5432 exhaust elbow
- Thread starter John Hines
- Start date
Steuermann
Member II
Caution: I did that many years ago on our '67 Cal 34 which also had an Atomic-4. But only a few years later while motoring 35 miles uphill to Catalina island I lay down in the v-berth to take a nap. Dead flat calm, hatches and ports all open tiller-pilot on and friends in cockpit on watch. After about 15 minutes I knew something was wrong. Stumbled topside and friends said I looked terrible. Face very red and felt dizzy and nauseous with a raging headache.
Didn't know what caused it until we pulled the engine while we replaced the At-4 with a Universal 25 diesel (see: The Do-It-Yourself Diesel, SAIL Magazine, March, 1987). The dry portion of the exhaust, which I had fabbed out of 2" galvanized water pipe, was holed like Swiss cheese so badly I could fold it in half by just stepping on it. It had corroded through and exhaust leaked through the layer of asbestos (yes, asbestos) tape insulation. This was in the days before CO detectors were available.
Based on what happened, I wouldn't recommend using galvanized pipe on a dry exhaust. At the very least, PLEASE make sure you install and regularly test a carbon monoxide detector. I understand the ABYC now requires them on new vessels and if you ever have a survey, the surveyor will list that in Category A (mandatory).
Didn't know what caused it until we pulled the engine while we replaced the At-4 with a Universal 25 diesel (see: The Do-It-Yourself Diesel, SAIL Magazine, March, 1987). The dry portion of the exhaust, which I had fabbed out of 2" galvanized water pipe, was holed like Swiss cheese so badly I could fold it in half by just stepping on it. It had corroded through and exhaust leaked through the layer of asbestos (yes, asbestos) tape insulation. This was in the days before CO detectors were available.
Based on what happened, I wouldn't recommend using galvanized pipe on a dry exhaust. At the very least, PLEASE make sure you install and regularly test a carbon monoxide detector. I understand the ABYC now requires them on new vessels and if you ever have a survey, the surveyor will list that in Category A (mandatory).
Your account of the swiss cheese pipe is scary and not to be taken lightly. I think the issue lies more with the header wrap than the actual pipe material. I've seen all flavors of exhaust magically disintegrate when wrapped,but usually after a much much longer service life. I've seen pipes of stainless, iron and general tubing all fail when wrapped sooner than the pieces they were attached to. At least to the point of the water injection, you're going to have to run some sort of pipe. On older installations I've seen, it has almost always been galvanized. Galvanized is now frowned upon due to the risk of fumes when new, and black iron pipe is often used in it's place, but I don't believe it lasts as long. I opted for galvanized and made a point of some initial motoring for the purpose of heating it all up and cooking off whatever wanted to. I've never had any issues on several boats now, but obviously different conditions can yield to different failure rates. I'm sure the brackish water of the Chesapeake is far more forgiving that the higher salt of the ocean when it comes to this type of failure. Regular inspections of the system are in order.
The best thing is to limit the length of pipe in the system. I have the vertical space in Emerald for a 90 off the manifold to perhaps an 6" piece of nipple with the mixing elbow on top and then exhaust hose from that point all the way aft, going via the Centek waterlift in the process. Unfortunately, on the E-27, there isn't enough vertical space to do this with an Atomic 4, hence the shot out the aft part of the engine compartment and jog to the port locker. Now, I have a friend with an E-27 and a Yanmar YSB-8, and that cute little engine is short enough that it fits under the deck, and you can do enough rise to the mixing elbow to make it all fit. It's close though. The underside of the engine compartment lid has been relieved in the area to squeeze it all in.
As always, the above is worth what you paid for it
The best thing is to limit the length of pipe in the system. I have the vertical space in Emerald for a 90 off the manifold to perhaps an 6" piece of nipple with the mixing elbow on top and then exhaust hose from that point all the way aft, going via the Centek waterlift in the process. Unfortunately, on the E-27, there isn't enough vertical space to do this with an Atomic 4, hence the shot out the aft part of the engine compartment and jog to the port locker. Now, I have a friend with an E-27 and a Yanmar YSB-8, and that cute little engine is short enough that it fits under the deck, and you can do enough rise to the mixing elbow to make it all fit. It's close though. The underside of the engine compartment lid has been relieved in the area to squeeze it all in.
As always, the above is worth what you paid for it
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Afrakes
Sustaining Member
Various sources of corrosion
The joys of fresh water. No salt to worry about. When I cut my old stand pipe open only the upper third of the inner exhaust carrying tube was deteriorated. The outer black iron tube had not suffered any significant material loss. I don't know how long it had been on the boat. The absence of extra fasteners scars on the bulk head led me to believe that it was original. Though I doubt it, on a 40 year old craft. Al Frakes, Port Kent, NY
The joys of fresh water. No salt to worry about. When I cut my old stand pipe open only the upper third of the inner exhaust carrying tube was deteriorated. The outer black iron tube had not suffered any significant material loss. I don't know how long it had been on the boat. The absence of extra fasteners scars on the bulk head led me to believe that it was original. Though I doubt it, on a 40 year old craft. Al Frakes, Port Kent, NY
Steuermann
Member II
Not to whip a dead seahorse any longer than provides one enjoyment, but leaving a dry header pipe unwrapped belowdecks is an excellent way to start a fire, should something fall against it in a seaway. Like a fender from an adjacent cockpit locker. Don't ask me how I learned about that. 8^0
I haven't looked up the ABYC/USCG regs for dry exhaust; perhaps someone else can chime in. I think dry exhaust must be wrapped belowdecks. Every powerboat, every professionally installed marine auxiliary I have ever seen has had the dry portion wrapped.
The exhaust system I mentioned was an old standpipe muffler exhaust. I cobbled together an exhaust riser out of 1.5" or 1.75" weld-ells and welded them together. Took one of the cockpit drains off and used it to determine the waterline height and then taped up a few 1.5" weld-ells until they were positioned correctly, took them home and welded them up with a stainless wet elbow at the end, so only had about 8" of rise to get to the point where the elbow was well above water level when heeled severely to starboard. The wet elbow connected to 2" steam hose which connected to a stainless waterlift muffler. The output from which, rose to cockpit seat level, then ran aft to the transom exhaust outlet. Never had any problem after that.
Wrapped the dry portion of the new exhaust header with 2" fiberglass tape, held in place at the end with a hose clamp. It smoked a bit (sizing?) when it first got hot, but had no problem for 2200 hours of engine time after that until we sold the boat.
As you say, limiting the length of the dry portion is likely the key.
I haven't looked up the ABYC/USCG regs for dry exhaust; perhaps someone else can chime in. I think dry exhaust must be wrapped belowdecks. Every powerboat, every professionally installed marine auxiliary I have ever seen has had the dry portion wrapped.
The exhaust system I mentioned was an old standpipe muffler exhaust. I cobbled together an exhaust riser out of 1.5" or 1.75" weld-ells and welded them together. Took one of the cockpit drains off and used it to determine the waterline height and then taped up a few 1.5" weld-ells until they were positioned correctly, took them home and welded them up with a stainless wet elbow at the end, so only had about 8" of rise to get to the point where the elbow was well above water level when heeled severely to starboard. The wet elbow connected to 2" steam hose which connected to a stainless waterlift muffler. The output from which, rose to cockpit seat level, then ran aft to the transom exhaust outlet. Never had any problem after that.
Wrapped the dry portion of the new exhaust header with 2" fiberglass tape, held in place at the end with a hose clamp. It smoked a bit (sizing?) when it first got hot, but had no problem for 2200 hours of engine time after that until we sold the boat.
As you say, limiting the length of the dry portion is likely the key.
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Steuermann
Member II
Welllll, not really. It's not the salt so much as the environment within the exhaust system. The corrosion in the dry portion of the exhaust header proceeded from inside out. Here's how:
There were no deck leaks, no salt spray that ever got down to where the engine is. The dry exhaust terminated in a stainless steel standpipe muffler to which the raw cooling water outlet was attached. When the engine was turned off one end of the dry exhaust terminated in the closed airspace over a couple of quarts of seawater. The other end of the dry exhaust terminated at the exhaust header. So the environment within the dry section of exhaust was exposed to saturated humidity all the time the engine wasn't running.
As the sun beat down on the cockpit floor during the day while the boat sat in her slip, the temperature in the engine compartment rose. So did the vapor pressure of the water in the standpipe muffler, increasing the concentration of water vapor within the dry header line. Then when the sun went down and temperature dropped, moisture condensed on the inside of the dry section and residual sulfur from the combustion products of gasoline made weak sulfuric acid which started to eat away at the inner surface of the header. Eventually pinholes developed and got bigger and bigger . . .