I found the same control problems with a drill and sanding disk -- too easy to run away on you. I took my seat in to work (ahem) and carved it using a large belt sander. Not hand-held, but a large one mounted on a stand, and I moved the seat back and forth over it. I think a smaller mounted belt-sander would work just as well. The sander also came in handy for making the bottom of the seat curved to fit the kayak. I made a cardboard template of the hull bottom in that area and used it to make a curve on the front and rear, then sanding down to the curves. The belt sander works well for roughing work, but hand-sanding afterward is necessary to smooth it out well.

You might think about making the seat part first, then shaving the bottom until you get to the desired 1/2" thickness. I didn't check the thickness with anything but my fingers to make sure I didn't sand through, but how about just poking a pin in it every so often to check the depth?

I made a drainage cut in the bottom of mine, too -- just a V-shaped cut-out done with a utility knife.

I glued the seat down with only a blotch of conact cement at each corner, and it's held up great. I didn't want to cement it down too completely in case I decided to move it later. Same with my Pygmy-purchased Minicel foam knee braces -- I only put a strip of contact cement down the long edges, and they've stayed on, even though they get pushed on sideways by my hand when I carry my yak on my shoulder.

As to sharkskin -- did you ever make candleholders out of tin cans in scouts? By perforating the metal with a hammered nail you get a small hole and can make patterns around the can. On the inside the metal forms little barbs around the holes. Imagine a whole mess of those holes perforated in very thin metal and you have sharkskin. Here's another similar thing, and boy is this one obscure : have you ever seen a pie-cooling cabinet at an antique store? The sides and doors are made of perforated, galvanized sheet metal -- an early form of screening to keep the flies away...

Dean
(or should I say Cliff Claven?)

: Does anyone have suggestions for tools to use shaping a foam seat?
: I've started using an angle grinder with 50 grit disc,but I can see it will
: get tough to control as I get deeper.
: Can anyone post a pic or description of sharkskin?

: To indicate when I've got down to 1/2" I plan to put 2 saw cuts on the
: bottom of the seat from the back to the middle. I hope this will work?
: should also provide drainage.

: TIA Terry