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.

Within a given battery technology there is no practical difference
between two sixes in series and a twelve of the same capacity -- in
either case you have six two-volt cells, connected on top. With the
sixes, one connection is external, so you have to maintain two more
terminals, but you get to handle half the weight at a time when
replacing them.

Heat dissipation is a function of surface area, so I suppose if you
took two sixes and separated them by a few inches you might do a
little better. I've never heard of anyone doing this, but many larger
vessels have an exhaust fan on the battery box. The reason it's
required is to vent hydrogen, but it probably also provides cooling.

As for the logic, "if one battery goes, it is much easier and cheaper
to replace", that's BS. If you lose half a battery set, you have to
replace both -- never mix battery types, sizes, or ages in a set.

This comes down to a price and form factor decision -- whatever fits
in your available space that has the capacity and quality you need.

And, BTW, the choice isn't limited to sixes and twelves. Rolls, the
top US marine battery manufacturer, makes fours and eights (for those
of us who run 24VDC) as well as sixes and twelves.

Jim Woodward
www.mvfintry.com

(Kneafsey Mike) wrote in message . com...
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.

Everyone says it is the correct decision, but one person mentioned
that the batteries don't do well in the heat of the Caribbean due to
the inability to disapate heat while charging. One person said this
was pure BS.

Thanks,

Mike
www.sailingthecaribbean.com

There are a couple of issues here...the only truly deep cycle, reasonably
priced, flooded batteries that are readily available are 6 volt golf cart
batteries. Most so called "marine deep cycle" batteries are just truck
batteries with rope handles. The golf carts are about 62 pounds apiece so
they are generally much easier to install.

I had a house bank of 12 golf cart batteries that I took 550 amp-hrs out of
every day for a three year Eastern Caribbean cruise...they performed
flawlessly. On a $/amp-hr basis, golf cart batteries beat all comers.

Hope this helps-
Charlie