Engine raw water pump air lock on CR42

[s/v Patty Jean]

For the third time in 9 years I have experienced an air lock problem after launching off a significant wave at an inlet, not a great time to lose your engine.

Fortunately this time I had installed a Globe run dry impeller (blue one, given to me by our sister ship Sea Clearly), they are the expensive ones, but so is my boat. and after sailing through Little Farmers Cut on a flood tide I turned the corner and dropped the hook in a safe anchorage. I had to run the engine for a few minutes and when I inspected the impeller it was in perfect condition. The previous time the black rubber impeller lost every lobe. has anyone else in Cabo Rico land ever experience this and have you come up with a solution? I was thinking about installing an air vent in the top of the raw water inlet hose or possibly in the top of the raw water strainer.

Thanks

Cabo Jim 

 

[Thierry Danz]

Jim,

I have never had the problem you describe in 14 years of ownership of my CR42. Perhaps your installation is different than the one on my boat. Unless I understand you incorrectly, I certainly would NOT install a vent anywhere in the raw water hose. That would add an air intake into the raw water supply and would exacerbate the problem. I do replace the impeller more frequently than the 600 hours the manual specifies. In my experience they do not last that long. Are you sure there is no partial blockage in the intake thru-hull? Or a loop in the intake hose that extends above the waterline? On my boat the intake seacock is under the sink and the hose goes pretty much strait to the strainer under the settee and thence to the raw water pump on the engine.

At one time I considered changing to a Globe impeller. When I mentioned that to a friend of mine, who used to be an associate editor of Practical Sailor, he recommended against it. He said that they will run longer than a neoprene impeller when dry, but eventually they do fail, and then they fail catastrophically, in tiny little pieces. Much more difficult to locate than the blades of a traditional impeller.

Last year I installed an exhaust temprature alarm (Borel). That should go off long before the engine overheating alarm is triggered when the cooling water is interrupted.

Thierry

CR42#12 CURLEW

Baltimore, MD

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[s/v Patty Jean]

Hi Thierry,

It sounds like my raw water intake is the same setup as yours, so that makes it even more perplexing. Also it seems to only happen in step seas with significant waves. Whenever I haul the boat the raw water pump always primes with no problem when I put her back in the water.  Regarding the air vent solution, it is common practice to install them on piping systems on industrial heating/cooling systems that use positive displacement pumps for circulation, it would be a challenge to find a location where it would fit. I know the more things to add the higher the probability for failure. {eg. check valves on bilge pumps}. Regarding Globe run dry impellers, I have only ever had a catastrophic failure of an impeller with the standard black impellers (again due it running dry). Unless I find a solution to the air lock problem, I think I will stay with the Globe run dry type and change it on a regular basis. I like your idea of an exhaust temperature sensor and alarm.

Jim

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[Clay]

Dumb question..but what about a possible leak in or around the raw water filter or connections?