[jclark003]

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.