Might be easier than that
Looks like another chore upside down in a confined space to get at the vent hose.
You could definitely be onto something with your thoughts about a tank vent blockage. But you MIGHT not have to stand on your head in the bilge to clean it out. The most common locations for a tank vent blockage are the vent thru-hull and the connection to the tank--both that end of the vent line and the vent fitting on the tank. So the first thing to do is clean out the thru-hull...scrape it out with a screwdriver blade or whatever works. Then stick a hose nozzle up against it and back flush the vent line. With any luck, that'll clean out the other end of it.
Why would the load on the motor suddenly increase enough to trip a breaker?
If the pump can't pull anything through it, it'll cause the motor to "try harder" which causes it to overheat and pull more amps, which causes it to trip the breaker or blow a fuse.
Looks like another chore upside down in a confined space to get at the vent hose.
You could definitely be onto something with your thoughts about a tank vent blockage. But you MIGHT not have to stand on your head in the bilge to clean it out. The most common locations for a tank vent blockage are the vent thru-hull and the connection to the tank--both that end of the vent line and the vent fitting on the tank. So the first thing to do is clean out the thru-hull...scrape it out with a screwdriver blade or whatever works. Then stick a hose nozzle up against it and back flush the vent line. With any luck, that'll clean out the other end of it.
Why would the load on the motor suddenly increase enough to trip a breaker?
If the pump can't pull anything through it, it'll cause the motor to "try harder" which causes it to overheat and pull more amps, which causes it to trip the breaker or blow a fuse.