
Having the wand integrated in the strut/foil assembly gives a compact assembly which can be easily and quickly removed and substituted in case of failures of any type. Moreover, it should be nearly insensitive to pitch (which is a disturbance of the input data for this system), and will react mostly to the heave motion relative to the water surface.

A disadvantage of the trailing-edge wand system is that it increases the response lag, because the surface height is sensed near the stern - when the sea-surface perturbation has already been almost left behind the boat. Sea trials will tell how important and relevant this might be for the seakeeping characteristics.

Cheers

 

Surface Sensors

Thanks, Slavi! The Moth and almost any foiler using bow mounted wands moves so fast that the wave that causes the wand to react is past by the time the mainfoil flap reacts. Nonetheless, you might be interested in two short commentaries by Tom Speer on the previous page, post 2465 of this thread.
Many of the Moth people are convinced the bow mounted wand is the only way to go and any other system is wrong. I might have been convinced by some of that if I hadn't had the great good fortune to discuss wand placement with Dr. Bradfield in person several times and in depth. He was convinced that the wand should touch the water near the boats center of gravity and should react to heave input only-not heave + pitch. He felt that pitch coupling was a bad idea. And that pitch should be controlled with the rudder T-foil.
He based that on studying early foilers that used forward mounted wands/surface sensors like Philfly and others.
But the results in the Moth class seem to indicate that the bowsprit mounted wand does work-Tom explains it a bit in one of his commentaries.
The fact is that the midship wand pioneered by Dr. Bradfield and now by Ron Price(designer of the F101 and Whisper cat) works well and has been proven .
Check out Toms stuff-I'm sure you will find it interesting.