Roll n Rock

This entry concerns last night's anchorage in Joshua Cove, which you may recall was exposed to some 1 ft. or so rollers from the SW. At first it wasn't so bad since the wind kept Spray sort of aligned with the waves, but then the wind disappeared, and Spray aligned herself beam-to the waves, which were of a period close to Spray's natural roll period.

So as I was trying to fall asleep, it went like this:

roll roll roll roll roll roll roll roll ROLL ROLL roll roll roll roll roll roll roll roll

and repeat. The big ROLLs were sliding things around in cabinets and making a racket, so it was impossible to sleep.

In the absence of wind, why did Spray align herself beam-to the waves? Here's my theory: If Spray is aligned bow-to or stern-to the waves, she rocks (fore and aft) rather than rolls, and her propeller moves up and down through the water. I think that produces a twist on her to turn her beam-to the waves. When she rolls (side to side) with the waves, there is no such propeller motion and no twist. So the stable postion for her is beam-to the waves.

So I got up and put my stern anchor in the dinghy, rowed it down-wave a hundred feet or so and dropped it in. Back on spray I tightened up on that stern line so Spray was forced to point directly into the oncoming waves. Now she rocked a bit but did not roll, and the rocking was quite tolerable.

The moral of the story? A little light rock makes for a better night than a hard roll.