Westerbeke BTD 8.0 KW Raw Water Flow Issue

[Bob Hiller]

Generator has ample water flow through water pump">raw water pump while 41 SCA is not underway. Once underway pump becomes (air bound) and sea water flow through system is lost. Resulting in overheating shut down and the raw water pump impeller burns up. Last time out was lucky and wife caught generator heating up and shut down. Half an hour later started her up but no water flow through pump, pulled cover plate and all fins intact (no water however). Filled housing with impeller grease and started her up, ran fine pumped water while dead in water. Back ground, never changed Maxum installation design inspected all hoses (some replaced) never changed lengths and lightly drilled out pickup strainer cover before through hull. Replaced the impeller too many times to count. Cant tell you if previous owner had the same issue. Help, as my wife loves her AC. Bob

[tkeithlu]

What sort of strainer is at the bottom under the hull? I had a similar problem when the strainer faced aft, such that there was a vacuum on the raw water feed rather than pressure when underway. A few minutes with a grinder converted the strainer to "neutral," with slots that covered the complete dome.

You also might have an air leak into the system between the hull and the pump. Check for loose hose clamps or a split hose.

[PJHoffnet]

4100 SCA owner w/same genny. Never ran the genny when underway making way, only in a slip or at anchor, because I did not believe I could guarantee adequate raw water intake.

Looking at the genny raw water pick up (which I'll assume is the same as yours - just fwd of the port engine intake) it is significantly smaller and lacks the 'forward facing scope intake form that the engine raw water intake has. In my mind, that would make it much more prone to air binding when there is flow going across it - especially when on plane.

I've attached an image of the genny and the port engine raw water intakes. Image was as we were hauling out to redo the bottom.