Shore Breaker on the boat keeps tripping! Help!

If the boat has a couple of refrigerators and three or more A/C units, it is difficult to reproduce the problem. The breaker might be tripping when a combination of those units start at the same time (when peak current occurs). If keeping one of the A/C units off is an option, this could be a good measure at least until this is solved.

I suggest following the recommendation of swapping breakers to figure out if it is a faulty one and/or verifying the shore power voltage. This might be a good opportunity to perform an A/C "check up" including current measurement, air flow, etc. Perhaps the frequency of the occurrence increased because here in Florida it is hot and the sea water is pretty warm, which causes A/C cycles to increase.

If the voltage drops (223 to 208) the amperage will go up, Ohms Law. Understanding electricity is all simple math. +a little thermodynamics.

First, intermittent problems are sometimes very hard to track down, A/C and fridges draw up to 30% more than RLA (running load amps)during start up. All inductive devices do, resistance loads like a electric grill or stove/oven do not. It could be as simple as two compressors try to start at the same time or a bad capacitor or a thermostat allowing a compressor to short cycle.... once a compressor shuts off it takes from 2 to 4 minutes for the pressure to equalize (high side & low side must be equal) so it can start again With out raw data, like voltage, running amp ,starting amps your giving the forum nothing to go on. If you know how to use a multimeter and amp probe and not afraid( plus have some education on working inside a hot electric panel so not to harm or kill yourself) remove panel covers to get some data for the form. Then we may be able to talk you through a fault tree, until
your problem is solved. Many tines when a intermittent problem shows up a data logger needs to be connected & left there so the electrician can analyze the data and pinpoint the source problem.

Without data everybody is just guessing.
Walt

Actually resistance loads do draw more current at startup since the resistance of a cold element is lower than the resistance of a hot element. That's why light bulbs generally burn out when first turned on, the high inrush current due to the cold filament.

But it's not 30%, . While your correct technically it's like less than 1 %. Thermal shock (High temperature rise) in nano-seconds blows them. All electrical components have a design life and thermal cycling is a big part of that calculation.

Yes, Resistance cause heat which causes higher resistance that causes more heat ,then more resistance ,higher heat until a breaker kicks or things start melting. This is especially dangerous if the connections are corroded or loose . If you ever feel a breaker, cable, plug or receptacles warm or hot, shut it off immediately. Them look for the fault. To small wire size for the current will also cause overheating.

These problems the OP has do not fix them self unless it is a low voltage problem . I seen marinas have 400 amp 3 phase power installed ,but once the 2 high legs get loaded to capacity they start supplying power from the low leg which is normally around 208 volts phase to phase instead of the normal 240 volts.
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Short of a car hitting a telephone pole and the 12,000 volt lines ending laying on the 240 volt lines I seen very few power surges. The most common is low voltage (brown outs) that destroy equipment. Electronics are especially sensitive to low voltage.

I know Miami Beach Marina well and 208 volts is very common there during the summer. It's a combination of the low voltage, dirty chiller coils (drawing more juice) and the summer heat. Having an ac tech clean the chiller coils might fix the issue entirely as will shutting down a few items on the boat, and if that doesn't work get a step up transformer.