"Jeff" wrote in message
. ..
Larry wrote:
The truth is that many cruisers have over 400 Amp-Hours of batteries. My
boat, for example, was designed to carry 4 6V golf carts (Trojan T-105s),
for about 450 AH as the house bank, or 520 AH if I use the oversized
T-145. A pair of 8D's will be in the same range.

I frequently charge with a 110 Amp Balmar and it puts out 105 Amps when
started, and it stays up of 90 Amps for quite some time. I usually charge
when the bank is down 200 AH, and bring it up 120 AH, so I'm running for
roughly 90 minutes. If I used a smaller alternator, or a less aggressive
regulator, that time would go up 10 or 15 minutes. While this might seem
like a small thing, after running for over 90 minutes one starts thinking
the saving 15 minutes might be worth some real money.

These aren't made up numbers; I've been doing this for about 6 weeks every
summer for the last 8 years, and with a similar but smaller setup on my
previous boat for 8 years before that. Lest you claim that the high
charge rate is cooking the batteries, there might be some truth, but my
first set of Trojans lasted 6 years, and might have gone longer except
illness prevented me from giving them proper care one winter. Since the
Trojans are cheap ($70 each) this is not a big deal.

There's absolutely no reason why the OP shouldn't use a 100 Amp
alternator, assuming he has a large enough bank.

Essie has a Model 20 Universal (5416) 16hp Diesel, fitted with a 50 Amp
alternator. The biggest alternator I can put on this engine, according to my
research, is an 80 Amp. When I install my new batteries this year, I'll have
375 ah aboard, being charged by that small alternator and supplimented by my
two 35 watt solar panels. I have no illusions that I will be able to
fully-charge that bank with my onboard charging capabilities -- my aim is to
set out with as much amp-hours as I can get so that I don't draw-down my
batteries as much as I would if they were smaller. Back in the slip, the 50
Amp shorepower charger can complete the job. The 80 Amp alternator, if I fit
it, will be close to 25% of bank capacity, but not quite. The 50 Amp
alternator is only 15.5% of capacity, which will probably prompt me to go
ahead and upgrade the alternator. But that's not exactly cheap.