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PT Boats - General
Post a reply to: Elco exhaust
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[StartQuote] Hi shipmates I am pretty sure we discussed this subject before on this discussion board, maybe about a year ago. I think Dr Al Ross answered the question definitively. I am comparing it to the exhaust pipes on our 78 ft Higgins PT658. On the 3 Packard engines we have, the engine exhaust manifolds are cooled by the sea water. The sea water then enters the exhaust stack cooling water jackets. The sea water does not actually mix into the exhaust inside the stack. The exhaust stacks, and I believe the Elco boats used a similar arrangement, are literally a "pipe-within-a-pipe". The exhaust gases stay within the inner pipe, and there is a spirally wound flowpath for seawater between the inner pipe and the outer rubber hose. The spiral wound flowpath prevents any hotspots from forming. The outer rubber hose and inner exhaust pipe connect to the "through hull" fitting which connected to the muffler, where the water is mixed into the fitting to keep it from getting too hot and catching the wooden hull in contact with the fitting on fire. We actually caught some of our engine room on fire before we recreated what they originally had in 1945. The fact that the water is not mixed into the exhaust in the inner pipe is important because when the engine is secured, there is the possibility that the water in the pipe will contract and suck seawater back into the engine exhaust valves and cause a lot of problems. It is also very important when starting the engines to ensure seawater is actually flowing inside the stacks soon after starting the engines. It is possible to get a vacuum lock of sorts and if it forms and prevents water flow through the stack you could easily cause them to melt from the intense heat. These engines literally blow flames out of their exhaust at high rpms when burning 100 octane gas, and the temps can easily exceed 850 degrees F. Not good on a wooden PT Boat. I hope this is helpful info. Jerry PT658 Portland OR Jerry Gilmartin[EndQuote]
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