It's a Perkins 4-236 in a 51'Beneteau. A friend calls me over and says his engine won't turn over. I get there and try to crank it and can hear the pistons trying to squeeze water out. We pull the injectors out and find cyls #2 and #4 full of raw seawater. We remove the exhaust tube from the elbow and find the entire exhaust system is completely full of water. Now, even though the engine and the exhaust system are below the waterline, the exhaust outlet at the transom is about 18" above the waterline. the outlet could never get underwater,except in some serious following seas, which this boat has probably never seen. So, I've been racking my brain trying to figure out how the exhaust got so full of water to actually back up into the engine and fill the cylinders full of water. The exhaust is pretty simple, from the elbow there's about 3 feet of tube that goes to a (muffler?) box, then another tube goes from there about another 20' straight out thru the transom. I guess my questions about this system are: 25 feet of exhaust seems like it would take quite a bit of exhaust pressure to push that much water out thru the transom. Has anyone heard of an exhaust system being too long for the engine? The raw water pump looks like it's part of the engine (gear driven) Has anyone heard of a raw water pump pumping TOO much water? It's kinda hard to tell exactly, but it looks as if the exhaust outlet at the transom is actually higher than the exhaust elbow, I would think that if that's the case, then all the water that's in the exhaust when the engine shuts down has free reign to slosh around in there, even to back up thru the exhaust valves into the cylinders. Has anyone heard of this inherent design flaw in the Beneteaus that would cause this concern? All thoughts and comments appreciated, David Mullenax, San Diego
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Two Thoughts, David
1. Cranking the engine. Did anyone crank the engine for over a ten second interval without shutting off the intake? Most likely culprit. That pump moves more water than most prople think. 2. Water hammer. I know someone who was at a very rolly mooring. The whipsawing of the boat caused water to 'hammer' up through the system into the cylinders.
1. Cranking the engine. Did anyone crank the engine for over a ten second interval without shutting off the intake? Most likely culprit. That pump moves more water than most prople think. 2. Water hammer. I know someone who was at a very rolly mooring. The whipsawing of the boat caused water to 'hammer' up through the system into the cylinders.
Cruising World jan03
Don't know why this happened but it sounds similar to the account of HAWK in the Jan '03 edition of Cruising World. Evans didn't figure out how it happened, but he installed a "huge valve" in the exhaust hose and reported no trouble since.
Don't know why this happened but it sounds similar to the account of HAWK in the Jan '03 edition of Cruising World. Evans didn't figure out how it happened, but he installed a "huge valve" in the exhaust hose and reported no trouble since.
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