Here are some photos and a drawing of some planking nippers I made recently. The drawings are for clamps with a 6 inch throat although I think they could be easily scaled to any desired size. Below is the text I wrote for a friend who was interested in making some for themselves.

Making the Plank Clamp

Materials
12mm (1/2") Baltic Birch Plywood
1/4" x 3/4" Hardwood (I used walnut)
1/4" dowel
5/16 x 5" carriage bolt
5/16 flat washer
5/16 wing nut
1 each of the bolt, washer and wing nut is required for each clamp.

For a dozen or so clamps rip two pieces of plywood 9" wide from a 5'x5'sheet. Rip the plywood so the face grain runs across the short dimension of the piece. Cut a 1-5/8" piece from the end of one of these pieces to use for a template. Set it aside.

After you have these pieces cut, setup the tablesaw to cut the 5/16" dado. The dado should be 5/32" deep. Cut the dado in the piece that will be used for the lower jaw. The fence should be 2-11/16" from the blade. Reset the fence to 2-5/8" and cut the other piece for the top jaw. Then move the fence as needed to widen the dado to 1"

Cut each piece of plywood in half. Actually, for a dozen clamps I needed two pieces 21" long for each half of the clamp.

Glue the two pieces face to face so the dados you cut form mortises. For the lower jaw, I used a couple of the carriage bolts in the dados as alignment guides. For the upper jaws, I used a couple of scraps cut to fit tightly and waxed the heck out of them. Clamp securely

After the glue is dry, cut the grooves for the hinge. Since the plywood is actually 12mm thick and I didn't feel like working too hard, I set the fence about 1/2" from the blade and ran the boards on edge. Then turned them end for end and ran them again. I increment the fence over a little and repeated the cuts. I did this until the groove was about 1/4" wide. Then I planed the hardwood stock to fit snuggly.

While the glue is drying, make the template. Drill the hinge pivot hole before cutting to shape. I clamped a couple of scraps of wood to the drillpress table to act as a guide for drilling the hole. Leave the guide set up for drilling the jaws.

Cut the template to shape and clean up as needed.

Once the glue has dried, cross cut the plywood into pieces 1-5/8" wide. Drill the pivot holes. Trace the shape of the profile on each blank. I stuck a 1/4" machine screw in the hole of the template to aid in locating the template. A nail driven through an undersized hole in the other end is helpful, too. Just drive the nail so the point comes through the template. Bandsaw just outside the lines.

Using the template as a guide clean up the sawn blanks with a table-mounted router and a flush-trimming bit. The template can be located as before with the machine screw and the nail. I quickly cut a cradle from a scrap of 2x6 to hold the jaw and template for routing the inside curve.

Sand the jaws and break the edges so they aren't sharp. Insert the carriage bolts in the lower jaw aligning the shoulder on the bolt with the hole. Tap the bolt home with a hammer. Add the top jaw, washer and wingnut. Snug up the wingnut to align the jaws.

Cut 1" long pieces of 1/4" dowel. You'll need 24 for a dozen clamps.

(click image above to enlarge)

Although my drawing shows a shaped and drilled piece for the hinge, I ended up making it differently. I clamped the assembled clamp to the bench. Then I spread a little glue in the slot of one of the jaws and inserted the hinge stock. (This piece started out about 48" long.) I let the end of the hinge stock extend just beyond the jaw with the glue. I drilled a 1/4" hole using the hole in the jaw as a guide. The hinge stock was adjusted so there is a slight gap between the hinge and the bottom of the slot on the unglued side before drilling the first hole. A dowel was inserted into each hole as it was drilled. The fit should be tight enough that you won't need glue on the dowels.

Trim the hinge piece close to the clamp. Set that clamp aside. Move on to the next one. Sand the dowels and hinge pieces flush with the clamp jaws. Finish with poly or oil or leave them unfinished.

Here is a shot showing the clamps in use. They are holding the second plank in place on the cradle and these clamps are working out great. I covered the jaws with packing tape to keep from gluing them to the boat.