: its interesting that you bring that up.A friend and I were discusing the cat
: idea and we think a cat would be easier than two boats.All you have to do
: is build two pontoons you could leave the forms inside for more support
: and something to anchor to. first boat 500 - 700 US$$$

Maybe much less than that for the hulls. You wod have to add on the cost of a sail rig.

My neighbor just bought a used Hobie cat, and hs been refinishing it on his front driveway. It has given me the opportunity to get a good look at the parts.

The hulls (or pontoons) for a catamaran are much simpler in design and construction than hulls for canoes or kayaks. Forget rocker, initial stability, secondary stability, swedeform vs. fish form, and round vs. hard chine designs. The pontoons are essentially straight with the same cross section over most of the length. They taper a bit at the ends. The cross section is basically a "V" shape. On a kayak this would mean lousy stability, but when you have TWO of these shapes supporting your boat there is great stability, and little water resistance.

the deep "v" shape is conducive to building with plywood. You can build an internal frame of plywood bulkheads or ribs supporting full length chines and use that to support your plywood parts, or you can use stitch and glue techniques. Since you are building two of these, you can save time by stacking your materials and cutting two copies of each piece at the same time.

If you use the internal frame, you can just screw and glue your plywood to the chines. With reasonable care this type of construction can be made water tight and simply painted. Or, you can cover the seams with a single layer of fiberglass tape embedded in either polyester or epoxy resin.

Basically, you can rip a sheet of 1/4 inch plywood into 3 strips, 8 feet long, and assemble these to make a triangle for your pontoons. So, two sheets of plywood give you a 16 foot long pontoon, and 4 sheets give you two pontoons. With lauan plywood selling for under $10 US a sheet, your basic materials start at $40. Add on two more sheets of 1/2 inch plywood for the bulkheads and rip some 1 x 1 chines from some pine boards and you'll probably be close to $100.

(I'd rip the plywood into two strips that were each 17 inches wide. One would serve as the left side of the pontoon and the other as the right side. The remaining piece would be a bit under 14 inches wide. I'd trim this to about 13-1/2 inches wide and use it for the top of the pontoon. Mid frames for the pontoons would be triangles of 1/2 inch plywood.)

Add on the glue, fasteners, paint, epoxy and glass tape. Depending on what incidental materials you already have, you might increase the cost by anywhere from nothing to another $200. Total for the two pontoons should be well under $300 though.

You can tie the two pontoons together with nothing fancier than a pair of 2 x 4's and some bronze bolts. Or you can get more elaborate.

Since the pontoons are basically tringles, you can multiply their area by the length, and figure the volume at any particular depth. If you calculate this in cubic feet, then multiply by 60 to get an idea of how much flotation each pontoon will provide. Since you have two pontoons, double that amount for the carrying capacity of the boat. Roughly doing the math in my head, I'd figure that with 12 inches of the pontoon submerged, (and about 4 inches above the water) a 16 foot long pontoon would support about 800 pounds, and two of them would carry 1600 pounds. With two people on board and some gear you should float a lot higher, and have plenty of reserve bouyancy.

Some people fill their pontoons with foam so they maintain the flotation even if the pontoon is ruptured. this is expensive and adds some weight. Personally, I'd find some foam packing materials and stuff as much as I could into the otherwise hollow pontoons. Should the pontoons leak, the foam materials would displace a significant amount of the water and keep the boat afloat. the loose nature of the packing materials would allow the water to eventually drain out of the pontoons.

Hope this helps.

PGJ