Charging batteries with engine while sailing

[brokesailor]

I am not sure if this forum is the best place but here it goes. I recently crewed on a delivery to St. Maarten. Right off the gate the boat generator that is used to charge the batteries malfunctioned so we had to use the enine to charge. With no lack of wind we were sailing at hull speed on a screaming run. The owner would charge the batteries with the engine in neutral with rpm's slightly above idle.
I mentioned that running a diesel engine "unloaded" was not good for the long term health of the engine but he replied that he was worried about running the engine in gear and the effect that the water going past the prop at hull speed basically driving the engine.
Any thoughts?

[jameswilson29]

Yes, why doesn't he have solar panels?

[brokesailor]

Well that's totally off the subject but its a classic Hinckley 48 yawl that he doesn't want to ruin its classic lines.

[SimonV]

I do it myself when necessary, if the batteries are low charging them like this is no biggie as driving the alternator to bring the bats to @ 80% loads the motor by about 3 or 4 HP.

[jameswilson29]

Originally Posted by brokesailor

Well that's totally off the subject but its a classic Hinckley 48 yawl that he doesn't want to ruin its classic lines.

That's called big picture thinking - solving a problem by avoiding the existence of the problem in the first place.

It is foolish to go offshore in a boat without redundant systems. Relying entirely on the engine to charge the batteries is foolish.

I would be careful about crewing for someone whose greatest concern is the appearance of the boat.

[floridajaxsailor]

Seems logical to me but you are right about engine health...
it would seem silly to run the motor more than say 10 minutes- I find mine charge in far less time but 80 percent of the people you talk to will tell you to keep the engine running for half an hour which is ridiculous
& a waste of fuel
Another story of anxiety ruling the day, as if u are on a broad reach w fair winds:
compass, candles & healthy men(physically)
everything you needed to get through the day
& night
happy sailing
-JD

[jrd22]

Running the engine in neutral while charging the batteries isn't going to hurt the engine. Actually, it seems to me that there is a lot of paranoia amongst sailboat owners about harming the engine if they don't run it hard enough, which may have some validity over several hundred or thousands of hours, but a couple of hours to charge the batteries is no big deal. As long as the engine gets run on a regular basis at cruise rpm and normal operating temperature, and assuming the engine is in good mechanical condition, it won't bother it at all to charge the banks. Note: it might take several hours to fully charge the bank depending on size of alt. and number of batteries and % discharged.

@James- I would be careful of anyone that would destroy the lines of a classic H48 by putting a solar arch on it:-)) Oh, and they had redundant systems, the generator quit on them.

[73Morgan]

Originally Posted by floridajaxsailor

Seems logical to me but you are right about engine health...
it would seem silly to run the motor more than say 10 minutes- I find mine charge in far less time but 80 percent of the people you talk to will tell you to keep the engine running for half an hour which is ridiculous
& a waste of fuel
Another story of anxiety ruling the day, as if u are on a broad reach w fair winds:
compass, candles & healthy men(physically)
everything you needed to get through the day
& night
happy sailing
-JD

10 minutes will give the batteries a decent charge. However, there are 2 things you should consider, battery health and engine health. Batteries last longer when maintained at full charge. Cylinder walls glaze over on short run times, which results in loss of compression. The engine needs to reach full operating temperatures for a decent amount of time for best health.

I would definitely agree that using the boat engine to charge your batteries is not a good idea.

[MarkofSeaLife]

I have asked a number of Yanmar mechanics and they all say its drivel. But to be on the safe side of polishing the cylinders run a couple of revs above idle. So in neutral it would normally be 800 rpm I run at 1,200. Rpm and every few hours race the engine like it says in the operators handbook.


Mark

[FarCry]

Originally Posted by 73Morgan

10 minutes will give the batteries a decent charge. However, there are 2 things you should consider, battery health and engine health. Batteries last longer when maintained at full charge. Cylinder walls glaze over on short run times, which results in loss of compression. The engine needs to reach full operating temperatures for a decent amount of time for best health.

I would definitely agree that using the boat engine to charge your batteries is not a good idea.

I'm not following your math where you state that 10 minutes will give the batteries a decent charge. Assuming one is getting 100 amps (amp hours) to the batteries via a decent alternator, it seems that less than 17 amps are actually getting to the battery bank in ten minutes. Not knowing what size this hypothetical battery bank is, it's hard for me to believe that putting so little power in achieves much of anything.