Which exhaust flaps are good for a through hull where I cannot get to the outside? My boat has the silent thunder exhaust that blows through the boarding platform and the flaps are burned away. There are loosely mounted vertical shafts in the 3 1/2" ID thru hull tubes that are on some riveted mounts. I'll do some looking, but if anyone has ideas I'm open to suggestion.

Skip this, I found some that will do.

Do you have captains call exhaust?

Mercruiser actually recommends using both - internally and external flappers

I have changed them grind rivets off instLl mew. They where available a few years ago