Pressure transducer raw water cooling blocked

[phorvati]

On my northern lights generator, when seaweed cloggs the raw water strainer, generator still runs until high temp alarm shuts if off. By then impeller is melted due to lack of cooling.
I know flow meters might be too expensive and not so feasible, but vacuum or pressure sensor before or after the water pump">raw water pump hooked up to alarm would let me know flow is down and I would save the impeller.
In some anchorages, like this year on Nantucket, it happens daily.
I'm looking for model number and information on either pressure/vacuum sensors of flow meter that one can install in raw water line so I can review and order to try it out.
Thanks