Understanding Premature Battery Death and How To Avoid It

Thought this was a good article on the Nordhavn site...

http://www.nordhavn.com/resources/tech/battery_death.php

Jim, Sent from my iPad using Trawler

The Nordy's run at lower RPM most of the time, the article mentions it. It warns that the alternators aren't turning fast enough (most of the time) to reach their full output amps.
A change of drive pulleys could fix this easily enough- Gearing them to reach full output when the engine is at max normal cruising RPM would seem like a simple fix.
Warn the operators not to red line the engine, and there ya go.

We normally cruise around 1900 RPM.

N4712 said:

We normally cruise around 1900 RPM.

Click to expand...

Research the max RPM required to get full output from the alternators, re-ratio them to do it at, say, 2050, and your batteries would be well fed from now on. You might need to remove the drive belts for red line checks (prop sizing or whatever) but that wouldn't be necessary very often.
I imagine they don't do this at the yard due to concerns of over-speed damage done at red line.
Edit: The smaller alternator (on most Nordys) is used to charge the engine/genset starting battery, so I wouldn't mess with it.

>so the effective house battery bank capacity is actually only 510Ah, which is the amount we’ve determined necessary for this size of boat between charges.<

Perhaps the noisemaker mostly on lifestyle can operate this way over night , but for many folks the batts only get recharged 100% operating VERY long days or plugged to the power pole all night.

The last 15% takes a huge amount of Time to push back into the batts , so seldom does a boat operate from 100% to 50% . more likely its 85% to 50% .

The std wet LA batt can live with this , the AGM really need that frequent 100% charge , which is why they might not be a great choice for along shore cruising.

Trojan has a fine graph showing depth of discharge , vs number of cycles .