It was a loud thump in the dark about 0530, but no damage was done. This sailboat on the mooring to the S of us just happened to swing 180 degrees from the direction we and the other nearby boats were facing and it hit.

Most moorings are close enough together that two adjacent boats swinging towards each other will collide, but that is not that common an occurrence. Since it has happened several times here already in 24 hours, I conclude these moorings are way too close together.

BTW, we gulped and paid $4 per foot (yikes!) to move to the Kennebunkport marina for the night. We now have power plugged in and the heater available at any time.