Postby km1125 » June 6th, 2021, 6:40 pm
Really, the only connection between the 12V and 115V circuits is the battery charger. Most of the stuff on the boat, with the exception of the water heater and air conditioning, runs off the 12V panel which is fed from the batteries. The batteries are recharged anytime the engines are running. If you shut EVERYTHING off on the 12V side then there'd be nothing draining the batteries and your boat could sit there for months until your next trip and would have fresh batteries to start the engines.
HOWEVER - there are some 12V circuits you don't want to shut off, particularly something like a bilge pump. Not knowing how often the bilge pump needs to run, you have no idea how long that pump could run off your batteries before it would run it completely down and then neither the bilge pump would run and the engines won't start. So most folks install a battery charger that can be connected to shore power to keep the batteries charged regardless how often the bilge pump needs to run. There might also be some other 12v circuits that you'd like to leave on too... such as a fridge to keep the drinks cold while you're away from the boat.
At the dock, you might like the convenience of hot water and air conditioning. Those circuits run off the 115 side. On a larger boat, you might also have a generator installed so you could also have 115 when you're away from the dock. On smaller boats that's just not practical.
When you fill the main (potable) water tank, that's what the potable piping is connected to and it provides hot and cold lines. There is a potable water pump in the boat somewhere that draws from the potable water tank and pressurizes the hot and cold lines. The hot line goes through the water heater before it goes to all the fixtures. Sometimes the water tank also has a heat exchanger built into it that's connected to the engine, so while the engine is running it can also heat water (just like a heater core in a car provides hot air). If you have this feature you can have hot water even though you don't have access to 115v power, like when you're out on the hook enjoying the water. If you don't have that heat exchanger feature then you'll only have hot water when you're connected to 115v shore power. Once you've filled the potable water tank, look for a breaker for the "water pump" or "potable pump". Turn that on and open some faucets to see if you get water out the hot and cold sides, THEN you can power up the water heater if you're connected to 115V shore power.
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