I'm surprised that Ann didn't mention what we do on Insatiable II: I made small holes in the center top lip of each cowl, then took 1/8 inch dacron line and ran it from the handrail outboard
of the dorade to the hole in one cowl, then to the hole in the second cowl, and then to the handrail on the other side. Tensioned the line up enough to eliminated sag but not distort the cowls. This line prevents the Boa from wrapping around the cowl fairly well, and has kept us from the dreaded clunk-splash so far (again touching wood surreptitiously).
On this boat it isn't the genoa sheets
that are the Boas, but the preventer/vang tackles on each side of the boom, but the principle is the same... might work on the OP's boat too.