The objective here was to design a simple to build, seaworthy hull shape for a double canoe / catamaran. It was hoped to have a shape that would provide plenty of reserve bouyancy and that would not require daggerboards.
The idea evolved as a deep-V canoe hull. About the simplest to describe plausible shape seemed to come to mind like this: set a section of an ellipse as the keel-line, choose an angle between the sides of the hull, and a maximum width for the (sheet plywood) material to be used, and see what one would get. The vehicle for the thought experiment became a java applet.
Below is a screen capture of the screen output of
the simple Java applet that I wrote to compute the lines
for the hull.
The figure shows the cross-sections in black and the profile (at the bottom) and plan (near the top) views in red (at another scale). Several parameters (length, mid-hull depth, bow and stern height, and maximum hull width) are computed and displayed. (For now, you'll have to imagine a water line. I need to add some weight parameters and displacement calculations to the applet.)
The hull is to be made of standard four by eight plywood, using epoxy, fiberglass and stitch and glue techniques. Each side of this 31' hull would be made of four sheets, butt-jointed together. In expansion the sheer line will be a straight line; the edge of the joined sheets. The keel line is an ellipse, and a constant 60 degree angle is maintained between the sides of the hull at each station. The height at the stern and bow follow from the keel, the v-angle, the straight (in expansion layout) sheer, and the width of the material.
In construction several internal frames would stiffen the hulls and divide them into separate compartments. Using two layers of 1/4 inch plywood epoxied together with all butt-seams offset would be stiffer (I think), if heavier and more expensive. Some slight convexity in the sections may be stiffer.
The anticipation would be that the deck rigged on the 'iakos would give space for moving around. The hulls themselves could be decked in several ways. A simple flat deck could connect the sheerlines, providing very little headroom inside. Alternatively, the bow and stern peaks could be joined with a straight line giving a peaked deck on each hull and a bit more (sitting?) headroom near the hull centerline. Better still, a raised cabin could be used in the mid-section of the hull for both space and looks.
The applet may be here,
provided that your browser allows it.
How well would such a shape work for a double-hulled sailing canoe, er... catamaran? Would there be enough lateral resistance to avoid needing keels, skegs, lee-boards? Too much wetted surface? Is there enough displacement in the ends? Would there be hobby-horsing around the mid-section?