I had the same experience with an angle grinder. They run at 10,000-12,000 rpm and are hard to control.

I recently bought a Makita GV5000 sander for another application, and found that it works well for seats. It also does a dynamite job on the underside of decks and inside hulls, fast, light, and controllable. Uses 5" disks, weighs 2.6 lbs., and runs at no-load speed of 4500 rpm. Much easier to control than a drill, because the handle is closer to the business end. Looks like the same tool Vaclav recommends on oneoceankayaks.com for sanding insides.

: 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