Consider also BearboatSP (Google it). It is free kayak design software. I have designed and built my last 4 kayaks using this software. For the last two, I have downloaded the data from that program into Rhino which on the Mac is now in Beta and can be used for free at the moment if you accept their rules. Within Rhino I have created all the deck details, hatches etc. and then have passed that model on to computer milling machines. Rhino is not easy to learn IMO but in part that is because all 3D software is difficult. It is a marvelous tool.