Converting Dry Exhaust to Wet

[DiverDan]

I currently have a dry stack on my 32' 1970 Charles Hankins and I have been pondering changing it to a wet exhaust. I know, why change the simplest and easiest to a possible problematic? Well, the dry exhaust gets really hot, and with the diving activities, or even being on the deck in sloppy seas, I do not want a passenger getting a nasty burn.

http://www.wreck-finder.com/Wreckfinderside.jpg

You can see the stack just to the left of center in the image. The gear up bench for diving is immediately behind it. I thought about building a box around it that would be lined with flashing, but I am worried about the heat not being able to dissapate propperly.

I already have a raw water pump that only services the oil and trans coolers (engine is keel cooled) so that is not an issue. The manifold is above the water line, so that should not be an issue either. Suggestions????

Thanks,

dan

[WWheeler]

how about a fake engine stack in the style of the Queen Elizabeth? Fake, but functional. Or a small railing that goes around it?

[John E Hardiman]

Originally posted by WWheeler:
how about a fake engine stack in the style of the Queen Elizabeth? Fake, but functional. Or a small railing that goes around it?Actually, most "real" stacks use the intake air to cool the stack caseing. The exhaust uptake is surrounded by the engine room air intake plenum with everything sized so that the stack gas temperture is just above condensation tempture when it exits. This serves the three fold purpose of insulating the uptake, heating the inlet air, and increasing boiler efficiency. It would very very slighty decrease diesel or gas efficiency though due to the slightly higher inlet air temperture though with a large enough air gap this would be insignifficant.

A light metal stack casing would the fastest and most likely cheapest option. Going to a wet exhaust generally requires a change of exhaust manifolds, special high-heat hoses, wet muffler, through hull fittings,etc...

[Adam C]

All of our dry stack Nordhavns have a perforated exhaust shroud expressly for this purpose. It essentially looks like what you'd see on a semi-trailer's stack....a full length cylindrical shroud with many round holes.

Works great, and cheap.

[Gary E]

Dan,
I had much the same thing with a Luhrs. I am going to assume the manifold is cooled by the Keel Cooler and the raw water is discharged overboard after going thru the oil coolers.

There are several things that I would sugest you look at.

The output connection of the manifold to the muffler you now have....it is probably a large NPT pipe thread.. this needs to be either the cast iron straight type or riser type if you need additional height to protect the engine from a wave that hit's the transom sending a dose of water up the pipe into the engine, that will dammage the engine.

You did not say what engine you have, but Barr Marine in the Phila area or http://www.marineengineparts.com/ should be able to help with that casting. I would want the output of that riser to be as high as reasonable so water is kept out of the engine. The output of the raw water pump is now used to cool this riser and then sent overboard thru the exhaust pipe.

Once you have that set, then I used a large copper pipe to a muffler, then more copper pipe to the transom. I want the hole in the transom to provide the most drop from that pipe to the water I can get, it makes it harder for water to run up that pipe and kill the engine. BTW...keeping the engine on while drifting or at anchor is sloppy weather will help keep that pipe's water flow going the right way.

This worked well in the my Luhrs that had a Gray 6 cylinder, it should work well for you.

Gary

[nedL]

Dan, She is looking good. I'll just add the comment that one way to keep the cost down would be to run the wet exhaust out the side near the engine rather than running back to the transom. This will also keep the exhaust away from where you are diving.

[DiverDan]

Thanks Ned, still a lot to do on her, but we wanted to run her this summer. The diving has been great, and the boat doing well. We had one tranny problem, but that was easily solved.

I thought about running the exhaust to the side, but worried that there would be a lot of fumes in the cockpit, but I guess no worse than there is now with the dry exhaust.

For the one who asked, the engine is a '83 Lehman 120.

What I was thinking of doing was comming off the npt fitting with a 180 degree elbow (the fitting now goes up for the current exhaust). Then placing a short 6-12 inch nipple, then a Tee or Y into which the raw water will flow. There is room to make the 180 degree elbow about 6 inches above the top of the engine, and the top of the engine is a good 18 inches above the water line.