Good evening , starting battery question . I have a 34 main ship 200 perkins . I'm not new to Diesels or batteries , just this engine . Have always used big 8 d's . But seen discussions here about 31 's and also two 6 's to make the 12 because easier to move than the 8 d's . This will be a cranking battery only , any recommendations ?
As I recall... which, of course may be faulty...
We had a single 8D in our Mk III with DD 8.2T, acting as dual-purpose starting and house battery, and it was located to starboard, underneath the saloon sole, not all that easy to reach and service.
If we still had that boat today, I believe I'd consider a couple options, somewhat combinable, and in no particular priority order (yet):
a) Change to AGMs, to alleviate that whole service thing.
b) Separate start and house functions. A single Odyssey PC-2150 (huge cranking amps) would make a fine starter. A group of 4x or 6x Lifeline 6V AGMs should make a fine house bank. (I can't remember how much space was available.)
c) Leave the bank as dual-purpose, and create a single bank of 4x or 6x 6V AGMs (~440 or ~660 Ah); the combined cranking amps would be way more than sufficient to start the engine.
d) Leave the bank as dual-purpose, but create a single bank of 3x or 4x G31 12V batteries, whatever will fit (3x = ~ 300Ah, 4x = ~400 Ah). In this case, Odyssey could be good (our experience in our current boat has been very positive) or maybe Firefly Oasis Carbon Foam AGMs could be worth a look... especially if anchoring out a lot and for longer periods. (The taller Odyssey batteries could be great too, but one reason I'd home in on G31s is about the weight of each individual battery... and what it takes to get it into the installation.)
In terms of effort -- both for installation and for follow-on service -- I suspect a combination of a and c or a and d would be easiest.
-Chris