If yer building strip, there's the excellent, also freeware(donate!), Kayak Foundry software by Ross Leidy:
http://www.blueheronkayaks.com/kayak/software/software.htm
He has an excellent user forum on his site, too.

I had the same thought about Sketchup and found it difficult to arrive at what i wanted for SOF frames, fullsize patterns for cutting. I used Adobe illustrator...very easy to enter coordinates, connect points, make bezier curves, etc.
For those who arent fortunate enuf to HAVE illustrator, the free open source clone is called Inkscape.
Available here: http://inkscape.org/ Not a CAD program, it is a 2d vector drawing program....
in other words just what we need to loft.

As to Jeff's excellent point about real ship based software, there is Freeship.
available here:http://sourceforge.net/projects/freeship/
Not user friendly, heres a tutorial: http://www.hapby.v-nam.net/FREEship/FREEship-Tutorial1.html
Plenty more out there.

If yer building strip, there's the excellent, also freeware(donate!), Kayak Foundry software by Ross Leidy:
http://www.blueheronkayaks.com/kayak/software/software.htm
He has an excellent user forum on his site, too.

Of course, a big floor, a flexible batten, and some chalk....

Dave Koslow