small trimarans

[casavecchia]

Hi all,
I keep wondering why there is so little interest in small trimarans around 4/4.5 meters long.
They are inexpensive , easy to build, light and cartoppable, sail fast and are reassuringly stable.
Besides , being not so phisical, are well suited to older and /or handicapped sailors.
So why are not more widespread?
Regards,
Marco.

[Stephen Ditmore]

Kurt Hughes has offered some nice designs, but I think the real advantage of a trimaran over a catamaran is its ability to carry greater headstay tension. At this size, jibs on cats are quite small relative to the mainsails, so there's not much need for the third hull.

I think an open center hull would be nice, though. It'd make a nice fishing boat for some areas (developing countries, etc.)

One could convert an International Canoe to a trimaran. Come to think of it, the WindRider Rave and the Hobie TriFoiler are basically trimarans.

See:
http://www.windrider.com/wrrave.shtml
http://www.hobiecat.com/sailing/models_trifoiler.html

[casavecchia]

With the obvious exception of the Rave and the Trifoiler,
the small trimarans I see on the web are too low on the water and this is so much in contrast with the spydery look of the big racing trimarans. The small ones dont trasmit the impression of agility and nimbleness that their bigger brothers suggest. May be that's the reason for their scarce appeal. Anyway they are a good platform for testing hydrofoils. They are easily and cheaply built in plywood, sharpie style, and lend themselves perfectly to workboat use.
Marco

[terhohalme]

Junk Proa has less to build than trimaran and have all the goodies.

[grob]

After we have completed the X-Cat this is to be our next project

http://www.fourhulls.com/frames.htm
http://www.fourhulls.com/pics/tri.gif
http://www.fourhulls.com/animate/trian.GIF


Gareth
Warob Marine
www.fourhulls.com

[Doug Lord]

I've always loved small tris. (and other multi's as well.) I built a 14 and 20 footer with planing main hulls years ago.
I haven't seen any small tris 20' and under- that take full advantage of the potential of the tri. The big 60 footers are square and yet the smaller tris all seem to be much less than that.
A small tri can develop massive righting moment but the capacity needs to be generated by flying the main hull and I've never seen a small tri designed by anyone doing that (but I'd like to!)
If you consider the realities of pitchpoling that is still no excuse for not using the max righting moment because the use of foils can eliminate pitchpoloing. You don't need a full flying foil set up either to take advantage of all that power.
As was said before a full flying foiler takes good advantage of the trimaran concept but I'm not sure they are the ultimate in speed for small tri's. I think there is a lot of potential with planing hulls on ama's and other combination's of foils and planing hulls.

[Skippy]

Frank Bethwaite's HSP is a small tri, but he doesn't use the lee ama. He hikes out off the windward ama and flies both of them, planing the main hull a lot of the time.

Derek Kelsall discusses the cat/tri issue for large racers here:
http://www.kelsall.com/CatvTri.htm

[Doug Lord]

My 14 was similar to the HSP in that it was designed to have the amas(buoyancy pods) out of the water at top speed.
Lots of potential and HUGE RM availble in small tri's that fly the main hull as opposed to the HSP concept and are at least as wide as they are long...

[henrikb]

I am currently designing a 6.5m tri together with a friend. The main hull is almost completed (beams, floats, rig not final design on picture) and we will start cutting frames any day.
Beam is 5.8m, displ is 650kg fully loaded. Sailarea 33m2 upwind.
The floats will have a volume of aprox. 3*displ, so it will be possible to fly the main hull!

[Doug Lord]

Looks great and sounds very interesting; good luck!

[Skippy]

You have to be careful about separating the flotation and the ballast too far. If you do, you'll have more problems with pitching than with roll. That's one reason a cat's L/B is about 2. All the flotation is at a distance of 1/2 the beam from the boat's CoM on the centerline around a rolling axis, but the average distance of the flotation from the CoM amidships around a pitching axis is less than 1/4 the lwl.

And the moment exerted on the sail by the wind is not directly athwartship even when close-hauled, so as you can see on the aussie racing skiffs, you eventually have to move the ballast aft of the transom! That's why Malcolm McIntyre's 1930s catamaran could be distorted into a parallelegram, lee hull forward.

(slightly modified for accuracy)

[Doug Lord]

I think the utilization of foils such as on the Rave is suited well to a square or over square tri platform since the foils are developing the RM for the boat-and the anti pitching moment.
But with the trailblazing work of the Moth foilers using just two foils that just do the lifting -and pitch control-I've thought about the potential of a small foldable(for trailering) tri say 18'LOA by 18' or so wide. This concept would use the crew for ballast(2) and smallish planing hulls for the ama's and would be designed to fly the main hull.
Small hydrofoils would be used on the rudder for pitch control in conjunction with a small altitude controlled main foil that would lift up as well as down.
So the boat would only have two foils both relatively lightly loaded. The question is can a planing ama on a boat like this be less drag than a fully submerged foil that lifts and develops righting moment? I haven't attempted to answer this question yet but I will at some point.... Any thoughts?

[Skippy]

A foil trimaran is very different from nonfoiled. The foils act kind of like a catamaran, moving the flotation away from the centerline. Whereas the Windrider is for people who just want to sit in the cockpit. My biggest question has always been, wouldn't the planing ama be uncomfortable when you're hiked out on the windward one and it slams down on the water in a sudden lull?

[Doug Lord]

At static the two amas would not touch the water at the same time so in a sudden lull the first thing that would happen is that the main hull would tend to come back down but because of the foil on the daggerboard it wouldn't precepitously drop. Now, in a wind drop from 20+ to zero the windward "ama" might come down first but I doubt that it would be uncomfortable as much as heart poundingly exciting. And I doubt that that is any realistic concern.
This boat ,if built and designed well-and lightly- could potentially compete successfully with small cats. It amazes me that -as best I can tell -a maxed out mini tri hasn't been done yet;at least that I've seen. It would surely be more expensive than a cat but I'd bet it would be faster in light and heavy air. And if the planing amas work top speed could be much faster at least in relatively flat water...

[mattotoole]

I'm becoming intrigued by small tris, for a lot of reasons.

I lived in Australia when I was a teenager in the late 70s. I remember the original Farrier 18' Trailertris well. They were the best daysailors going, certainly more exciting then the Rhodes 19s, etc., we had in the States. They were no harder or more athletic to sail either. Small tris allow a less athletic person to avoid scrambling all over the place, while experiencing very high performance. Of course they're lighter and easier to trailer than any monohull with a keel.

I think Farrier is really onto something. People want to go fast, but they don't want to work hard (or swim, as with small cats). We're also running out of marina space. The solution is drysailed boats, at least in the under 30' range. So 20-30' tris may have a big future.

I've always been intrigued by boats like the Tremolino, which used widely available components (Hobiecats) cobbled together into something simple, low-cost, easy to handle, and very fast. The sharpie-style concept mentioned above is interesting too.

I saw an interesting boat a couple of years ago in Garden Bay, BC. It was a very small, one person tri, with short amas, of rotomolded plastic construction, and about 13' long. It had a simple cat rig, and IIRC it might have been boomless. I couldn't figure it out at first -- why someone would build a boat like that. But then I saw it sailing -- faster than anything else its size. And on a windless day, I really saw the advantage -- it could be paddled like a kayak, at a pretty good clip. Just wrap the sail around the mast, and paddle away. It was probably cartoppable too. Does anyone know anything about this boat? I've seen a couple of sea kayaks fitted with amas and a mast/sail too. Even with a tiny sail, they really moved along.

My dream boat right now is a 24-33' Farrier. I'm curious to see what the promised 22' model will be like, especially if it's more affordable.

[Skippy]

Thanks Doug.

[bfrowe]

That could have been a Hobie Bravo. It uses a boomless, vertical batten, roller furling around the mast, square top sail. The dimensions sound about right. You can see a picture on the Hobie web page. I have been considering it's sail for my little Sea Pearl tri.
Bruce

[bfrowe]

As the owner of a "small trimaran", I have been drinking up all this fascinating discussion about the various configurations available. My boat is too heavy to ever fly the main hull as well as being limited by freestanding masts that won't allow maximum sail areas, but that doesn't mean the boat won't plane under the right conditions. As with the leeboard question; my goal with this craft is to reduce weight and improve the basic systems. Couple of choices for amas: planing or wave piercing. Right now I would classify my amas as wave catching.
Bruce

[Doug Lord]

Can you post a picture of your ama's?

[casavecchia]

When I think of planing amas , I think of fat sterns and this is not the current trend in fast narrow hulls (Int. Moth). I sail a very small (3 meters) tri of my own design.
Amas are pin tails and I feel extremely confortable sinking the stern a bit when overpressed. Vaka and amas are very simple rectangular sections but vaka is square sterned and drags a bit when going slow and in fact I am thinking of building a pin tailed main hull.
Marco.

[Doug Lord]

The major problem with planing ama's is what to do with them in light to moderate air. If that problem is solved the top end speed goes up dramatically. The purely displacement high beam to length ama is going to have a somewhat limited top end speed though the Moth hulls are designed to plane AND have pin tails.They just start to plane at a higher speed..
Can you give any details of your small tri?

[bfrowe]

I am unable to get a picture to post despite several attempts. I can send an attachment via email though. Or perhaps I could get some pointers about posting pictures. Sorry.
Bruce Rowe

[bfrowe]

I was able to post a picture to Lorsails' web site and Doug responded with the following: "your hulls don't have enough volume or rocker". My problem is trying to reduce pitch and yaw in light to medium air and some chop. I can get out of the stern and into the center of the boat to help reduce pitching, but there is considerable rocking about from the wave action on the amas. How would more volume address that?
Bruce

[Doug Lord]

Bruce, added volume would allow the boat to develop more righting moment before the amas were pressed down too far. But I'm not sure that is appropriate for your boat having never sailed it. I can say that IF you do add volume or keep the same volume and add beam that you should get the help of an NA/engineer to make sure everything is strong enough.
The most important thing I noticed from your picture was the straight deck with minimum rocker to the amas. On my 20' tri I used 16 foot amas that had a shape similar to a Hobie cat except symetrical and they handled rough water at relatively high speed really well. I think amas similar to that but perhaps smaller-about half way between what you have now and a Hobie 16 hull might work well on your boat.I don't think you want to even consider flying the main hull on that boat so the amas will always act as a sort of "power limiter" in that when they are pressed too hard they'll submerge.
I think a somewhat bigger ama as I suggested above with perhaps more beam as well would dampen the "rocking" you mentioned-if I understand you correctly.
In building a small powerfull under 20' "mini MAX tri I would NOT use the type of ama I'm suggesting for you; in that case I'm using a variable geometry ama that will have lower wetted surface(or no wetted surface) in light air and that will plane in stronger winds with the main hull flying. Hydrofoils will aid pitch stability and the crew's weight will provide righting moment and some pitch stability. A whole different animal from your boat...

[bfrowe]

Doug,
Suppose I eliminate the ama entirely, to be replaced by a foil that would mimic the lift of the ama. In light air it probably would not touch the surface. I would lose the righting moment provided by the weight, but I could either move myself outboard or reduce sail area.

[Doug Lord]

Bruce, a number of boats have used foils to augment stability. You could possibly use a angled foil(Bruce foil-I think) on each side-only one immersed at a time that would add righting moment AND take the place of the leeboard. Look up the Slatts 21 and there was a wild 60 or so footer in the UK that used the same concept.Also, Hydroptere uses such a concept(surface piercing foils) to lift the whole boat.The angled foil like a Bruce foil or surface piercing foil is prone to ventilation; a better system might be some form of retractable fully submerged foil and fin...
I'm not sure your boat would be fast enough to make good use of any foil combination for righting moment. Any idea how fast your boat is in a 10mph wind?
==============================
Check this site for some info on Bruce foils; scroll down for definition a little history and an illustration:
http://www.schachtdesign.com/proafile/primer.html

[bfrowe]

Upwind: 5 kts or so
Downwind: 5-6 kts

[bfrowe]

Now that's an exciting website! Ironic name for a possible ama improvement. It might work especially well for my application because the center hull section is just an ordinary Sea Pearl monohull. The amas were added to make a more stable platform for pleasing heel averse wives and less athletic sailors. Maybe I could have two seperate systems: ama style for swimming and socializing and foil style for zooming. But, sounds too good to be true-what's the catch?

[Richard Petersen]

The answer to the opening question is in 80% of the answers.

[fhrussell]

Hello Group Members,

For the handful of people looking for the plans for an 18' Malibu Outigger; they can be acquired by sending a $50.00 check (USD), payable to “Malibu Yacht Club” to:

John Abel
20494 Royalstone Drive
Malibu, CA 90265

And for all you enthusiasts, Wayne Mort has original drawings by Warren Seaman for a 25 foot version. Let me know if you are interested and I can try to get those copied either by Wayne or Warren for a nominal fee. There are no plans available for the 12 foot version.

Aloha,
Frank

[Doug Lord]

Bruce, judging from afar based on your info I'd say forget the foil and stick with some sort of ama. Your boat does not appear to be fast enough to make use of the foil too effectively .

[mattotoole]

With the obvious exception of the Rave and the Trifoiler,
the small trimarans I see on the web are too low on the water and this is so much in contrast with the spydery look of the big racing trimarans. The small ones dont trasmit the impression of agility and nimbleness that their bigger brothers suggest. May be that's the reason for their scarce appeal. Anyway they are a good platform for testing hydrofoils. They are easily and cheaply built in plywood, sharpie style, and lend themselves perfectly to workboat use.
Marco

Appearance is one thing, but I agree, being close to the water may limit these boats' appeal. One of the advantages of a small tri is that it requires less athleticism -- a skipper can sit in one spot and hardly move. But people seeking that probably don't want to be getting doused by waves and blasted with spray.

This was one great thing about the original Farrier Trailertri -- it was relatively dry, more like a Rhodes 19, etc., than anything with similar speed. Even the Tremolino was a wet boat.

[Doug Lord]

I think small tri's designed to fly the main hull like the Open 60's would be a lot drier and a lot faster than most current small tri's and maybe some cats as well. I think the tri platform is ideal for a non athletic approach to high speed sailing BUT it doesn't have to be that way. The power added by moving the crew side to side on a "square" under 20' tri would be awesome...

[WFSTANTON]

I Would Like To See A Plan For A Small Tri Based On The Hobie 14 Hulls For Amas And The Rig On A Home Built Center Hull. Hard Seats Outboard The Gunwales For Stability And A Centerboard For Easy Beaching. Sporting Performance, And Pleasure, Combined With Simplicity And Utility. Yoohoo Anybody Out There Listening? :)

[mattotoole]

I Would Like To See A Plan For A Small Tri Based On The Hobie 14 Hulls For Amas And The Rig On A Home Built Center Hull. Hard Seats Outboard The Gunwales For Stability And A Centerboard For Easy Beaching. Sporting Performance, And Pleasure, Combined With Simplicity And Utility. Yoohoo Anybody Out There Listening? :)

Well, there's always the Tremolino, based on Hobie 16 hulls. While most were fiberglass, the original design was for home-built plywood. I'm sure the plans are still available.

Hobie 14 hulls probably don't have enough bouyancy for a tri like you describe -- in fact they have trouble holding up two people in heavy winds.

The problem with boats like this is, the rig and hulls were never engineered for the trimaran's greater righting moment. Evrything's overstressed, and tends to wear out or break. Tremolinos are fun boats within their limits, but tend to suffer from blown out sails, etc. Many Tremolino owners have replaced the original Hobie rig and amas with more suitable parts. Of course old Hobie parts are plentiful and cheap, which is probably the appeal.

The top choice in this category would be the Haines Hunter Tramp, the original Farrier-designed folding tri daysailor. It's exactly what you seem to want. Of course availability depends on where you are. I'm sure there are plenty in Australia. I've seen several in the US over the years. I don't know if they were ever officially imported, to the US, or Europe/UK.

[Doug Lord]

Matt, I searched for this boat but came up blank, Do you have a pix or link that you could post?
---------------------
WFStanton, you might look for the 18' Sailbird tri-don't know anything much about it except that it was not a real high performance design .I think it was built in or around St, Pete....

[mattotoole]

Matt, I searched for this boat but came up blank, Do you have a pix or link that you could post?


Doug, I'll try to find some. I've actually come across articles about it recently, but lost the links. In the meantime you could try searching for stuff about the designer, Ian Farrier.

[mattotoole]

OK Doug, here you go:

http://www.f-boat.com/pages/trimarans/Tramp.html

http://www.f-boat.com/owners/

Here's one for sale, assuming this isn't an old web page:

http://foma.sailnet.com/classifd.htm

[Doug Lord]

Thanks , Matt!

[SeaDrive]

see:
http://www.geocities.com/tremsetters/
especially:
http://www.geocities.com/tremsetters/tremplans.htm

[bfrowe]

Look in Small Craft Advisor: May/June 2002 issue #15 for a cover picture and boat review of Haines Hunter Tramp.