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

[Skyak]

I may never be able to do it but I've come to the point where I want to build a small-around 14'- tri that I can sail singlehanded. I've learned a lot about the new foils developed by Hugh Welbourn for the Quant 23 and Flo 1 and they have a lot of potential to be applied to a small trimaran.
For a 14 footer the platform could be 8' wide eliminating folding and any assembly of the amas to the rest of the boat. The foils would extend outboard about 3-3.5' on each side and be fully retractable for trailering. They would not need to be retracted from tack to tack or gybe to gybe.
For use as part of the basic Fire Arrow concept, they have three great advantages:
1) they add tremendous righting moment,
2) they develop vertical lift capable of supporting the whole boat,
3) they don't develop lateral resistance like most other hydrofoils do.
The 14 would use a wand controlled(or surface piercing) main foil attached to the daggerboard and a rudder T-foil. These foils would work just like they do on the Fire Arrow Test Model controlling the pitch of the boat and ride angle of the outboard foils. But their main contribution is facilitating light air takeoff which would be targeted at around 5 mph(4.38 knots).
If the Welbourn type outboard foils were used without the daggerboard foil the whole boat wouldn't fly until 12-15mph of wind because of the great righting moment of the boat. And that's not acceptable to me.

Here are the foils about to be tested on a 51" model loosely based on Dominion(the first tunnel hulled scow) and on the Quant 23 foil system. The 14' trimaran platform using these foils with the Fire Arrow concept would be for the same length twice as wide as this boat + the foils:

D2 with "B" rig:

You recognize that you have too much righting moment for low wind foiling -so narrow the design to address the root cause. Adding a T foil brings more cost and problems.

It also occurs to me that the model in these pictures has most of the attributes you want or need. It requires more finesse to get up, but that will keep the boat interesting to sail and it will automaticly recover in a capsize.

 

[Doug Lord]

Fire Arrow Variation

The Fire Arrow concept using Welbourn foils should work real well in light air and heavy air and would have the power to be fast as well. I think using the Welbourn foils on a small tri is a good way to have a relatively narrow platform for a 14' tri(8') but have the power to carry sail of a much wider "normal" tri.
The lifting main foil has advantages in addition to allowing the boat the boat to lift off in light air-including enhanced pitch control.
If the beam was reduced to allow the boat to fly without the main foil* it wouldn't allow the sail area of the tri or allow the crew to just sit-he or she would have to hike and/or use a trapeze. The tri configuration with the Fire Arrow main foil allows the crew to be able to sit comfortably while sailing very fast or very slow.
* beam would have to be a little under 4' if the model in the picture was scaled down to 14' but it would be a blast to sail if you could hike and/or use a wire.
Thanks for taking a look at the idea.......

 

[Skyak]

The Fire Arrow concept using Welbourn foils should work real well in light air and heavy air and would have the power to be fast as well. I think using the Welbourn foils on a small tri is a good way to have a relatively narrow platform for a 14' tri(8') but have the power to carry sail of a much wider "normal" tri.
The lifting main foil has advantages in addition to allowing the boat the boat to lift off in light air-including enhanced pitch control.
If the beam was reduced to allow the boat to fly without the main foil* it wouldn't allow the sail area of the tri or allow the crew to just sit-he or she would have to hike and/or use a trapeze. The tri configuration with the Fire Arrow main foil allows the crew to be able to sit comfortably while sailing very fast or very slow.
* beam would have to be a little under 4' if the model in the picture was scaled down to 14' but it would be a blast to sail if you could hike and/or use a wire.
Thanks for taking a look at the idea.......

I don't accept your conclusion that a narrower -lets call it buoyancy beam- boat would not be able to carry enough sail for low wind foiling. You could just have a lite wind rig for those days. In addition to the cost of the extra wide beam boat the self righting/self rescue gets much harder and much heavier. For hiking I would keep the skipper in a sliding seat from edge to edge of the main hull.

Since I have been talking to you about making a boat I can't get a picture out of my mind. It's a narrow planing hull like an IC, with big foils that dip down several feet away from and below the main, then v back up to the surface where there is a small torpedo float. It's like the new windrider foiler but the foil is so large it serves as the aka. What we are trying to accomplish -flying- is so weight sensitive we can't afford redundancy. The floats are only there to keep the boat upright until the foils take over at speed. Another thought I had would be like the UFO -two T foils on a small inflatable float cat, but the main foil is large with independent trim tabs controlled by wands on the outside of each hull adding stability.

 

[Doug Lord]

Fire Arrow Variation

I don't accept your conclusion that a narrower -lets call it buoyancy beam- boat would not be able to carry enough sail for low wind foiling. You could just have a lite wind rig for those days. In addition to the cost of the extra wide beam boat the self righting/self rescue gets much harder and much heavier. For hiking I would keep the skipper in a sliding seat from edge to edge of the main hull.

Since I have been talking to you about making a boat I can't get a picture out of my mind. It's a narrow planing hull like an IC, with big foils that dip down several feet away from and below the main, then v back up to the surface where there is a small torpedo float. It's like the new windrider foiler but the foil is so large it serves as the aka. What we are trying to accomplish -flying- is so weight sensitive we can't afford redundancy. The floats are only there to keep the boat upright until the foils take over at speed. Another thought I had would be like the UFO -two T foils on a small inflatable float cat, but the main foil is large with independent trim tabs controlled by wands on the outside of each hull adding stability.

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Thanks for the comments...
That wasn't my conclusion. The narrower boat would require hiking , trapeze or sliding seat whereas the tri configuration allows very comfortable seats with back support and limits the movement of the crew.
As far as righting the boat it would be designed like the Fire Arrow with high dihedral to the crossarms and two-stage amas that keeps buoyancy high which makes it very hard to capsize in the first place and much easier to right if you do. The total buoyancy of the two stage ama(see below) is less than the weight of the boat which makes it far easier to right. It is possible to design the boat with ballast in the daggerboard to facilitate self-righting if that was important.
Another benefit of the wand based main foil is the gust response of the foil system: when a gust hits and tries to heel the boat beyond its designed angle of heel-about 10 degrees or so- the wand instantly moves the flap up causing downforce until the gust lets up. This is a major advantage of the Fire Arrow foil system which is 100% automatic.(see post 2343)
One thing, among many things, that the Quant 23 proves beyond a shadow of a doubt is that extra weight, in and of itself, is not a deterrent to foiling as long as it's a part of a carefully done design that provides the sail area and righting moment necessary for foiling. Another myth is that all foilers need to be built out of carbon fiber to be light enough. The Quant foiling keelboat is mostly glass and foam and the new Waszp is glass, foam and aluminum.

 

[Skyak]

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Thanks for the comments...
That wasn't my conclusion. The narrower boat would require hiking , trapeze or sliding seat whereas the tri configuration allows very comfortable seats with back support and limits the movement of the crew.
As far as righting the boat it would be designed like the Fire Arrow with high dihedral to the crossarms and two-stage amas that keeps buoyancy high which makes it very hard to capsize in the first place and much easier to right if you do. The total buoyancy of the two stage ama is less than the weight of the boat which makes it far easier to right. It is possible to design the boat with ballast in the daggerboard to facilitate self -righting if that was important.
Another benefit of the wand based main foil is the gust response of the foil system: when a gust hits and tries to heel the boat beyond its designed angle of heel-about 10 degrees or so- the wand instantly moves the flap up causing downforce until the gust lets up. This is a major advantage of the Fire Arrow foil system which is 100% automatic.
One thing, among many things, that the Quant 23 proves beyond a shadow of a doubt is that extra weight, in and of itself, is not a deterrent to foiling as long as it's a part of a carefully done design that provides the sail area and righting moment necessary for foiling. Another myth is that all foilers need to be built out of carbon fiber to be light enough. The Quant foiling keelboat is mostly glass and foam and the new Waszp is glass, foam and aluminum.

I am saying I think a boat can be designed to foil without hiking on a trapeze.

The MPX is designed to be 100% automatic -at some cost and complexity. I think there is a cheaper, more desirable solution that is not automatic but easier than the bi-foilers.

You seem to be trying to put me on the opposite side of a foiling argument -I am not arguing against you -I am suggesting that a foiling boat could be made out of wood and aluminum.

 

[Doug Lord]

Fire Arrow Variation

I appreciate your comments. The most important thing to me, if I build this Fire Arrow Variation, is to enjoy the boat and the unique characteristics it will have. Those characteristics are important to me and would heighten my enjoyment of the boat. One of the most important is comfort(w/back support).
Another is that it be very easy to foil starting in very light air. The more automatic the foil system the better. The elements that make the system automatic are among the least costly components on the whole boat and are extremely simple.
I've built dozens of boats over the last 50 years and I think I may have one more left inside me. But it may be out of my hands-time will tell.

 

[Doug Lord]

Fire Arrow Variation

You seem to be trying to put me on the opposite side of a foiling argument -I am not arguing against you -I am suggesting that a foiling boat could be made out of wood and aluminum.

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Certainly not my intention.......

You're 100% right.........

 

[Doug Lord]

Fire Arrow Variation-foils,again...

Since I first saw the Quant 23---and understood how the foils worked-- I've considered using these foils on a small tri. Whats real different with these foils
is that they don't develop lateral resistance like UptiP foils, T- foils and most other surface piercing foils so they can be 100% retracted for sailing in very light conditions or, for that matter, any time you don't want to use the ama foils.
On a boat like the Fire Arrow Variation at 14' the main daggerboard/t-foil provides all the lateral resistance for the boat and it can be mostly retracted when you need to.
The Welbourn type foils are an interesting foiling solution because they develop a large righting moment and vertical lift with no wands or frequent manual adjustment-basically set it and forget it.

 

[Doug Lord]

Fire Arrow Variation Testing

The Fire Arrow Test model is an exact scale model of a 19.5' sport trimaran.
However, if I change the scale to make the overall length 14' and make new amas that plug in just like the current Test Model amas do, then the "new" amas would allow the Welbourn foils to be tested in place of the current UptiP ama foils. And I have a mold that could be used to lay up the new amas very lightly. Wouldn't cost too much to do this, I don't think and would be a great test of the application of Welbourn foils to a trimaran-at least until a full size version could be built.

 

[Doug Lord]

Fire Arrow Variation

One of the design features of the 14' Fire Arrow Variation would be extremely comfortable seating on each side and a relatively comfortable "bench" seat at the aft end of the cockpit. The seating on each side allows a 200lb person to move a bit fore and aft as well as sitting comfortably. The side seats would be quite low-at least they would seem low because of the high dihedral of the crossarms. The sensation would definitely be one of sitting "in" the boat rather than "on" the boat. The boat would be designed as a singlehander with comfort as one of the main priorities.
Because the boat will foil in such light air it will always be pretty dry in the seating area and the view should be outstanding.

 

[Doug Lord]

Fire Arrow Variation and Fire Arrow

One of the things I haven't mentioned in a long time is ama buoyancy vs total boat weight but I saw it mentioned in an article posted by TT in "Small Trimarans Under 20'". John Perry designed a 19' tri which has adjustable amas so they can be raised or lowered. But he also designed the ama so that it would not float the boat in a capsize. Thats also true of the Fire Arrow where the total ama + "curved piece" buoyancy is less than the weight of the boat(see post 2359). The reason for doing that is so the thing will not turtle and it also makes it much harder to capsize due to the two stage ama and high dihedral crossarms.
The Fire Arrow Variation would also have these features though the platform is proportionately narrower than the Fire Arrow. Both the Fire Arrow and the Variation, of course, are foilers and so the reduced buoyancy has no effect on sailing the boat-especially since both boats will fly in around 5 knots of wind or less.

 

[Doug Halsey]

.. But he also designed the ama so that it would not float the boat in a capsize. Thats also true of the Fire Arrow where the total ama + "curved piece" buoyancy is less than the weight of the boat(see post 2359). The reason for doing that is so the thing will not turtle and it also makes it much harder to capsize due to the two stage ama and high dihedral crossarms.

Another reason for doing that is so, when the boat does capsize, the main hull will be floating at the water level, rather than way up in the air. I think that's a pretty significant safety feature.

 

[Doug Lord]

Fire Arrow Variation and Fire Arrow

Another reason for doing that is so, when the boat does capsize, the main hull will be floating at the water level, rather than way up in the air. I think that's a pretty significant safety feature.

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I agree but there is a problem with a boat like the Fire Arrow: it is 22' wide so if it were ever to reach 90 degrees it would more than likely hit bottom on the way*. Much better with the 14' Fire Arrow Variation that has a platform beam of only 8' (Welbourn foils retracted). If the boat were to capsize with the Welbourn foils deployed it would need more than 7.5' of water to have the foils clear the bottom. That may be a problem but the key probably is to make it very difficult to capsize in the first place-and the high dihedral crossarms and "two stage ama" will help with that.

*it would never reach 90 degrees in most places around here!

 

[Doug Halsey]

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I agree but there is a problem with a boat like the Fire Arrow: it is 22' wide so if it were ever to reach 90 degrees it would more than likely hit bottom on the way*. Much better with the 14' Fire Arrow Variation that has a platform beam of only 8' (Welbourn foils retracted). If the boat were to capsize with the Welbourn foils deployed it would need more than 7.5' of water to have the foils clear the bottom. That may be a problem but the key probably is to make it very difficult to capsize in the first place-and the high dihedral crossarms and "two stage ama" will help with that.

*it would never reach 90 degrees in most places around here!

Where I sailed Broomstick most of the time, the water was 90 feet deep (at least before the drought), so hitting the bottom was never a problem.

And with zero-dihedral crossarms, the boat was tremendously stable when turtled. So much so, that in order to right it, it was necessary to remove one ama. Fortunately, that only happened with my smaller set of amas, which were attached just with bungees.

 

[Doug Lord]

Fire Arrow Variation and Fire Arrow

Its so shallow here-do you have any ideas how I could deal with that better than I already am?
In the first tests(2nd day) with the Fire Arrow model, I had inadvertently made the main foil wands too long and the ama foils didn't have enough area. And the rudder on the boat had too much authority. The result was that the thing would jump clear of the water, pitch up and mush back down as the foils stalled and even though that second test overpowered the rig substantially no capsize -not even close. However, she did do a beautiful 45-50 degree pitch pole*, righted herself and sailed away. The "two stage ama" and crossarm dihedral allows there to still be lots of righting moment up to and a little past 90 degrees.

* skippers fault