Replying to the JohnLee post--the other lost cowl I know about belonged to Captain Charlie. I think he said his disappeared pretty fast, but the water was probably murkier (lake).
Truenorth, yes everything I've read says they are pretty flimsy and unreliable. I'm not all that enamored of the way the cowl vents look--more of an affectation to me. Hope I didn't offend anyone with that comment--it's a matter of personal preference, not judgement.
I am planning to add a solar panel at some point and I will probably install flat vents with electric fans I can turn on and off. They would be powered by the boat's solar/battery system. None of the fans are electrically reversible because of the blade design, but I have found one or two that can reverse direction by removing and reversing the blade. At least that's what they claim--doesn't make sense to me because if you reverse the blade it still tilts the same way. Maybe they meant to say you can change one blade out for another that has reverse tilt. I'm thinking of one vent pulling air in and one pushing it out, but that might not be a good idea because they are so close together.
Not worried about the vents leaking into Dorade boxes.
Anyway, thanks for the input.
Follow my progress (very little so far) at
http://danacolepocketshipbuild.blogspot.com