Small trimarans under 20'

What an awesome little yacht, a veritable Tardis !
I'm looking for more info on this one !

Good find DL.

 

Doug, I fixed the link, and just checked the numbers on the Mod 70 vs the proposed 18 footer, and the L/B ratio for the 18 footer is 1.286, and the ratio for the Mod 70 is 1.273. Pretty close if you ask me, Not sure if that has much of an impact. Probably more to do with the righting moment, some of which is provided by the crew sitting out on the edge of the boat. Takeoff angle becomes more an issue of crew comfort, as it has a full canting rig.

 

There was an interesting small tri designed to use a Cherub dinghy as the main hull. Never saw much more than this. Definitely had too narrow an overall beam:
click-
Found more on and older thread: http://www.boatdesign.net/forums/mu...l-tri-s-10-14-why-not-33417-8.html#post386079

Picture-Banshee Ambulance w/o amas:

 

I am posting this here as it mentions foils. But check your latest comments on the non foiling thread and then Doug, just to clarify, are you saying that a boat fitted with foils will never capsize? as that seems to be the implication of what you are saying.

Like most people I rarely read your own thread, because there is nothing new in it. But I had a quick look back through and saw the photos in post 1892. Could you clarify what is happening there. Doesn't look too stable to me and unlikely to be a "child friendly" boat. Indeed I would think even I would have a job staying on board at those trim angles especially if I was on the outrigger

RW

 

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Richard I will answer your questions and "observations" about the two pictures(below) in my thread-you know the one you never read. If you had read any of it after the 2nd video you would know the answer(s)! I spent a lot of time learning what happened in the 2nd video and correcting it for the 3rd and 4th videos. I spent a lot of time trying to explain the design and problems with the design after the second video. Had you even read a few paragraphs of that you would have known the story of those two pictures.
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No, that is not what I'm saying. The fact is a well designed trimaran using hydrofoils for full flying or "foil assist" will have much greater capsize resistance when sailed well, much greater pitch resistance than a "normal" seahugging trimaran. It will be able to efficiently use wider beam and more sail area and will have less chance of capsize or pitchpole than a tri using the same power and beam would with no foils. The best and most capsize resistant trimaran foil configuration, in my opinion, is one with a rudder T-foil and T-foil on the daggerboard combined with either a "C" foil on the ama or an Uptip foil on the ama depending on whether the boat is designed for full foiling or foil assist. Ama design is wide open and there are a couple or three major options: 1) small planing ama connected to the boat with high dihedral cross arms and a "curved piece" containing buoyancy about equal to that in the ama hull using an Uptip foil, 2) a "normal" ama using a "C" foil, 3) a "normal"ama using an UptiP foil. Not using an ama foil is a mistake, in my opinion, particularly on wide, performance tri's.
Ama foils on big tri's have proven to improve seakeeping, speed and safety and more and more they will be used and are being used on small tri's. Foils
offer tremendous improvements in ride qualtity, speed, handling and comfort on small tri's and we will see this more and more. The most exciting new tri that I know about is the Exocet 19 using UptiP ama foils and T-foils on each ama. Unfortunately, it will still have the problem of flying the main hull in light air and it is ,basically, a catamaran configuration that doesn't take as much advantage of the basic trimaran platform as it could.
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Richard, here is a link to the answer to your "observations" of the Fire Arrow in your last post: post 1912 http://www.boatdesign.net/forums/mu...f-righting-trimaran-test-model-36058-128.html

Exocet 19 with UptiP ama foils and T-foils on each ama in a catamaran configuration and the two pictures Richard referred to as seeming to be representative of the Fire Arrow-see my response in the link above:

 

Using foils is all well and good when things are going well, its when things suddenly turn nasty that when they become a liability. Yes I agree that when sailed well, they can make a whole difference to the fun and safety factor when at speed. But aren't our expectations that all people can sail all of the time, well, just a bit optimistic.

This year I've probably only turned my cat over less than a handful of times ( either I'm really good or I'm not racing hard enough ). Three of those occassions were of a type that can only be explained by " what happened there ". The reservoir I sail on has very large Jumbos jets flying on approach into Heathrow over it, quite low. Often they cause total 360 degree change of wind in just a few seconds for only a few seconds rather like mini typhoons. At that stage you know you going to get wet as you simply can't depower nor get your self onto the correct side of the boat in that time.

Now having been struck a few times by such wind eddys off rocky points for example, if I'm steaming along at 20 knots and hit such an eddy, try to gybe off away from the rocky point on my port and the foil and small Ama on the port is now under water due to the sudden change in wind direction, what chance will I have of being able to gybe off, probably none.

Good seamanship is not just about predicting weather but also understanding your boat. My worry is that foils will bring a false sense of security to the average sailer and when things do go wrong, it will go wrong doubly fast and doubly as wrong.

The other misconception of foiling is that there will be more broad reaching and downwind to maximise the advantage of the foils. Fast boats push the wind further and further foward the faster you go ( apparant wind ), you basically end up going up wind most of the time. The A Class are finding this at the moment, the benefits of downwind are only just better than the upwind losses. I'm sure that will change in time but to slower boats such as our relatively heavy for foiling, Tri's, the foiling gains are going to be minimal over say a 2 hour out and return with the foil drag on the upwind section semi negating the downwind gain where you can fly the hulls.

With foils there is a long way of development ahead, is it ready just yet for the average weekend Tri sailor, mmmm I'm not sure.

 

Wayne, the biggest advantage of a well designed tri using foils designed specifically for it is when things turn nasty all of a sudden!
Too little is understood by most people about the improvements in handling and seakeeping with this kind of tri-but those improvements have been proved time and again on large tri's in the worst conditions.

 

Doug, you are failing to also say that these big Tri's are skippered by professional sailors and that the Ama's are in the 200% volume range. Even so they crash and flip all to often but I guess to win races one has to live on the edge.

What we are talking about here is amatuer sailors with Ama volumes probably getting nearer 100%, totally reliant on foils and water speed across the foil to maintain the equilibrium. Yes I get the T Foil rudders ( been using them myself since 2002 ) I get the foil assist on a 150% amas, I just don't get the bit of total reliance on foils to be safe.

I guess time will tell, when did you say you were going to build this boat of yours to prove your theory ? and please don't respond saying it has been proven with your model.

 

More and more tri's will be built using foils for "foil assist". The guys that sailed the big boats are the ones that say that foils have increased not only speed , but seakindliness and safety. It's a fact -not speculation. The "theory" doesn't have to be proven-it already has been many times over. No one has suggested "total reliance on foils to be safe". What has been suggested is the use of foils to improve speed, handling, comfort and safety. That kind of use of foils has been 100% proven. But nothing is a substitute for basic seamanship-all foils do is help with control of the boat. Ama size and type is wide open with foil usage-a basic foil configuration with a rudder T-foil and ama "C" foils can make a huge difference regardless of the size of the ama. The MPX foil system being tested on the Fire Arrow shows signs of being a significant improvement over that basic system.
This is Martin Fischer talking about the benefits of foils on a 40 footer-those same benefits are possible on 20' and under trimarans:

I am Martin Fischer. I designed Jessica Rabbit together with Benoit Cabaret and John Levell. First of all I want to correct something. Further up in this discussion someone wrote that we had reported 40 knots of boat speed. That is not correct, so far our top speed has been 33.1 knots in about 19 knots of wind, two sail reaching on flat water. We have rather regular trade winds here in Noumea and while broad reaching we achieve regularily 30+ knots of boat speed.

We are still "discovering" the boat, but we are getting better at sailing her. Jessica Rabbit has - for the size of the boat - relatively large foils and she has T-rudders. This combination of big foils with T-rudders stabilises the boat very nicely. So far we never have had any critical nose dive situation or any kind of pitch instability.

We sailed the boat once with normal rudders in about the same conditions as on the video. The difference was quite dramatic. Broad reaching the boat was much less stable. Average speed was about 2 knots lower and top speed more than 3 knots lower.

Upwind the boat is pretty amazing for a 40-footer. Up to about 16 knots of wind we are doing 14 to 15 knots of boat speed, which is what we expected. But in 18 to 20 knots of wind the boat suddenly steps on her foils while sailing upwind and boat speed increases instantaneously from about 14.5 kts to 17.5 kts. This was achieved with a true wind angle of about 44 to 45 degrees.

Pictures of Jessica Rabbit: (basic foil system with ama foils and rudder t-foils on each ama)

 

There is a big difference between the requirements of a 20 footer and a 40 footer. We're talking under 20 foot boats on this thread so lets limit it whats apt for a 20 footer as I don't think the foil requirements are the same. Lets compare apples to apples and list the under 20 ft Tri's which have sucessfully used foils which has a mixed use other than just speed or racing.

I am not saying it can't be done as I think in the not to distant future we will see them regularly, but until we see the reliability improve ( just the upkeep of the critical foil shape would be a bind ) then we are still someway down the road from really seeing them on the type of boat this thread set out to high light.

Martin Fischer is probably one of the best designers in the world of boat appendages and yet he couldn't get his A Class design to perform, it was actually slower around a course than a sea hugger and has already been binned. I think even he would consider its a tough nut to crack.

 

Martin Fischer has tried many experiments but his latest design the GC 32 is a rocket ship flying on foils faster than any 32 footer has ever gone.
You're wrong about foils: the same benefits that accrue to a fourty footer are perfect for tri's under 20'. Just like fourty footers use daggerboards and rudders that work the same on under twenty 20' so do vertical lifting foils. The value of lifting foils doesn't diminish as a boat gets smaller-if anything their value increases.

 

The GC32 is a much different boat to that of a 20 foot Tri, its a pure racing class that is designed to be as efficient as possible with a very large rig and sail area. That is definately not apples to apples. It is comparible to Jessica Rabbit not a 20 foot Tri.

If we loaded say 10 adults and their lunch onto the GC32 would it still fly on its foils, probably not. Could you single hand a GC32, probably not. With our 20 footer we are asking it to not only sail single handed but that it can loaded with 4 up and their lunch and over night kit.

Its a big ask and foils are just part of the design. There would be far more gain from efficient rigs and efficient large volume foil assist Amas, than to advocate advanced foils.

 

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I wasn't comparing the GC 32 to anything-just mentioning that Fischer designed it and that it works great after you dissed his A Class efforts.
Efficient rigs and a well designed boat are prerequisite for using foil assist on any boat. Large volume amas are not. Advanced foil designs, that help fly the main hull in light air, are likely to have all the characteristics I mentioned earlier with a gigantic leap in the "fun factor" directly related to flying the main hull in a 5mph wind on up. Flying the main hull in light air is one of the biggest benefits possible with simple, advanced foil systems. As the wind increases,it gets the main hull out of the water in waves making for a much dryer and smoother ride as well as controlling the angle of heel of the boat and adding RM in gusts.
The biggest difference between an advanced foil system and basic foil assist(rudder T-foil and ama foil) is a wand controlled foil on the daggerboard that makes a profound difference in how the boat sails, in the "fun factor", in light and heavy air performance,safety and control.

 

I think you need to check out the history of Cheekee Monkee, the F31, eg here

http://www.f-boat.com/pages/news/F-31newbeams.html

original owner Kim Alfred is an excellent sailor with money to develop his ideas. He currently sails A cats very fast. But later CM owners had lots of problems

When I did the 3 Bridge Fiasco on the F27 it was windy, up to 30 knots. The boats in contention were the "conventional" ones. The mini AC foiling types came nowhere. Maybe too much wind, maybe not enough skill, maybe not enough time in the boat?

For remember we are not professional sailors who sail all week, every week, learning how to foil in different conditions. We may only go out once a year in 20+knot winds and sail our boats maybe 20 times a year on average (I sail more than that as does WM) but Doug, for example, how many hours did you sail last year?

RW

 

I am sure WM has sailed at Marconi on the Blackwater. I was there in the spring watching a race. In the first race the foiling Moth overtook a Nacra 5.8 that was flying his asymmetric. Very impressive and proved the Moth sailor knew how to sail his boat

In the second race the tide had turned so there was now a steep wind against tide chop. The Moth didn't make the start line. Every time he tried to go across the chop the foils would be in one wave and the wand in another. After 4 capsizes he gave up

RW