AC unit raw water supply....
We have found that loss of a prime to the heat exchanger pump is not a function of plumbing in a rough seaway. It happens most often when we are beating into square seas at relative high SOW (say above 9 knots +) and occasionally getting some (as they say in skiing,) "air".
The AC pumps are not positive displacement pumps and eventually we "shake-out" the water between the pump and the raw water strainer. In my opinion, having a scoop facing forward on THAT intake (which is NOT the intake for either the engine or the head intakes) promotes maintaining the prime in the line.
As I said, we don't have scoops on any other raw water intakes. We also have robust and accessible strainers that we can inspect and clean on all but one head intake supply.
In the Chesapeake, nettles are the issue with the generator (and, if we used the main engine for charging while at anchor). In Southern New England (and occasionally, in Northern New England) we have issues with eel grass.
Newport Harbor was our worst case one summer. We kept having to clean the generator strainer while charging the batteries because it would get clogged-up. I have a 2' long heavy-duty plastic wire-tie that I use to route the short hose to the strainer that runs vertically to the sea cock below. We've had "clumps" of it occasionally occlude a generator intake -- that seemed to sucked-up against the hull. I found that turning the main engine on, putting the prop in reverse and forward seemed to clear those. I never had to go diving to clear an intake from eel grass. :^))).
You certainly need to check those strainers though! Our generator is a small 7.6 KW constant rpm Westerbeke. It really can get by with some occlusion to the flow of coolant -- until it CAN'T. The Yanmar at low RPM is more tolerant, but if you try to go at 2,500 RPM or higher, it really likes a clean intake.
The nettles in the Chesapeake are a pain in the Summer from South of the Bay Bridge through mid-July through a bit after Labor Day. Some Summers, they make the Air Conditioning a sometimes thing. I learned to change impellers on the generator relatively well by necessity. We carry about four or five extra generator impellers. We only have one- or two- for the Yanmar main engine. I've never had to change a Yanmar impeller except as routine maintenance. (That's good because the positioning of the water pump was designed for someone that more dexterity with their wrists, fingers, and elbows than I do -- and can tolerate getting their fingers and hands "burned" by a hot engine.)
