|Update: Flopper Stopper||
Stopper: A drag device, to lessen the effect of swell which causes the
boat to roll, or flop from side to side. The flopper stopper is suspended
from a spinnaker pole which holds it away from the boat, with a line from
the masthead attached.
In Gibraltar, Graham constructed two of these flopper stoppers, using a triangle of 3/4" marine ply and three dive weights to make it sink.
The idea is that when the boat rolls, the flopper stopper is encouraged to descend by the heavier weight attached to the leading point. As the boat rolls the other way, the flopper-stopper rises into a horizointal position in the water, thereby creating a larger surface area for water pressure to act upon it as a brake to the motion. This dampens the roll and effectively lessens the need for a stern anchor (or hotel booking).
In moderately rolly conditions, one flopper stopper is sufficient to dampen the motion, but in more severe swells, one can be set on each side.