Diesel Exhaust

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Vek
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Diesel Exhaust

#1

Post by Vek »

Just got a new-to-me 28' almar walkaround cabin powered by a KAD43 volvo diesel with outdrive.

I've put 420 nautical miles on it so far, and it's working great.

I've been reading up on volvo diesels a bit. Generally, the exhaust systems suck for a couple of reasons: the static water level in the pipe between the turbo outlet and the drive is too close to the turbo, and the passage of exhaust thru the outdrive is terribly restrictive.

The water level problem varies from hull to hull, having much to do with deadrise and whether it's a single or dual installation. Since this is a single installation in a 24° deadrise hull, it's about as bad as you can get. Engine history names a couple of turbo failures, and I can't think of one reason for a turbo to fail besides the exhaust side getting rotten from saltwater splashing.

The restriction problem is less easy to quantify, but anecdotal evidence would suggest that rerouting exhaust around the outdrive has a couple of benefits: lower EGT and engine operating temperature, and increased outdrive life by not blowing hot corrosive crap through it.

So, I plan to do some things. There is ample good reading on marine diesel exhaust systems on Seaboard Marine's page. The general gist is: build a dry riser out of 316L stainless sch.10s pipe parts, adapt that to some sort of wet elbow, and route the mess as desired thru the transom. You can go through a lift muffler, or not.

If you reuse the factory wet elbow, make sure that when it fails and leaks, the leakage can't flow back into the turbo.

I plan to route the exhaust dry from the stbd side turbine outlet, elbowed up and back to port (over top of the rear of the engine), then point the wet elbow downward on the engine's rear portside to some sort of thru-hull low on the transom next to the drive. This will be quiet at idle, and the engine (diesel in a tin boat) is noisy enough underway that I shouldn't notice any excessive noise.

But, I need to get the wet exhaust through the hull. The real question of this windy post is: can I use 5086 aluminum pipe and/or pipe fittings for the thru-hull? Will these stand up to the wet exhaust flow? Does anyone have wet exhaust experience with an inboard diesel in a tin boat, that doesn't involve pushing it through the drive?

Thanks,
Jerry
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welder
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Re: Diesel Exhaust

#2

Post by welder »

Jerry I don't see why the Exhaust can't go through Alloy . You might also look at building a Stainless Steel through hull fitting that looks like a through hull transducer fitting , just a thought .

I would rather have Alloy if it works.
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Re: Diesel Exhaust

#3

Post by welderbob »

Over time you will get some pitting inside the pipe from the exhaust gases and salt water. There are a number of ways to pipe the exhaust thru the transom. We have done a stainless steel flange and a short piece of pipe with NON ALLOY piping on the inside connected with rubber hose. (double clamped). I have also welded aluminum pipe thru the transom and used a doubler plate. Again I like some sort of rubber exhaust hose on the inside to cut down on the engine vibration going into the transom.If you decide to use aluminum pipe, design it knowing that you may have to replace it down the road. Not sure if going thru the trouble and expense of using 5086 will make it last any longer.

Happy welding.
Welderbob
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