For the 31 AO does everyone have flaps in the exhaust tips?

no. I do not run flaps in my personal boats and have removed any metal flaps from any boat we built. They only rattle and make noise. I now run GGB mufflers and have removed the rubber flaps in them also.

Do you ever have problems with reversion?

no problem with reversion

If interested in quieting it down, take a look at homemade Snufflers.

I am interested in solving a potential issue with water coming into the motor from the exhaust when the motor is not running or is at a idle. As low as the exhaust is when the engine is shut off it would not take much of a wave to push water in the exhaust.

CMI makes a transom tip with baffles. Give Ateco a call.
847-623-2737

Haven't had any problems yet. It appears there's enough of an angle that water can't make it uphill far enough to get in headers. Backing down scared me at first, but so far no issues. At idle they sit about an 1/2 above the water. The one thing I don't like is they spit at you at idle and backing up. Get's water on the back deck.

I would also think it would depend on headers/manifolds. I have stainless marine manifold style exhaust, headers would have more fall I would think. I have one motor with milky oil and a slightly bent intake valve, everything has been checked for leaks and there are no leaks. I can only assume the milky oil and the bent valve came from the same issue, a hydrolock. I am putting flaps in the exhaust just to be safe.

Yep. That's what it sounds like. Had tofigure out how to cut down a MOV file. Attached a MPG file.