Small trimarans under 20'

Wayne, that cuddy doesn't look big enough for a person to get into to me?

 

Correct, and I would say that one thing is going to be the Pulse's biggest folly.

 

Yes but we are talking of small tris. Accommodations on a 18-20 feet tri are close to zero, or you get a floating box with the hydrodynamics of a barge. On a Tremolino for example the accommodations are extremely cramped...A tri is beginning to be "livable" at 25 feet at the price of a pretty complex and rather heavy shape of the main hull.
In fact on a 18 feet boat it's simpler to put a tent on a cat like did long time ago Mr Herreshof, and I did myself 100 years later. You can get something (crampy) on a 18-20 feet monohull, but on a tri of the same size nope.
I think we are talking more of beach boats, simply by the requisite of size.

SOR Easy to put in water in a sand beach, almost as easy to get it out of water from a sand beach, trailerable with an ordinary 4 cylinders car, easy to set up, easy to dismount. Able to do some raid, and sure enough to survive to the wind generated by a good black storm cloud.
As cheap as possible we are not talking of an all carbon fibre racing boat.
And decent performances, by that word I mean not beaten by one kid on a 12 feet rotomolded catamaran, and not crushed by a 20 years old Dart-18 feet- cat with 10 years yellowed polyester sails driven by 2 sexagenarians, who can't trapeze because of the arthritis.
Most of the tris shown here do not fit yo what I think is a minimal SOR, or too small, or not well engineered/designed, or far too heavy.
In fact it's very difficult under 25 feet to design and build with "ordinary" materials a trimaran competitive with a same size catamaran. It's simply arithmetica. More hulls, more surface, more beams. As the scantlings have to be similar (the local stresses- for example the weight of a fat guy jumping on one foot on the deck- are identical) it's very difficult to manage the quantity of materials thus the weight.
So you have 3 solutions:
1- Low freeboard/small amas (less than 125% of the total weight boat plus crew) that doesn't work. All these tris are bad performers. A bit of wind and the amas become hydro-brakes.
2- Small size to keep the weight manageable. It's a beach toy and frankly a 12 feet rotomolded cat is as boring but far cheaper.
3- Decent size and freeboard but it weights between 60 to 100% more than a similar cat. 320 kg instead of 180-200 kg. I prefer to sail a cat with the handicap of 3 nice girls on the trampoline. Not fast but funny.
To have a "fast" tri you must be able to get the main hull out of water, not a lot just skimming on the surface, that means amas with at least 150%, 180% is far better, of the total weight. For a 320kg tri with 2 guys that means
(320+160)*1.5= 720 liters of volume. That's very big for a 18-20 footer ama...far bigger than the size of a Tornado hull.
Conclusion; the 320 kg tri will be a slow one, unable to follow a simple 18 feet cat. Nice and comfortable. Expensive surely because 320 kg of material is always more expensive than 180.
I won't talk about righting up a tri of this weight. With just the crew is pretty complicated.

 

For the same price and weight of a 20 feet tri you can have a more spacious 23 feet cat with floor, cockpit and seats, with enough place in the hulls to sleep the children when tired...You're talking about a family boat. And it's always trailerable. A guy made that in plywood in France in the 80ties, sailing with wife and kids. Besides it was an excellent fishing boat with a 10 or 20 hp outboard and no sails.

 

Quote:- In fact it's very difficult under 25 feet to design and build with "ordinary" materials a trimaran competitive with a same size catamaran. It's simply arithmetica.Quote.

I disagree entirely.
Take a popular but simple Tri. The Buccaneer 24.
I owned one , and it, with others built and sailed by other people, would blow the doors off similar and larger sailboats of ANY configuration. Being of ply construction it certainly was of "ordinary" construction, and for it's speed did not require sailing on one float.
In my sailing and building career I have owned 6 monos, 5 cats and 4 tris, all but one under 25ft.
The tris beat the others, hands down, in all respects.

 

High Performance Under 20' Trimarans

Paddy, in the EC2014 a 20' tri(Sizzors) beat a Tornado or two. Unfortunately, tri's have a bad rap under 20 '-especially 12-18' for being slower than beachcat's.
Just like from 20' on up where tri's have often dominated cats the same could be true with smaller boats if designers took advantage of the opportunities the trimaran platform offers. It amazes me that there are virtually no small high performance tri's. The Exocet 19 might change that if it gets completed and so might my Fire Arrow if I can get a full size version built.

 

And the Buccaneer is 24 feet not 20, it weights 2000 pounds. A good boat but I won't call it a beach sport boat. So it has nothing to do with the SOR of the 20 feet beach trimaran of the thread.
About beating the others, that depends of the opposition. For example I doubt that a Buccaneer can beat a 25 feet Dragonfly trimaran. And we are far from beach boats.
The Buccaneer illustrates fully that 24-25 feet is the lower limit for a tri when working with "normal" materials. A Buccaneer "reduced" to 20 feet is not competitive in front of a Nacra 20. I doubt also that the full size 24 can beat the "ordinary" Nacra 20 or a nowadays Tornado with spi.
A few 25 feet day sailing cats with minimal accommodations were made in France around 1990. Around 500 kg, 45m2 of sail, plus 60 m2 spis. These cats would beat any racing beach cat of the period, Tornado or BIM 20 and were not ridiculous in front of a F40. Far faster than a Buccaneer, but slower than a Flying Phantom.

 

Doug, Sizzor is a totally impractical design sailed by one of the worlds best multihull racers, it would be rather embarrassing for the trimaran movement if it was unable to beat a Tornado which is after all a nearly half century old design. As you point out there are virtually no small high performance designs so of course the beachcats dominate, but is also true that there are virtually no high performance cats in the 20 to 30ft range so of course the tris dominate in this range, this is of course due more to the fact that the trimaran configuration lends itself to easy folding systems than anything else which is why they are more popular in this size, no other reason. The wide beam of a tri is a big handicap getting in the way of them being practical in the under 20ft range. I think that solving the trailering problem would lead to greater popularity, more so than foiling imho.

Steve.

 

Guys you talk of a 20 ft beach racing cat and then immediately compare it to a Tri with a cuddy on, they are different beasts for different purposes. A 20 ft racing cat should be compared to the likes of Scissors which is a dedicated racing Tri. Surely the likes of a small Stryder is probably more the comparible and then you run straight into folding problems and weight.

What a 20ft Tri is going to good for, when the designer gets it right, is a small cuddy just big enough to store your sandwiches, offer a bit of protection if needed and a bit of privacy for the girls. No you won't be able to sleep in comfort in it but then you will almost certainly have a big cockpit which you could put a tent over if needed.

What I surmise a 20 Tri to be, is simply a more shelterered and refined catamaran for day sialing to the next port where I can rent a room for the night. You can rent an awful lot of hotel rooms for the savings made of only a few feet in length. An F22 compared to a Pulse 600, how many dollars saved.

 

20 and UNDER 20

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Sizzor, could be a great sport tri if it was manufactured. A boat very close to it is Ted Warrens Ultra Light 20-under 200lb all up. And in 1969 Victor T -a C Class trimaran beat all the C Class cats.
Addressing the beam issue is quite simple. The Weta solution could be improved upon or a another folding system could be devised(see below). The trimaran platform lends itself to the use of lifting foils for full flying OR foil assist which would allow square or oversquare boats with tremendous power. The foils would allow that power to be safely used downwind. And the result would be a very fast boat.
There is tremendous potential for innovative design in 20 and under tri's.... And I stress "under"-- too much is focused on 20 footer's when a practical high speed foil assist tri could be done from 12'(with a retractable gantry) on up. The most important ingredient, in my opinion, for any small square or oversquare tri is a wand controlled foil on the daggerboard OR a surface piercing T-foil daggerboard(I'm experimenting with this type of foil-it may work very simply). It's not critical to have foils on the ama though it would be faster with them. It's not critical for the boat to be full flying. It is critical to fly the main hull in very light air-5mph.

Sketch- folding system for a boat like Fire Arrow. Design was mine with engineering by Eric Sponberg. Click on the sketch to see the detail of the sliding insert that makes this system workable:

 

Scizzor is extreme (and wonderful) but Randy perches way out there on a tiny platform and your average sailing punter is not going to be impressed with that. Also it is strictly a single hander. Also it is based on a single hull from an A Class cat with a couple of feet added ... so the boat is ultra light, probably lighter than other 20 foot cats or tris around.
I agree with Ilan Voyager, 20 feet is too short and too cramped for a small crew.
OS7 talks of a proportionately shortened B24. I'd like to see the results of a drawing of that because it would be kind of like a fattened Crowther day sailer - and wouldn't perform.
It is an interesting exercise - but a bridge too far.
I'm playing around with an oversquare 6.5m type (so the beam and angled floats can be swung fore and aft for trailering). Inspired by John Patterson's 6.5 (see photograph) - but lighter and maybe faster. I have a few tricky shot cuts. 21ft 4ins main hull is not 20 feet - and it is still a shoehorn job to get basic, basic accommodation and retain respectable performance at the same time.

 

Yep, Sizzor is a completely useless design for anything other than what it is being used for, its great for that in the hands of someone of Randys caliber but probably few others on the planet. I remember seeing in an old multihulls magazine a 21ft foil stabilized monohull that I have long been intrigued by, it looked like a tri with a long skinny main hull and an over square layout with a single crossbeam with fat foam foils on the ends that allowed it stability from buoyancy at rest and hydrodynamic lift under way, but no amas per se, you sat in it like the hobie trifoiler. It seemed to me that with the single beam and being over square you would be able to rotate it around so a foil was across the bow and stern. I liked the concept.

Steve.

 

Fat foils don't work well.
Probably why you don't see one now.

 

Steve, have you ever seen "Blue Arrow"? She was around 60' and exactly as you described except for length. A British AC Challenger:
click-

 

Gary. Please go back and look again at my post #285. I was talking about a tri under 25ft, not 20ft.

Getting back to the nitty/gritty, it is currently typical to run down Pivers designs,------but they are not all bad.
The 16ft "Frolic" was a hot little boat.
Jim Brown was most enthusiastic with his one, dashing about on SF bay. It propelled him into a trimaran design career.

The Frolic had Amas which were literally water skis with sides.
It was very fast.
I built one for my teenage son so he could sail across Lake Simcoe to visit his GF. He would sail it day or night and in all weathers.
I built it with fixed daggers on the amas rather than the central daggerboard.
That allowed a full sized berth in the Vaka under a tarp.
It was still small enough to be carried on the top of my car. (A big Oldsmobile)
It had a "kickup" rudder, self tacking jib, and compared to other small tris was very dry to sail.
I built it in my car parking space in the underground carpark of the high rise apartment block we lived in at that time, and it was a very quick build. Plans are still available from the Maritime Museum.