Hello Tim,

Here's a relevant portion of my huge favorite links file.
I didn't check them for a long time but last time I was there they had more than few kayak design sw.

http://www.simtel.net/simtel.net/

this website has many free s/w for download,

cad related, office/business related, & more .

http://boatbuilding.com/cgibin/links/Free_Stuff/Free_Software/

lots of design s/w & plans.

good luck,

Erez