Larry,

There are a number of different size cockpits out there. Also similar sizes with different shapes.

I think the important thing is for you to find a cockpit size you are comfortable with - big enough that you can get in and out without a hassle, but small enough where you have a place to install knee pads, thigh braces, etc.

My advice would be to find a cockpit you like, and copy the dimensions. If it is on a manufactured boat, the boat's manufacturer will have a spray skirt that fits it.

It's probably not as big a deal as it appears. A friend's whitewater boat has a noticeably smaller cockpit than his sea kayak, but he has used the neoprene skirt from the sea kayak on his whitewater boat without a problem. So spray skirts do allow for some deviations.

Good luck,

Ken