OK so I have always been an outboard guy but the new PQ has a 7.4 inboard with thru hull exhaust.

What keeps water from backing up the pipes and going into the engine on say a quick deceleration or if it is tied up and a swell comes at the back of the boat.

I know this is stupid but just trying to be safe and not have an issue down the line.

Thanks for not laughing too loud!

Internal or external flappers. If you don't have them, get them now!

Would the boat have had them from the factory?

It DOES NOT have external flappers that I know

The boat is 10 years old and has not had an issue I am just trying to prevent one.

Thanks a bunch for the reply

Look inside the exhaust tip, there should be a metal/rubber one way valve (flap) in there... If not, get some replacements or go external!

The internal or external flappers prevent water intrusion when the boat is not running. Also, if it has mufflers, they will help prevent water from water from coming in. When the engine is running, the exhaust pressure is what primarily prevents water from coming back up the pipes.

external flappers are better for keeping water out. mainly because you can see them. internals can fail-burn away or stick. and you have no way of knowing...i am thinking of 4 big plugs for overnight (or all week) tied to the dock.

When decelerating, do not pull all power. Keep light throttle and keep slow forward speed to prevent the backwash from crashing into the stern. This will prevent the water from entering with great force into the exhaust port. Also, like was said, flappers are needed if not internal.

My 232 had internal flappers since I had captains call. If I had the exhaust open and the boat died they automaticly closed, the internals only open with exhaust pressure when the engine stalls the spring shut. But when I first bought the boat I had the drive off and out came to metal flappers. At some point the the rubber coating burnt off and they fell down to the drive. Hard to check internals but def have the externals.

I have the internal flappers that look like this (look up the exhaust pipe):


and the external flappers that look like this:


I would do both.

The externals are a lot less hassle. I found some of the internals to be too noisy.