You can never have enough clamps, especially when building a boat.
Here's Platt Monfort's method of making your own from plastic pipe.

Step 1: Get a Big Pipe and Cut a Bunch of Rings

Any plastic pipe will work. This is black ABS. Polypro would be nice. Never use PVC for anything. Get the size and thickness of pipe to match your clamping needs. Cut the rings wide enough to give you the clamping force you need and so you can spread the clamp with your hands.

Step 2: Cut Through the Ring in One Place

Use whatever kind of saw you like.

Step 3: Make a Big Chain, Wear It, Goof Off.

Link all your springy clamps together and go around wailing "I forged it link... By... Link...."

Step 4: Get More Force With Rubberbands

To use it, just spread the jaws and clamp it onto your workpiece. To get more force, wrap some rubberbands around it. That's a bright idea from Numberandom

Step 5: Clamp Happy

You'll never run out of clamps again! Even a cockpit coaming is easy. That's a "Pax 20" kayak kit from CLC boats.

Step 6: The Finished Thing

You'd never guess what would come from under that forest of clamps.
A few hours after gluing, the clamps come off, and after a little sanding and a coat of epoxy,
here's the finished cockpit ring. Oohh! Ahhh!