18' Trimaran vs F18 Catamaran

Hi Dough,

I know a guy with a windrider tri who added a considerable length to his mast. It was a lot faster in low winds, but the problem was always that the ama's buried at speed, and when the wind is up good even the main hull started diving. My one friend also has one too, I can sail it right under the water.

It has the std bermuda main sail, which is probably the problem. The wind pushes it down into the water, best speed I got out of it was about 23km/hr.

Now if I was to get the speed up, I'd use an aft mast setup that would produce lift, the harder the wind, the more lift. You saw the sail I used on my little tri.

Any way, just some comments.

 

Fanie, I'm not sure I remember the sail on your little tri-I'd like to see it if you could post it....

 

Also a link here http://www.faze.co.za/Little Tri/Little Tri 4.html

 

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Nice! And I have seen that cool little tri before. How does/did the sail work upwind?

 

You want the foot of the sail taunt for upwind, that's why I added the boom. My arms was too thin to to wrestle the wind and keep it there. I never measured the exact angle to wind, but it gets a lot better with the boom. The closer to wind you go the slower, unfortunately to a point where it stops It also tacked a lot easier. There is a balljoint on the boom end connecting it to the deck. If the sail points aft the sail foot is taunt. If you run the foot end bends some. Worked ok.

I haven't done enough experiments - too bloody poor, but there defenately is merrit in this sail setup. One thing I really would have liked to do was to add more leading edges in the same sail, considerig it is the leading edge propelling foreward (and up).

 

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You're sure right about that. When the facts are ignored that show the trimaran to be smaller physically than the cat-in terms of the hulls and when the cost estimate made in the post on the previous page is discounted even for a production level similar to a Hobie Wildcat then the actual facts are not being considered.
The major point of the thread was to illustrate that by adapting modern technology( foil assist/altitude controlled lifting foils+ planing hull or DSS for the ama's)
to small trimaran design a boat could be built that would be faster than an F18 that would require very little crew effort to sail fast. A boat that could be sailed at MAX power virtually regardless of crew weight.
It is a new type of trimaran that can be adapted to almost any size under twenty feet with similar benefits so far unheard of in current small tri design.

 

Arent you really just saying that if you increase the beam you dont have to hike as hard?? (or use traps to be more specific). Surely at this size, for a similar build method a cat will always be lighter and cheaper to make.

Another point to consider from a practical standpoint is that there will be a considerable physical effort required to trim this boat (really anything with this sort of sail area), this may be more limiting to market entry so to speak than using traps, which incidentally make it easier to trim as you can use you body weight and legs to help sheet as well.

 

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No. Increasing the beam is a two edged sword. If you increase the beam with a traditional trimaran design you would have poor light air performance since the boat would have so much RM that it would not want to fly the main hull*-which is absolutely critical. If you designed the boat to utilize traditional trimaran amas you would have a boat thats too heavy. The use of foils on the main hull solves the pitch problem as well as providing for early takeoff and a wide crew weight range since the foils will automatically pull down or lift up as necessary. In addition, because of the foils and their control of pitch, a small planing hull is likely to have real potential benefit since the running angle of the planing hull is controlled by the main hull foils. A more "traditional" ama utilizing DSS instead of curved banana foils has the advantage that the foils would be lifting in only one direction since the heel angle of the boat is automatically controlled by the altitude control system(wand) on the main hull.
I completely disagree in terms of weight. It has been shown earlier that the physical size of the three hulls is smaller than the two hulls of an F 18. The weights projected are based on a similar build method but a high tech build would reduce the weight of the tri to less than that of an F18. Note earlier that a Marstrom 20 is 154lbs lighter than an F18. In terms of cost the tri is likely to cost a bit more than the F18-I think my estimate earlier is in the ball park for a similar production level. The key here is the use of small ama's and foil assist without which the tri would not work.
As to the "physically demanding" aspect of sheeting the sails ,I'm afraid I disagree again: if a single man or woman can sail a 60-70' trimaran around the world surely we can come up with a suitable, not physically demanding, sheeting system for this boat.
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This concept has been applied to a much smaller 12' tri with loads of detail ,if you're interested in a further understanding of its benefits and potential here:
http://www.boatdesign.net/forums/multihulls/mpx-11-very-small-high-power-trimaran-33686-3.html

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*As an example, the tri with a 240 lb crew sitting 18" to weather of the CL of the boat would have a RM of 5320 ft. lbs and in a 15-17 knot wind the heeling moment(277 X 15=4155) would be 4155ft.lbs. Cheesy,this is absolutely critical to understand this concept because it can cause a trimaran to be slow over the most used segment of the wind range. If a small tri, designed for high performance, does not fly the main hull it has too much drag,period. The foils on my tri concept overcome this drawback letting the main hull fly in as little as 5 knots of wind.

 

Again it is in front of us, Doug Lord. You compare the apples to the oranges when it comes to numbers for comparison. Marstrom is small volume, yes. Hobie is not so small volume. Still it is small when talking of boats built. M20 is critical carbon boat having bag and autoclave build with ultimate strict attention to technical points. Hobie Wildcat is not so strict by many points.

Here, you try to compare them as indicator of conversing. they are not same. Take the one and live with limit in argument. making two very differnt boats to say your argument is problum. They do not match this way.

Cheesy has correct. tri will always cost more for same length of boat. Boat makers in world do have this complete idea, why do not you? If tri can cost the same, there are to be many more trimaran boats in process than there now. There are not, so someone understand this problum and you have not that same knowing.

Please if you will. find other argument. this one you make is not strong at all. even as foreign person I see this wrong talk. why do not you come to knowing as well. now this talk is second time joke coming after little baby boat that is not real.

 

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44, you have either not understood what I have said or ,perhaps, choose to ignore it. I apologise that I don't seem to be able to explain the relationship of the physical size of the boat to its cost in relation to an F18 to you.
This is a prime example: I have repeatedly pointed out that the amas on this tri are not like the amas on a "normal" tri-they are
MUCH SMALLER-and yet you say this.
This is a new concept not used by any other designer anywhere that I know of -and the details are critical in understanding how it functions, how heavy it will be and how much it will cost. I've done my best to try to make that clear.

 

Foil Control System-an idea...

If a tri like the 18 described here used a small ama foil for righting moment-and to fly the whole boat above a certain speed- as allowed in the Concept discussed in this thread, then a question arises as to control of the foil lift with minimum wetted surface and drag in light and heavy air.
One way of doing it would be to use "foil assist" where part of the ama is always in the water, or a surface piercing foil. Some designers use no altitude control at all but that is a draggy set up despite protestations to the contrary. Another way is to use a separate wand for the ama foil-but that would make three wands total since the main hull uses a dual wand set-up like Mirabaud.
This may be the answer: Move the dual wands out away from the main hull. Link the pushrod for mainfoil flap control to the wands via a carbon tube "shaft". The windward wand would be clear of the water, the leeward wand would be controlling angle of heel(altitude). Heres the neat part: run another carbon tube "shaft" to the much smaller ama foil and reverse the linkage! When the mainfoil flap goes up because the boat heeled the ama foil flap would go down. If it works it is a great simplification of a three foil system-all of which have two wands or "feelers" on the water all the time. Hmmm....

 

Hi Doug,

I just looked and I've been 5 years on the forum here. I've seen a few/several/many ideas from you. Have you built and tried any of them? Not trying to be confrontational, just wondering what you have been up to when you are not thinking on paper and posting here.

If you wait until you have what you think is a perfect design, you might not ever build anything?

BTW, as soon as you are sailing on one hull does it really make any difference if the boat is a cat or a tri at the dock?

Moving the CB forward of the CG as the ama load increases should provide a positive response to pitch down, a fixed foil in the same position will have the opposite effect I think. I think this is the reason that the foiling tri's have control systems for the foils?

Cheers

R

R

 

So, there it is.

This is a cogent response to this, "reach back in time" foolishness. Isn't it time to let dead horses lay where they will, Doug? This thread died a long time ago and your eagerness to resurrect this discussion only shows how vacuous one can get when it comes to fresh thinking.

Please stop and let this go back to the place where it once laid in repose.

In the meantime, we have one, Lionel Lemenchois, who has once again won his Class in the very difficult, Route du Rhum without lifting foils of any kind. Perhaps a cogent response to that reality would be in order? Come on, Doug, it's time to admit that fast multihulls do not need to have lifting foils in order to turn in terrific performances. When you get to that place, you will have Crossed the Rubicon of new thinking. It's a process that is long overdue.

 

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Hey, Randy-the post here was to tie in the concept of two foils on the main hull between the 18 and the MPX-12. This is a new application of the use of a bi-foiler arrangement that ,as far as I know, has never been used on a trimaran. The use of the two foils on the main hull with a wand system allows a trimaran with a very small ama with pitch and angle of heel controlled by the main foils. I think it has a great deal of potential.
I'm working on the Trapwing now-with some help-and then hopefully I'll do the MPX-12. What have you been up to?

 

So, Doug, maybe you can show us all some photos of this wonderful progress you have made on the Trapwing build?

Failing that, we can only surmise that you have done nothing.

So, perhaps it is time to haul-out the progress photos on the Trapwing, or suffer the frankness of being full of baloney. Hey, you mentioned it, so one can only surmise that you have something of gravitas to share.