I need advice

Hi
I am a French student in the "Ecole Superieur du Bois" in Nantes (France), it's a High School which trains engineers for the industry of wood. I am very interested in wooden boat building.
This year I have decided to lead a project which consists in designing a litle catamarn (about 5m)
I need some adice about the way of building the hull as I would like to have a fast building method

Yours faithfully

[tspeer]

Take a look at Kurt Hughes' Cylinder Mold Method (http://www.multihulldesigns.com/). It's perfect for quick, low cost multihull construction. He also has plans for small trimarans - you may be able to adapt them to make a catamaran.

Better yet, buy a used catamaran and build new hulls for it. That way you get the mast, sails, beams, hardware, and foils for less than you'd pay for them separately. And you don't have to expend any effort building the parts of the boat that are of no interest to your studies.

[yipster]

Kurt Hughes' Cylinder Mold Method is interesting, just did not completely got the stem system idea. Also it limits in shape, its a fine shape, but cant see how to use it in forexample the more atractive lightbulb form. The quest is for a fast building method wooden boatbuilding project so i think hard chine plywood may be better suited here? Guess the cilinder mold method can also be used for laminating wood.

[tspeer]

jb is interested in making hulls for a beach cat. That means he's interested in hulls with a length/beam > 10 and pretty much straight (or somewhat flared) topsides. He also specified fast building in wood.

Those spec's are traditionally met by the tortured ply method, where you cut out the sides, stitch them together at the bottom, spread them apart at the deadrise angle and glue/tape/fill the center seam, then force the topsides into a form to shape the rest of the hull. The drawback of tortured ply is that you can only form hulls that have no more curvature than you can force into the ply, and it's difficult to control just what the shape is.

The cylinder mold process improves on this by starting with plywood that is already formed in curve instead of a flat sheet. The cylinder mold is fast to build because all the stations are the same shape and the veneers are stiff enough not to need a lot of battens in between the forms. So for a little extra effort, you get a big increase in the family of shapes you can create.

Once the sides are molded and cut, the rest of the hull building process is the same as for tortured ply (steps 4 and above). The torture process will induce different curvature and compound curvature into the hull contours. There is still some uncertainty about the actual hull form, and that's why it's useful to start with established plans. The Gougeon book on boat building has a chapter devoted to the tortured ply method, including suggestions for making subscale models to see how the sides will fold up. Their modeling process would probably work for cylinder mold, too, if jb wants to design a custom hull.

The sides come together at the stem when they are forced into the deck-level form. Then they get glued and taped to form the bow. A larger hull would probably have a stem piece glued between the side skins.

Hard chine construction introduces its own limitations because each facet is a developable surface, or close to it. Minimum wetted area is important to a sailing catamarn, so round bilged hulls are the norm. That's the real attraction of CM over tortured ply.

[flame]

A good source to modern wooden boat construction, including a special section on catamaran construction using sheets of plywood can be found in

The Gougeon Brothers on Boat Construction
ISBN 0-87812-166-8: english
ISBN 3-926308-00-1: german (Title: Moderner Holzbootbau)

If you are going deeper into wooden (sail) boats, this is a MUST in your bookshelf

Cheers
Mike