http://www.seilas.no/photoalbum/view/?size=medium&id=125301
http://www.seilas.no/photoalbum/view/?size=medium&id=125297


I have no more information unfortunately, but it looks like the rig can slide from side to side. Cool boat!

It looks cool, what would the advantage of the rig sliding, other than being a good way to cut off fingers?

Uhm.

Added righting moment.


Alot of rightning moment.

Found the builders homepage: http://www.asterwind.com/ but it is in french..

If improved righting moment is the intend then he is sliding it in the wrong direction. You'll want the rig on the luff hull then !

Wouter

Indeed.

could you get a hull out of the water that way?

There are, at least, two sides to every story.

http://www.planet.fi/~kcad/cpc/Cruising_proa_concepts.htm


There is also this. I have a set of these plans and may build it someday.
http://www.clcboats.com/boats/pacificproa.php

I've seen on of these on a trailer in CT. Always wondered what the heck it was.

Not the best looking craft, especially on a trailer.

In reference to the CLC design above, it looks like you could easily add another Ama to the other side and have a very neet little trimaran. I wonder if they could do a kit for the wood Blade F16? Most of their stuff is built using the Stitch and glue method while the Blade is done by the tortured ply method, I wonder which is lighter and which is stronger. Any thoughts out there? Maybe they could even do some A cat hulls for homebuilders?

"tortured ply" method is a more developped form of the general "stitch and glue" building method.

In effect the first uses "stitch and glue" as well but adds steaming to the proced in order to end up with a more (complex) curved surfaces.



Hard to say, dependents on the specific design.

Wouter

The pacific proa is a different concept, on each turn the bow becomes the stern (and viceversa..). In this case it´s the mast that is moved sideways.

The site doesn´t explain anything. It just says that it´s a catamaran 30% faster and that the design is done to improve stability and, more importantly, to avoid turtling.

"Le bateau est équipé de notre technologie GRL qui permet de déplacer le mât d'une coque à l'autre.
Cela lui permet d'éviter de chavirer et surtout l'empêche de se retourner."

Wouter, et. al.,

If the hulls are of equal weight, unlike a proa, then if you put the mast on the leeward hull, you have the righting moment of nearly the whole boat's weight, but inversely, if it's on the windward hull, a much smaller righting moment, but a much larger displacement moment of the leeward hull.

I've always had a novel (I think) solution as well, but don't want to post it here. (the idea).

If you or another builer type could e-mail me, there could possibly be a patent in it.

In either case, the leeward hull acts as the "fulcrum".

So, if you put the rig on the leeward side, you get the righting moment of the weight of the boat + weight of the crew.


If you put the rig on the windward side, you get the righting moment of the weight of the boat + weight of crew + weight of rig.

sm

Not so. You get practically no advantage of weight when you put the rig on the windward hull. The only thing resisting the boat rotating upside down is the amount of buoyancy in the leeward hull. When you do use this to keep the boat upright, you depress the hull more in the water. You will get some minor lifting effect on the windward hull - but it will be small.

Surely this is just phrased badly, Jake. If this were true, there would be no point to trapezing.



Righting moment is determined by the center of bouyancy (CB) for the boat, combined center of gravity (CG) of everything on it, and the distance between the combined CG and CB (moment arm). Moving the mast to windward (towards the right in this diagram) will move the combined CG right, increasing the moment arm, thus increasing the righting moment - same as trapezing (although the mast/rig will have less effect being lighter than the crew).

Why you would want a sliding mast in a practical boat is beyond me. The complexity is surely not worth it. However, ORMA 60 Tris have used mast canting to good advantage.

I contacted them, they said no. It would take too long for them to recoverer their costs.

Timbo, I dont know if you were asking this question because you wanted to build an A cat, but there are lots of ways to homebuild and lots of designs. Lots of build techniques too.

I could probably get the stations for a current A design and you could strip plank or ply. PM me if you are interested.

Bill

Bill,

what would the target weight with ply or strip be?

Agreed. But now look at a similar diagram with the mast on the windward side (and no trapezing) like we were talking about. The large majority of the sail pressure is offset by the buoyancy of the leeward hull, not the boat weight, in that arrangement. There would be very little boat weight on the side of the sail plan that provides the righting moment in your diagram.