How high above the water should my exhaust be?

[demonboy]

We're a 43ft boat with an inverted transom. We are looking at designing a swim platform but it would have to be quite high in order to clear the exhaust. It is approx 370mm above the water line and I'm wondering if it's ok to move it down by 50mm, 100mm if possible. Of course there is a u-bend in the exhaust but would 270mm be too low?

Appreciate your thoughts, cheers.

 

[Ruffles]

Mine is below water level!

I've heard there can be problems with a following sea defeating the U bend and I believe some 'blue water' boats fit a sea cock for this reason. But in general I can't see a problem at all.

 

[Dave_Seager]

It does not matter much where the exhaust goes through the hull provided that the bend on the inside is high enough to protect the engine. Most motor cruisers have their exhausts very close to the waterline. Outdrives and outboards have exhausts well underwater although they do have a small outlet near the waterline to reduce back pressure when starting.

 

[Danbury]

You can get transom outlets with integral check valves if you're worried about water ingress...

 

[NormanS]

Mine is on the port side, so is well under water if I happen to be motor-sailing on starboard tack. Doesn't bother it.

 

[dylanwinter]

slug and beast

Mine is on the port side, so is well under water if I happen to be motor-sailing on starboard tack. Doesn't bother it.

the beast had an elastomuffle

no longer made

so it no longer worked

the exhasut was about six inches above the water

this was fine until when the boat changed hands they put her on a mooring where she went over on her side when the tide ebbed

as it returned the incoming tide would catch the edge of the transom and it would occasionally make its way back up the exhaust system

it never happened when I had her but it did give Richard some problems

D

 

[claymore]

Isn't the key to have it sufficiently above the waterline so that should a bit of the exhaust plumbing fail, the boat won't fill up?

 

[pvb]

...I'm wondering if it's ok to move it down by 50mm, 100mm if possible. Of course there is a u-bend in the exhaust but would 270mm be too low?

As long as there's a good U-bend, the exhaust outlet can even be under water. I think it's better for the outlet not to be permanently under water, as it's easier to visually check the presence of cooling water. The outlet on my Hallberg-Rassy is at the waterline.

 

[sailorman]

all info on the Vetus website

 

[coopec]

Mine is on the port side, so is well under water if I happen to be motor-sailing on starboard tack. Doesn't bother it.

I will be installing the exhaust through the Port side as well. I'm sure I read the exhaust should exhaust 5+ in above WL. That's not going to help much if sailing on a Starboard tack (as you say) or in a seaway. Comforting to know that is not a problem.

 

[ghostlymoron]

This diagramme may be useful.

 

[claymore]

As long as there's a good U-bend, the exhaust outlet can even be under water. I think it's better for the outlet not to be permanently under water, as it's easier to visually check the presence of cooling water. The outlet on my Hallberg-Rassy is at the waterline.

So, when the pipe comes off/ fails at the skin fitting, all will be fine, will it?
I don't think so.

 

[sailorman]

high loop n waterlock of a capacity to hold /contain the water in the exhaust

 

[claymore]

high loop n waterlock of a capacity to hold /contain the water in the exhaust

If the pipe comes off at the skin fitting, the boat will fill up with water if the skin fitting is below the waterline.

 

[sailorman]

If the pipe comes off at the skin fitting, the boat will fill up with water if the skin fitting is below the waterline.

really

 

[claymore]

Yes really, so all the posts suggesting its ok to have an exhaust outlet below the waterline are ill-advised. Or do you disagree?

 

[sailorman]

Yes really, so all the posts suggesting its ok to have an exhaust outlet below the waterline are ill-advised. Or do you disagree?

fully agree
how does an engine cope with the back pressure

 

[claymore]

Thats a shame, I'm just watching Scotland getting stuffed by Wales, an argument with you may be just the diversion I could do with!

 

[NormanS]

If the pipe comes off at the skin fitting, the boat will fill up with water if the skin fitting is below the waterline.

Most boats have several skin fittings below the waterline, which have pipes or hoses. Wow! What should we do?

 

[claymore]

Most boats have several skin fittings below the waterline, which have pipes or hoses. Wow! What should we do?

Close the stopcocks when not on the boat is a start
Keep them serviced
Check regularly
Cross fingers