If the breaker is tripping, it's either a weak breaker or the hot water heater is pulling to many amps. Put a meter in the line and see how many amps it is pulling. That will tell you if it is the breaker or the heater.
The following 1 user Likes Sans Peur's post:1 user Likes Sans Peur's post Donaldjames (11-28-2020)
is the breaker tripping right away or only after it heats up? If right away most likely there is a bad thermostat, heating element or water leaking onto connections (usually from crack in tank). Thermostat and or element are most common causes of direct short and usually can be replaced relatively easily and are almost always replaced together. Unfortunately your 43 will require you to crawl over engine and stand on your head for access. Probably easier to pull cablemaster tub out and shimmy along the outboard side of the starboard engine.
To rule out breaker you can also swap with another breaker of similar capacity (such as an ac compressor). Just make sure you disconnect shore power while moving.
The following 1 user Likes jclark003's post:1 user Likes jclark003's post Donaldjames (11-28-2020)
I had a similar situation on my motorhome and it turned out to be a shorted out heating element. I would also highly consider the breaker going bad as circuit breakers in some cases are toggled on and off quite a bit and can wear out . Best of luck and let us know what you find out .