Small power trimaran with suspension

[ASM]

As I am focussed on trimarans for their stability, performance and the single engine option (opposed to catamarans) I was wondering if the following idea would be feasable:

What about using a F1 like suspension for the 2 outriggers to 'absorb' some of the waves and to generate just a little extra uplifting force for quicker planning ?

I now there was something with suspended 'legs' on a spider like cat vessel. I also think one needs finetuning of the weights and you would need adjustable suspension since one want just a little force from the springs when the vessel is loaded so you have a uplifting force to help the transition from displacement to planning (see sketch, sorry fo the very rough drawing)

Any comments ?

[rwatson]

Wharram catamarans use rope fastenings to provide a bit of give - but a lot of times I have seen that strategy criticised from both performance and reliability reasons.

In a small trimaran I built, the hull was very thin, and this made the ride very soft and comfortable. It was copying the same principle as wave piercing catamarans.

Generally, hull shapes do most of the dampening. It would be interesting to see if suspension was practical. You may not even need to mess with springs - a flexible arm would probably be less complicated and just as effective.

[Village_Idiot]

Another option would be a single narrow skinny hull with an outrigger (to relieve tenderness). This design will get you the most efficiency.

If doing a trimaran, do it big. Make the outriggers large enough to suspend the main hull well ABOVE the water, then suspend the hull from springs (or torsion arms, as rwatson suggests). That would give you the best ride of all and great visibility, but you would probably need dual engines (one for each outrigger). Granted, this craft would probably be HUGE, but also would be very unique.

[eponodyne]

You could probably start with a couple kayaks as your amas or outer hulls and tie into a third (probably smaller) central hull.

It occurs to me that in all trimarans I've seen, the central hull is the big one; but there's no reason it can't be just big enough to hold the people and the steering controls, and keep the mechanicals and the supplies (if any) in the outer hulls.


Hmmmm.

[ASM]

doing 2 big outriggers means two bigger surface areas, like a cat and then even a small one in the middle, so less efficient ?? furthermore, to keep things simple and inexpensive, I would prefer 1 engine and therefor centre hull needs to hold it at best.

[Trevlyns]

Just a thought here...

A 24 foot proa I designed and am currently building will have the ama (or ouitrigger) pivot from from its centre fore and aft on bungee chord attached from the ends to the main beam. This means it can react differently in waves from the longer main hull and relieve a lot of stress on the beam. Very simple and effective. Might work for a tri as well.

Best!

[Village_Idiot]

Originally Posted by ASM

doing 2 big outriggers means two bigger surface areas, like a cat and then even a small one in the middle, so less efficient ?? furthermore, to keep things simple and inexpensive, I would prefer 1 engine and therefor centre hull needs to hold it at best.

Eponodyne hit upon it. The idea is to keep the center pod as small as possible and out of the water completely, so it is no less efficient than a typical catamaran. Drive-by-wire keeps things simple with the engine controls (more and more outboards are starting to go drive-by-wire). Of course, this doesn't meet your requirements, but I think it makes an interesting exercise in design concepts.

[ASM]

That might sound like a good idea if you wanted to test the dampening effect of spring connected outriggers, though then in actual shape it is a catamaran. I wanted to see if the spring loading, a little bit pushing downwards, would generate just that little more lifting power in combination with a planning centre hull to have planning 'mode' sooner at lower power, thus making it more efficient.

Just the dampening effect is easy, use Sylomer sponge foam (used for floating floors on yachts) on both sides of the connection so it could take up to about 6 mm (or double with double thickness of Sylomer) of movement each way.

Would that soften the ride by the way, or are the physics way different then like a road car's wheels ?

[clmanges]

Here's one way of doing it (the amas, anyway):
http://homepages.paradise.net.nz/garyd/quikama.html

Notice that the attachments allow a little flex, to prevent stress damage.

I like the idea of flexible crossbeams, too.

Curtis

[ASM]

Curtis

Indeed that's a way of having a damping system. I thought about using layered (ply)birchwood as a test , since they have pre-flex if they are arched somewhat, like wooden batts under your matrass.

But still, the question remains, does it help to create just a little extra lift to go in plane sooner ? I know it will be finetuning of weights and springs since you need just that little bit of force on the ama's pointing downwards, one does not want the ama's to be forced into the water too much.

[rwatson]

"It occurs to me that in all trimarans I've seen, the central hull is the big one; but there's no reason it can't be just big enough to hold the people and the steering controls, and keep the mechanicals and the supplies (if any) in the outer hulls"



What you are describing is an early Kelsall Catamaran with its central pod and two larger outer hulls.





http://www.duckflatwoodenboats.com/m...gallery?KID=49

[eponodyne]

Huh, that's sort of what I had in mind when I wrote the post. Mind you, in my head I deleted the big stick and substituted a kite rig; but yes, very much of a muchness there. I guess this is how parallel evolution works?

[ASM]

Not to be a pain in the ..... minds, but does anybody have a clue if it helps to create just a little extra lift to go in plane sooner ? I know it will be finetuning of weights and springs since you need just that little bit of force on the ama's pointing downwards, one does not want the ama's to be forced into the water too much.

[Village_Idiot]

I think any gain in planing ability would be lost due to increased friction of the wetted surface of the amas.

When I think of planing aids, I think of things like trim tabs and hydrofoils. Think small. It doesn't take much hydrofoil to lift a lot of weight in the water, and their small size keeps friction of wetted area to a minimum.

[ASM]

Village

A hydrofoil sounds good but I have zero experience let alone zero knowledge regarding foils. Furthermore, I would like to make it a small fun craft and I fear a hydrofoil would be too complicated for a vessel as a substitute for something like a waterscooter. How deep do these things need to go ? could a single foil at the back (or even at the propnozzle from the outboard) be enough with combination of a little aid from the ama's (so the trimaran becomes a cat on one hydrofoil and two very slim and small ama's ?)

I fell in love with these designs:
http://www.amorousmarine.com/portfolio.php?boatId=15
(8 Hp gas gives 20 knots top speed !)
but have the looks like the:
http://www.amorousmarine.com/portfolio.php?boatId=16