Small trimarans under 20'

90 lbs includes main hull, cross bars, amas, mast, trampoline bench, rudder, and centerboard. I may reverse engineer a similar lighter rudder assembly, but that's the general size of the rudder and same balance.

I just took a more overall look at the design plan on the tri, and then at some maxi trimarans. I agree, it does look like they would all have some rather bad weather helm. Especially the maxis. The daggerboards are canted aft but still infront of the mast! Here's a perfect example of three of them... Looks like they would all have bad weather helm, why are they that way? Is it ok to copy them?



Edit: I suspect it has to do with the fact that the sail rig is in the middle of the boat and it's designed to sail with the majority of the weight supported by the ama, so in a sense, the actual sail rig is 30-40 feet to windward of the boat. Mod 70s have it just in front of the mast. Same with the multi 50. The Diam 24, on the other hand, is behind the mast... Perhaps on these smaller boats it's better to have it more traditionally balanced... I could move the mast step 2 feet forward back to its original(pre-refit) position, or move the daggerboard aft to right behind where the mast is now, or both. I'll play with it later.

What is you all's take on that?

 

In fact, owing to the big rake of their daggerboard, the CLR is more under the mast than before.The explanation could be their very large beam and the big lee-helm associated with the drag of the lee outrigger. to compensate you can move the CLR before the aero center of effort. On My Tremolino the daggerboard was too far behind the mast and I had a big lee helm. On my Strike 15, the daggerboard is 2 feet behind the mast and the equilibrium is quite good. My strike 15 is 3.50 m beam.
Cheers

Patrick

 

I see. Sounds like it would be wise to go toward the route of the Diam 24 and Strike 15, at least on these small craft. I looked at sizzors and the Mosquito trimaran. Sizzors has a single daggerboard about even with the trampoline. The Mosquito has twin daggerboards also behind the mast. I'll probably plan to move the mast forward back to it's current step(2 feet in front of the forward crossbeam) and maybe keep the centerboard for now until I am sure I want to change it. I just don't like the extra drag of the large centerboard box hole on the bottom.

Thanks for your input guys, this is why it's important to have other people look at things and point out where a design is way off.

 

Here's the latest model with a few changes. The mast is moved forward, and the centerboard is shown in it's current configuration. I also moved the lifting foils on the amas forward about 9 inches. The jib got bigger because I would be sheeting it to the front crossbar, but I don't have a place for the spinnaker. Thoughts? Bowsprit?

 

Self tacking jib, move the ama foils even further foward, bowsprit with screacher and job done, but still think your weights are way out of line, are you sure you are not quoting kilos. The rig and sails alone are going to be over 50lbs.

 

I would put also the daggerboard somewhat aft : it is better looking and performing to correct unbalance with aft mast rake than forward. I also don't understand the weight,
my Strike 15 is 128 kg, using carbon beams, carbon mast and rudder, vectran waterstays. But I can trapeze and likely it will not break with two people on board and 20 kt of wind.
Cheers
Patrick

 

Ok, for the weight... I am quoting US pounds... It's skin on frame guys... That's all. This 15 foot canoe weighs 26 pounds. Completed, without cushion or paddles.



Skin boats are very light. The main hull on the trimaran as it is now only weighs about 40 pounds, WITH the centerboard and rudder assembly. The whole trimaran as it is now weighs about 100 lbs. A good chunk of that weight is just the crossbeams and mast(about 20 lbs). Each ama(as they are) is about 5 lbs each. New amas will probably be at least 15, maybe 25 depending on how light I can make the foil trunks.



I'm aiming for 30 lbs on the mast, and the sails are fairly light as well. I'm more worried about crossbar weight...

 

That's a nice approach, the skin on frame is amazingly light.

Scarey. But nice.

Might look at whether hanging the foils onto the front crossbeam could relieve the weight concerns from adding cases to the amas.

More pictures!

Cheers,
TomH

 

OK, I understand, It is not what one use to call a trimaran but an outrigger canoe. A huge difference in design loads and use. Also the rig shown in the photo would blow up if you had the same righting moment as a regular trimaran ! I also built a stich and glue canoe (a wonderful little kate) at 22 lbs ! DIY Tris are wonderful to use in flat water sit in the mainhull but will dismantle if you use them as regular Tris in a medium breeze(for example you put a crew to windward or on trapeze). They are designed for a low righting moment.
I wait to see your boat sailing in breeze and waves.
We had to compare weight of similar sailboats !
Best wishes

Patrick
Cheers

 

RC, I hope you made substantial ring frames below the beams, especially the forward one, because there will be some decent twisting loads from the rig there and even more if you put foils in the floats.
However with the ultra light boat you have, you're not going to require a large sail area to move it - so with the rig shown, will be fine in drifting conditions but too much in a breeze. Will be very interested to hear your sailing results. Because lightweight is the magic word for multihulls ... as long as the craft hangs together.

 

If the heeling force of the rig is countered by a lifting foil, the crossbar that transfers this leverage can't be certainly flimsy
Shape can help redirecting the forces: Newick trimarans are a good example.
Water-stays will help too.

 

She handles the rough water alright, but she's dead slow. She can barely keep up with 25 foot cruisers. Most of that is due to the sail rig. I think what I'll do for now is beef up the crossbars for more width and ability to sit out away from the center hull, and do the new mast, then deal with amas later. The whole idea is to sail with the first reef if the wind picks up.

I hesitate to call it an outrigger canoe, but you could call it that. In any case, the design keeps moving more and more toward Randy Smyth's Sizzors trimaran. Scary light and fast in drifting conditions, which is where I spend 85% of my sailing anyway.

 

randy Smith use a lengthened A class cat mainhull, Shortened A class cat rig with jib (like my Strike 15), carbon tube beams and waterstays. Everything correctly sized weight hts weight !

 

Sorry, Randy, weight its weight !

 

Sizzors is a great example of a fast boat for light wind but I think you are missing how it works. It's not so much a trimaran as a monohull with training wheels. The amas are never intended to displace much water they are just the best way to terminate extreme hiking wings. Righting is primarily from ballast shifting (the crew) not from shifting buoyancy out to the ama. You can do the same easily by just raising the amas on you boat. New amas don't help because they should be out of the water anyway. The last consideration is that Randy Smyth is very talented in sail handling and light wind is usually highly variable -which will make balancing much more difficult for you. Your result will likely be moments of brilliant performance in hours of dull frustration.