This is an ingenous cover my wife made for the helm. There is a "pocket" the same shape as the wheel that slips over the bottom half of the wheel. The rest of the cover just pulls up and snaps on to the top with 6 snaps screwed into the fiberglass along the narrow ridge just below the window. There is some elastic along the sides to keep things taught.

This one is kind of ugly, but functional. In addition to covering the lower end of the drive leg, it keeps the aft dock lines from getting fouled in the prop. There is some foam between the layers of Sunbrella around the bottom to form a kind of stiff "box", and to keep chafing down.