Exhaust outlet under water

[jcr]

I have recently loaded up my yacht for a long trip and added self steering gear and a radar antenna to the stern. At hull speed, all vessels squat at the stern. I now find that my exhaust outlet (near the bottom of the transom) is fully underwater at hull speed. The exhaust system includes a water trap, anti-syphon and 18 inch gooseneck, which is fitted vertically. There is room under the sterndeck to raise the gooseneck by no more than 2 inches, which is not enough. There is not enough room to angle the gooseneck by any significant amount in order to further raise the outlet.

The problem is further compounded by the fact that my transom is at a negative angle of 45 degrees so that exhaust fumes and cooling water are well and truly trapped.

This must result in back pressure which will adversely affect the engine efficiency, if not engine life and reliability.

Any advice will be gratefully received.

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[pete]

Hi
Sorry no solution but I fitted an Vetus exhaust waterlock last week and the Paperwork with it said that the bottom of the exhaust outlet must be at least 5 cm above the water line.

Pete

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[Anchorite]

Hi Pete: 5 cms above the wl when the boat is at rest. If the transom dips at
hull speed there is a fair chance that rather than back pressure you may get
a venturi effect on the exhaust (i.e. positive pull). Is there any noticable loss of
performance when the transom squats?

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[hlb]

I cant see it will make any difference. My exhausts are partly submerged at rest. They must be a good two feet under at times. Your boat cant have dropped that much, less you have added umpteen tons. Ever thought how much there underwater in a big following sea?

<hr width=100% size=1> <font color=blue>No one can force me to come here.<font color=red> I'm a volunteer!!.<font color=blue>

Haydn

 

[jcr]

thanks for the replies. I have been doing a bit of research and it seems that some systems are deliberately designed to exhaust under water. There is no noticeable difference in performance, but how this came to my attention is that after a few hours motoring my transom and the boot line were quite badly blackened from the exhaust gases condensing under water. I intend to fit a Vetus water/gas separator so that I can vent the water out of the present outlet and the exhaust gases out of another, much higher above the water line.

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[colvic]

We were the same for over four years and it made no difference over some 5000 miles travelled.

Phil

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