Exhaust outlet goes under when motoring!

[peters.carl]

I have an exhaust outlet in the stern of my 26ft cruising keelboat boat. With the boat in its marina berth it sits about 80-100mm above sea level. With the boat underway it sits below the level of water at the stern because of the stern wave. The engine runs fine and pushes water out under pressure, and we have a riser to prevent ingress, but is this putting extra back pressure on the exhaust and should I raise the exhaust outlet? Is this a common problem? How high does the outlet need to be? I guess above the level of maximum waterline with the boat underway?
Many thanks

 

[yoda]

Quite normal so leave well alone. if it's running fine then there is no need to change it.

Yoda

 

[peters.carl]

I should add that it sits underwater by about 50mm constantly when underway. Doesnt just bounce under with the occasional wave. This still okay?

 

[AngusMcDoon]

Outboard engines' exhausts are under water all the time. Doesn't seem to harm them.

 

[higler]

There is a Moody 35 next to me and his exhaust is underwater even at anchor, I did mention it and he assured me its how its supposed to be and it cuts down noise and any fumes.

 

[CharlesSwallow]

Some might say that if there is enough wind to heel the boat that far then there is enough to sail, some might say!

Chas

 

[MoodySabre]

Moody 31s are designed that way. Does mean that there is a bit of steam sometimes but nothing to worry about.

 

[G12]

Mine does the same as do loads of others, nothing to worry about.

 

[Red Admiral]

Outboard engines' exhausts are under water all the time. Doesn't seem to harm them.

The very fast wartime MTBs took their exhausts through the bottom of the hull towards the stern presumably to help silence them in covert operations but also, apparently, to reduce fuel consumption whilst planing.

 

[jakeroyd]

i would agree with others this is unlikely to be a problem. My moody 27 whent vertically down like most moody's.
You shoul find a high loop in the hose which protects against water flowing back into the engine

 

[rob2]

In a chop mine goes in and out of the water making some very strange noises - a sort of slow ululation (sp?). If you mount the outlet higher than necessary, you may no longer have sufficient height in the swan neck so it will risk backflow into the engine, best avoided.

Rob.