I'm running center rise aluminum exhaust manifolds on my BBC.  Do I really need to run the flappers at the exhaust tip.? Can the water run up the hose? The tips are at or just below the water line. I'm all it the worried about a boat going by and putting out a wake big enough to run up the hose while I'm floating or beached. What are your opinions?

Thank you. you convinced me.

I have the Idmar center rise exhaust and lock my motor up twice the first year I had it.
Bought the big ugly flappers that mount over the the trumpets.