If you want to build a boat, have you considered
the Dudley Dix kits built in South Africa? You
could also buy just the plans.

Their Mini design could be built with water ballast
albeit I don't think the kit includes that feature.

http://www.dixdesign.com/didimini.htm

I've thought about building one. I like the mini's but
the wooden designs are not very competitive, albeit
I'm sure they are a blast to sail.

wrote

Thanks Bart:
Knowing a thang er two bout that fiziks an njineerin stuff (MS Physics,
MSEE), I think that water ballast does nothing until it is raised above
the waterline. I'll forego discussion about the diff tween mass and
weight.