Designing a performance small trimaran

Small Tri

Hi Doug, there will be a point in the wind range when the tri will start to outdo the Moth in straight velocity. No one could possibly calculate where that point is, as the variables are far too many, and we don't have sufficient knowledge yet. I am convinced that a planing tri with much larger sails, would have a better top speed than a foiler Moth, but I would bet that in a series of races between the best small tri that you or I could come up with, and a top foiler Moth, the Moth would win easily. I can't see the point now of trying to develop this particular argument further, as I can't add anything more than I have already, and you would be in the realm of sheer speculation.

 

Maxi mini Tri

To me it is exciting to contemplate a small tri that utilizes the same or nearly the same attributes of power and speed used by the ORMA 60's. At least square,possibly "foil assist", possibly newer technologies like the ROH concept or just a planing ama with foil lift at lower speeds. In a small platform all this could be tried separately or together for a bit less than
a gadzillion dollars. As I've said before I'm amazed it hasn't been except to a very small extent in the trifoiler and Rave- neither of which is fast in light air. A mini Maxi tri could be really fast across the wind
range with potentially exceptional speeds especially in 3-20 knots.
Now , if only someone would build one so I don't have to...

 

Small Tri Realities

There's a common perception that because trimarans look like higher tech machines coupled with the fact that they are typically equipped with more performence oriented rigs, that they should be classified in the tech solution end of the sailing design spectrum.

I don't happen to necessarily agree with that approach and I design them, build the prototypes of my designs and sail them with regularity. I use my boats in all sorts of wildy varying conditions from mountain lakes, large rivers and ocean coastal cruising in a wide latitude of wind and water conditions.

I have designed tris that are decidedly high tech in nature and I've also done a few of them that are low tech, retro solutions to a pleasant multihull experience.

All of them are fun and it has little to do with the technology that is employed to get you to that point out on the water. Yes, it's possible to design and build a really fast trimaran in the sub-20' range, but it's going to cost you money, use potential and time to get there. A boat that has most of the speed of the hotrod version, with way more overall serviceability, is going to be available for a lot less cash, it will be easier to build and it will be easier to get parts, wherever you may go with the boat.

There are distinct vanishing limits for go-fast boats of this type under 20'. Mostly that is a function of the absolute weight of the intended crew and the ability of the sail plan to propel you and the boat as fast as you may wish to go. The human scale issue crops-up again when you want to consider comfort issues aboard the craft. A sub-20 rocket ship will not have much in the way of creature comforts at all due to weight considerations, windage issues and everything that goes into that envelope in a design sense.

If you are firmly limited to the 9' 6" beam figure, and a demountable or folding system is out of the question due to complexity... then my suggestion is to build a fast cat or hang with the proa. If you can build in the demountable or folding mode, then a whole bunch of possibilites open-up for you with regards to base design potential.

Perosnally, I'd stick with the more doable issues of a straight forward trimaran with a vaka hull mounted board of your choosing and at least 150% amas for full spectrum sailing potential in a really wide array of conditions and crew weights. I'd forego the whole, lifting foil, thing until you get the base boat and all the various sailing issues sorted correctly for the type of sailing you will likely do. There are literally dozens of design and structural issues to deal with that do not appear in the design brief for a more conventional trimaran design, once you decide to put lifting foils in the amas and/or the rudder.

Sure, you can do it and you'll need to dedicate plenty of time to the tedious task of sorting the various relationships in order to get it to work correctly. It can be done, no question about that, but it will cost you in lots of ways to get there. That approach is not a budget conscious path. From my perspective, that sorting process is time that is not available for the pure, uncluttered pleasure of sailing. Of course, it's your choice as to how to proceed.

I'd be happy to help you out with a group of simple folding schemes that could get you into a wider beamed boat while still meeting your storage issues. I can also help you with material suggestions that will give you a few shortcuts to a finished boat with excellent performance potential. If that sort of stuff interests you, just write me off-list and we can exchange ideas.

Chris Ostlind
Lunada Design

 

Cross beams PVc/Stainless pipe / bamboo inside PVC

Frosh, If we are building sm. Trimarans for flatter Sea day sailing; and want cheap and lbut good performance- For the outriggers - what about using PVC outside with stainless pipe inside- small amount of fiber spacer inside- Two sections- one straight across & one bended in from across cabin top? And have you considerd long pieces of bamboo -maye 1 to 2 inch widths- like stringers, epoxy inside also? Or some combo of the above? From Peter in Bali