The basics….
This boat will a catamaran first. The hulls will be 10 inches deep, ten inches wide, and 18 feet long. The hull sides will be 5 inches deep and then the bottom will be a semi-circle. The flat top and sides will be made of 3 or 4 mil marine plywood and the rounded bottom will be stripped with ¼ by ¾ cedar strips. The hulls will have 5 inches of rocker and be symmetrical on the bow and stern. There will be Meranti plywood bulkheads every foot and these will have a large part of the material removed to save weight. There will also be a backbone running the full length made of either Meranti of marine plywood and it will also have much of the center material removed. I will put extra blocks in two places on each hull where the deck fixtures will be mounted, and where the rudder attachment points are.
The surfaces on the inside will all receive a coat of resin and the outside may get a layer of cloth as well. This boat will be used mostly in the ocean and needs to be able to withstand a careful drag up the beach.
The hulls will be spaced 6 feet center to center and the mounting frame will be made out of aluminum with two attachment points per hull. Not sure on the attaching details yet…..There will be a rudder fixture on each hull but in the cat configuration I would expect to use just one in most conditions. I may find that having the rudder attached to the main frame is better, but I don’t know at this point. It may also not be necessary to have the rudder in the water at all times.
The cat will be set up initially for one rider but the eventual goal is to have a tandem. The rider will sit in the middle of the frame on a seat similar to that on a recumbent bike.
The drive mechanism will consist of a bicycle bottom bracket mounting a bike crank and sprocket, a bike chain running forward to a smaller sprocket modified to drive the input shaft on a 90 angle gear drive. There will be a shaft running from the output to the rear of the boat where a propeller will be mounted. I am not sure at this point what the shaft and propeller configuration will be but……….This will be the same type of drive system that will be used on the single boats as well. Eventually I would like to switch to something more like the
Seacycle Drive
on the tandem but have the riders one behind the other instead of side by side.
Step 1
The first step now is to lay out the pattern for the hulls. They will be constructed upside down with the deck added last. I am laying out 19 feet of plywood 16 inches wide which will be supported in numerous places by cross strips of the same material. My basement floor is quite level but I will trim the pattern using a laser level. Then I will use a snap line to lay out three straight parallel lines for the full length. The center 8 feet of the hull has a constant profile and both ends have the same taper for 5 feet each. I did a test previously to see how the strips would work so I will use the curves from that to lay out the profile on the plywood. I have aluminum angle pieces to screw into the plywood to hold the sides in position while I install the rest of the frame. Once I have the pattern drawn out on the plywood I can cut and join (scarf probably ) the pieces for the sides and backbone.
