ok ive had this problem recently,after sailing u probably have heeled the boat quite a bit & in doing so dumped out all the water in exhaust line from the water lift back....it takes a few minutes to fill up again !! try pullins off the sea water line going into the exhaust if there is water there than just wait a minute or so till water appears at stern[after re connecting line]
Interesting. So, this would mean that the boat has always done it, but that I've become aware of it now, because I've rebuilt the pump. Classic mechanics syndrome, where a mechanic fixes one thing, and the vehicle owner suddenly becomes hyper sensitive about things that have gone on for years. Drives my brother (a mechanic) crazy!
Come to think of it, I'll usually check for flow at the dock, but seldom when I'm out, so this makes sense. I don't think the pump is the problem, as it is rebuilt (including a new shaft), and draws strongly when I go out and when I flush the system at the dock. I'll test the theory and report back. Hopefully, I won't report that I don't have the problem anymore because I have a new engine