My preference is for the master switch to turn absolutely everything off. Including the starter and alternator
This helps with maintenance
: to easily de-energise the engine
while you are working on it. For example, the four cylinder Yanmar's have the starter connections right where your hand wants to be when changing the raw water
impeller. On another engine
I've had, the dipstick had a tendency to short out on the back of the alternator.
But most important, a boat
has burned to the waterline because a wire to the engine shorted out. The folks on board were not able to quickly cut power to it, so even though they extinguished the fire, it kept flaring back up. So, I feel it's important, if you smell smoke, for one switch to turn everything off. Which is why I believe in having a large fuse, either between the batteries
and the switch, the switch and the starter and alternator, or both.
However, your configuration has the advantage of never being able to blow the alternator by selecting 'off' while the engine is running.
Connecting the starter and alternator through the master switch also allows you to only use the house bank to start the engine. I prefer that flexibility. If for some reason the starter bank is super low, I dislike the only option being 'combine', which will have the house bank charging
the starter bank while you are trying to crank the engine.
I am probably in the minority, but for many of the same reasons I don't like automatic combiner switches. I think one loses flexibility for the small convenience gained. If there is a problem with the house bank, I prefer being able to run the VHF
, and etc from the engine bank, and be able to charge it without the combiner kicking in.