For those who don't follow the sailboatowners.com forum, I thought I'd give a heads-up on a problem I encountered. I recently changed the impeller on my raw water pump. After doing so, I found that there was no raw water flow out the boat. I spent some five hours trying to track down the source of the problem. This included snaking out different hoses, etc. What made it confusing was that the pump was pumping water. What I eventually found was that it was pumping water, but without sufficient pressure and that the cause was that there was a build-up of crud on the plate behind the impeller - a ring maybe 1/64 inch thick (if that much) right behind the ends of the fins of the impeller. This must have prevented the impeller from sealing up properly. When I scraped it off, the problem was solved.

So maybe this will help somebody else from turning a half hour job into a five hour one.