also selecting the right abrasive. I jumped when I read 36 grit, not surprised it chewed right in. Even so a light touch with 36 would not ruin anything.

My own technique when sanding/shaping delicate shapes like coaming rims or lawnmower blades or anything plastic is to make numerous light passes and never let the work just sit on the tool. Sort of do a glancing blow, just wiping the material with the tool, and plan on numerous passes.

I think back to high school shop where we turned table legs on a lathe and took off 1/1000 of an inch at a time with a razor sharp edge, and made a zillion passes. Nothing overheats, nothing grabs and digs in, if you take one too many passes you only have a 1/1000 error.

Working inside a kayak requires careful placement and elbow bracing to avoid dropping the belt sander and cracking or cutting through the hull, also goggles/ breather and a good light.

I asked about small sanders to get in tighter spots. My 3x21 is ok for the coaming but thats as small as it goes for inside radius