small trimarans

Thanks Doug.

 

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

 

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

 

Sea Pearl ama's

Can you post a picture of your ama's?

 

Planing amas

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.

 

planing amas

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?

 

Sea Pearl Tri

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

 

Sea Pearl Amas

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

 

volume and rocker

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...

 

SP amas

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.

 

foil/ama

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

 

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

 

Bruce foil

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?

 

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

 

Or a Malibu Outrigger...?

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