Exhaust Shut-off Valves

[cal40john]

Originally Posted by Christian Van H

I cant find a diagram on the 'net, and my manual is down on the boat, but basically there is a SS muffler mounted ABOVE the manifold. Raw water is injected into this muffler and both gases and water exit the bottom and flow "downhill" and out the stern. It's extremely reliable with very low backpressure. Sorry I cant do better right now...

Sounds like a stand pipe exhaust system.

Boat Mechanical Systems Handbook - Google Book Search


John

[Christian Van H]

John, two things: 1. THATS IT! Apparently my exhaust system is also called a "Standpipe" system. 2. You just made me spend $30 on that damn book! Wow, Gerr's book looks like just the ticket for this stage of my refit. Thanks John, I really owe ya a beer (or six)!

[Roy M]

I've used a big, black Marelon ball-valve, at the bottom of the u-loop, just before the 90 degree elbow over the side. Absolutely no problems for over twenty years. The ignition key hangs on it when the valve is closed. I use a waterproof battery switch (the one with the red key) as my ignition switch to avoid corrosion to this exposed unit. For security, the power to the starter motor is shut off by an interior switch. When the boat is left unattended, the engine power is cut off and bad guys would have to enter the cabin to search for the switch. This is awkward because the 130 dB alarm sirens, inside and out, make their noses bleed and ruin linear thought processes (not present in some boat thieves).

[bobfnbw]

Redoing the exhaust system now, before the perkins comes back home after rebuild.
I think its a 2" hose, and thinking about going up to 3", so will need to replace the water lift as well as the transom exhaust. A flapper valve added seems like a good idea.
Since its a center cockpit 40 footer, its a long run to the transom.
Bob

[fishwife]

My last boat had a exhaust flap that worked for ten years without once flooding the engine. I've never heard of a flap failing but I'm sure it must have happened somewhere, to someone. Thinking about the alternative, an exhaust valve. I can think of some good and bad things. When the valve is properly closed, the possibility of failure and allowing water in is zero, so failure rate is nil. The possibility of forgetting the valve in the closed position is perhaps 1 in 500, then the possibility of the system failing when you start the engine is probably 99%. On the KISS principle, I'd go with a flap every time.

Paige

[04 Marine]

I recently read a book dealing with the issue of a shut off valve in the exhaust system. I think it was written by Hal Roth. I believe the he positioned the shut off in the cockpit so that the inigition key could not be turned unless the handle for the shut off was in the open position.