Here's a little keel clamp I whipped up for my "Independence" build. The base is 3/4" plywood, and the rest is 1/2" hard maple, but any hardwood would do. I had all the hardware on hand, but if you buy the fancy star knobs etc, the hardware should cost about $20. If you use thumbscrews and wing nuts, you could build the clamp for less than $5.00 plus the cost of the wood.
Download the .pdf below for complete plans and building instructions.
Plans and instruction:
Download the .pdf below for complete plans and building instructions.
Plans and instruction: