chsjohn...many cruisers will spend a lot of time on the hook just charging batteries if they don't have alternatives to their engine. We've had several discussions debating the damage this can do and comparing to truck diesels which idle for long hours without apparent harm. I wrote BoatUS and boat system guru Don Casey on this issue and here is what he told me:
"Diesel trucks idling in a Dakota truck stop have no implication for a 40-horse diesel powering nothing more than a 12-volt alternator. For one thing, the idle time in the truck is between long and continuous hours of the engine operating at full power. If you run your engine at near full throttle for 10 hours, then let it idle for 6, then wring it out again for 10, the idle time will indeed have little if any impact. That is not what we are talking about. In the case of a boat diesel used for charging the batteries, you fire it up each day just to let it tick over at a fast idle for an hour or two, then shut it off. And you do that again tomorrow and the next day and the day after that. The engine runs too cool for complete combustion, resulting in inevitable carbon build-up inside the engine and the exhaust system. Equally destructive, warming the engine attracts moisture into the crankcase but the idling engine never gets hot enough to drive this accumulating moisture out of the lubricating oil. The result is corrosion of the bearing surfaces. Every diesel manufacturer will tell you that unrelieved light loads are murder on their engines. Today you will find very few long-term cruisers depending on the main engine as the primary source of electrical power. The advantage of solar panels and wind generators is not just lower fuel costs. They reserve engine hours for propelling the boat, making a good-quality diesel engine in a sailboat almost immortal."
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