I picked up two of these at the Annapolis boat show a few years ago. I tried to find the company on the web to buy more but couldn't. Our family calls them "dinghy butt pads" and we carry them in a backpack while ashore. They fold up smaller than foul weather pants, are easy on/off, and keep our butts dry from dew and moderate spray on the dinghy tubes.

Length (waist to bottom) is about 30", width (point to point) is about 58", width along attached part of waist is about 30". The points on the sides form "wing flaps" that can be wrapped around your thighs to protect them from spray.

This size works well for most people. You could scale it up for wide bodies, or smaller for kids.

The tag says "waveslicker". This one in the photo was made of a treated waterproof denim that has required annual re-treating, but the ones we made for our kids were Naugahyde and work better. We're going to make a few more to replace the denim ones.

No more wet butts!