Exhaust Outlet at Waterline

I have a new Rescue Minor diesel powered inboard runabout. This unit uses the typical water cooled exhaust system. In the particular implementation of this water cooled exhaust the line runs from the exhaust manifold, down at a sharp angle to a muffler and then at a declining angle to the transom exhaust fitting very much as demonstrated in this image:


My question is about the height of the exhaust outlet at the transom above water line. Presently, the bottom of the 2" exhaust outlet is just 3/4" below static water line. The placement of the outlet was such to allow for a natural drop in the exhaust hose to allow water to drain out exhaust outlet when at rest.
Is the placement of the exhaust outlet so close to the water line at rest a problem?

 

Sure there may be problems. What system is to prevent seawater from entering the exhaust pipe?

 

That is pretty typical. The section of pipe forward of the Y is a surge protector. You could install flaps to help prevent backflow when going in reverse.

 

Not only when going in reverse.

 

I don't see anything wrong with the above diagram. Exhaust exits can be anywhere, though at or near the LWL tends to keep the pipe cool and can soften noise if positioned right.

 

Nobody says that the diagram has something wrong. I simply miss some element that prevents seawater back flow.

 

The usual solution is a nice 90deg bend aiming the exhaust at the water.

Slowing down the 90 will go submerged , but will not pump water up to the exhaust manifold.

 

Or better yet, the siphon tube and a butterfly valve.

 

There is a surge pipe in the diagram

 

What if there were no surge pipe in the installation?

 

Then the safety margin will be less.

 

I have owned several inboards with exhaust submerged up to a ft under water when stationary and they only had rubber outlet flaps. I have never had a problem.

 

This one has the outlets right near the bottom and the manifolds have no risers or surhe pipes.

 

The Rescue Minor is a pretty shallow hull, so the slope down to the transom needs to be as exaggerated as practical. Flaps work well as does a surge chamber. Is this a straight shaft setup?