Kneafsey Mike wrote:

We are presently having a new boat built in South Africa. It has been
recommended that we use Trojan 6v rather than 12v for our house
system. The logic is that if one battery goes, it is much easier and
cheaper to replace. ...

RVrs argue this endlessly. Dunno about So Africa but in the US 12V
batteries are so much more common that they cost little, if any, more
than 6V batteries and are easier to deal with. Also, rumor abounds that
new electricty-eating cars will soon go to 24 or 48V systems for the
same reasons we went from 6 to 12V 50 years ago: less current = thinner
wire for same watts.