Water-cooled dry exhaust ?
I have a strange hybrid dry / wet exhaust and wonder if anyone else has a similar set-up.
The boat is a 54' sloop rigged motorsailor with a 135 HP Ford Lehman diesel. The cooling is primarily a fresh water keel cooled system, but there is a sea water pump that provides cooling water to an oil cooler and transmission cooler, and to the exhaust.
The exhaust comes out of the back of the water jacketed manifold, and through about 12" of conventional dry exhaust pipe. At this point there is a 'collar' around the exhaust pipe into which the cooling water goes. Out of the collar come about 24 1/4" diameter copper pipes which are bundled around about another 12 feet of dry exhaust, all wrapped up together inside insulation. This exhaust line runs aft from the engine space into the space under the cockpit, then up to under the deckhead. At the top, the bundle of small lines go back into another collar, from which a single line carries the water into the muffler. From the muffler, conventional wet exhaust hose carries the wet exhaust out through the stern cabin into the transom.
Here's a sketch of the set-up...
The collar where the cooling water goes into the bundled pipes has rusted out, and the connector has broken away. I'd like to just go to a straight wet exhaust the whole way, but wonder why it was built this way to start with. The whole length of run is about 20' of 5" pipe.
Anyone got any input?
The biggest 'high riser' Ive seen.
Is engine far below waterline?
Might even be a way of reducing back pressure if distance from engine to exhaust outlet is long.
My A4 gas motor was done a bit like this as it was a common way at the time
This design exhaust system was very common until the 1980s when 'water lift' mufflers became popular. The 'jackets' were usually made of heavy copper and the 'stack' was vertical with the 'injection' water entering countercurrent (from the top) into the 'stack' .... the price of copper eventually made such design very expensive.
The only real problem in such 'wet stacks' is when a pin hole developed between the wet side and the dry side the leakage wasnt 'visible' and eventually would 'back flow' into the engine ... the shut down and 'cooling' engine developing vacuum and drawing the leaking 'stack water' into a combustion chamber - ouch.
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