Mine did the same thing. My cover plate (and back plate somewhat) were scored from wear. After turning over the cover plate (clean new surface), my pump worked much better, and no longer lost it's prime - like yours.
This trick only works if you have an unpainted, un-engraved, plain flat cover plate. Many are engraved with part numbers and such.
I believe that the water rushing past the hull, while sailing, causes (Venturi effect???) which helps to pull the water inside the pump and hoses (along with back pressure from exhaust possibly) You then get air and pump has to reprime.
Have a look at cover for wear, and if so, clean up other side and flip over. I used a very thin layer RTV (auto) silicon gasket instead of the paper gasket. You want it thin so that the impeller is as close as possible to the cover plate.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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