Catbox Plans

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In recent years I've seen several PDR boats at our Rend Lake meets. Chuck Leinweber asked me to design one too but I guess I put it off thinking there was already a lot of variety. But enough arm twisting did the job and I ended up drawing Catbox.

The basic idea for the PDR class is pretty sound I think. The bottom of the boat is tightly controlled with variations of just 1" allowed, but I take that to be a "builder's tolerance" sort of thing and not a designer's tolerance. I took the shape shown right from the Wikipedia article on the PDRs so it must be true. Hull depth can be varied a bit. At the start I got fancy and tried to give it an elegant sheer but that never works for me. Whenever I try hard for elegant I always end up with ugly so I went back to a straight line which is I think what this class is all about.

I made it with an air box on each side. These serve many purposes. In a knockdown this boat should come up more or less empty of water because the side boxes are deep enough to float all high and dry. The inner wall of the box strengthens the bottom and that combined with the arc of the bottom should negate any need of added bottom stiffening even though the bottom is just 1/4" plywood. The wall also supports the decks which serve as seats. And if you put big deck hatches in them you can store your gear in the boxes and it should stay dry. Boxes like these need to be left open to the air anyway when not sailing to keep them from rotting. Very important.

I did a lot of things with Catbox that I don't usually do. No external chine logs and no bottom stiffeners. I'm keeping the thing smooth as can be since this is a racing boat! I guess you could try it with external chines logs if you wish but I see no advantage here. The external sides and inner walls are all the same but don't forget you will need two righties and two lefties.

For the rig I took a Sunfish rig, at least I think I'm using the same dimensions. Catbox is a lot shorter than the Sunfish but it is also a wider so I don't think it will be overcanvased in general. The Sunfish sails are available new here and there but if I had one of these I would try polytarp first, very cheap and appropriate here and to my mind if properly done polytarp may have an edge over sailcloth in light winds.

Let's see ... NO LEEBOARD! It is true. I didn't want to spoil a sleek racer with a leeboard so I gave it a daggerboard. It is attached to one of the inner walls, not in the middle and in the way. The hull/daggerboard interface should have less drag than a leeboard rig. I also arranged the board case such that the angle of the board can be changed - swept forward or aft to change sail trim. Should be a good speed trick in the right hands under the right conditions. Anyway, it will be something interesting to tinker with.

That's about it. Simple nail and glue construction needing four sheets of 1/4" plywood for all.


I recommend strongly that builders buy Jim's book with the Catbox plans as it helps a lot.
Mike John

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