General Exhaust Discussion

[Clyde A. Phillips]

This will not answer the question about mufflers but will provide some ideas about the rest of the system.

Since I never installed the engines, but was aboard many of the boats from about #90 on to the end, I have taken note of some construction features. The exhaust line from the engine to the transom was made up of a few sections, similar to the drawling above, that were made of an inner tube (not the rubber type for tires; just a tube inside the total) enclosed in a tube of larger diameter.  The outer tube was fastened to the inner tube with a section of sheet metal rolled into a conical shape and brazed together as shown.  Material, thicknesses, diameters and such should be decided by someone with proper background.  I expect Bob could help with that.  My memory is that they were of copper, but I am doubting that now.  Diameter of the inner tube could match the exit on the engine.  Lengths and number of tubes would be what is necessary to get the exhaust out through the transom.  The outer water jacket tube didn’t impress me as being twice the diameter of the inner tube, but it must carry enough water to cool the exhaust.  The nipples brazed on the ends of the water jackets are to receive high temperature resistant hose to carry the water from one section to the next.  One area of the system, probably from the muffler to the transom, should have a “loop” in it, high, near the center of the boat, to prevent water from entering the boat via the exhaust system.  I think there are pictures somewhere on this site that shows at least some of the exhaust system.  I remember that at Dorchester the entire setup was made at the yard, including the muffler. 

Don’t thank me for my help because I have left you with many questions unanswered!

[Eddie Offermann]

The were indeed copper - I still had the original until recently, but age and corrosion had taken a toll on the exhaust line/water jacket combo, and that combined with the increased water flow required for the replacement engine ultimately suggested that we needed an all new assembly. The new one is stainless.

[Clyde A. Phillips]

Glad to hear you are all fixed up.  Stainless is almost always a good way to go.  Duplicating original equipment, with boats the age of these, may just keep you in the dark ages.  Every chance possible, upgrade.
 
Eddie Offermann said:

The were indeed copper - I still had the original until recently, but age and corrosion had taken a toll on the exhaust line/water jacket combo, and that combined with the increased water flow required for the replacement engine ultimately suggested that we needed an all new assembly. The new one is stainless.

[bob mitchell]

Eddie, and Clyde as well- I am working full time and just can't put my hands on the pictures I want,  After the manifold exhaust elbow comes the silencer, a fiberglass chamber, that fills with exhaust water until the exhaust gas pressure "burps" it out. I could not find my photo of the main silencer. The little exit I show in the transom is another resonance silencer.

It is worth mentioning that I think the siphon break for the exhaust is on the heat exchanger! Check that out and let me know. Exhaust stuff is really important - your exhaust may work until it doesn't, at which point your boat may sink. Highly recommend, once again, Boatowners Mecxhanical and Electrical Manuel, Nigel Calder. My impression is that you might have an originl set up, whereas mine has been modernized. I say this because I have no metal in my system aft of the manifold elbow.

[Clyde A. Phillips]

Bob, and anyone else.  As the Newporters went out our doors the system was all metal.  Yours is surely updated, maybe a couple of times.  Since the system is mostly above the water any sinking would happen if the engine is running and it pumps the cooling water (by now hot) into the bilges.  Not a happy note whether it sinks or not.

I agree on Nigel Calder as a good resource.  I have none of his books but have read enough of his articles to know I would listen very closely to what he says and I would curse the day I didn't agree with him.