And that includes sailboats under power. You can't hear as much, in the cockpit but especially down below, you hear nothing outside.

Reminds me of the lobster yacht off Stonington in a thick fog. There was a light wind blowing that had us sailing about 3kts. I could hear the powerboat slowly turn toward us(I've had this happen before and know what they're doing- 'radar hunting'). With the clear engine sound, I could tell about where it was when it broke through the fog so I eased the sheets and slowed a bit as they approached.

A woman finally came out of the cabin and stepped up into the cockpit, and began looking. When she finally spied us, she yelled, "You're are completely invisible to radar!".

She stomped her way back down below and they goosed the throttle and left us in a cloud of smoke.