Our boat has a small Blue Seas 8027 AC distribution panel with main two pole
breaker and 6 circuit capability.

One circuit feeds the Truecharge 10TB charger and another will feed a hot
water heater (1200watt). Others only feed outlets.

The Truecharge doesn't have an integral on-off switch . So, as with DC
panels, the breaker is used as a switch.

When I install the hot water heater, I was planning on hooking it direct to
the panel and using the breaker as the switch. But, then I seemed to recall
that breakers shouldn't be used as switches on 120V systems?

But thinking about our house that has electric baseboard heating. There are
no disconnect switches other than the thermostats and most of them have no
OFF position. The water heater will have a thermostat too!

The water heater manual shows a fuse on the heater side of a double pole
switch (switches both sides of AC). I could install a switch between the
heater and the breaker panel. But perhaps the breaker and the double pole
main disconnect switch serve the same purpose?

Then there is the charger which has no separate switch.

GBM