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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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  #1  
Old 10-25-2010
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Charging the batteries by running the diesel...

I've got a Westerbeke 30 diesel engine (a 4 cylinder 25 hp engine based on the old 2.2 Leyman London taxi engine). Normally, while sailing offshore, the batteries get topped up just fine as I use my engine for motor-sailing at least a couple hours a day to charge batteries while in gear.

But at anchor during weeks of cloudy days, I need to run the engine to charge my banks of deep cycle batteries. I am wondering if the belts for the alternator and saltwater pump create enough of a "load" on the engine while running in neutral? I've heard, as most others have heard, that it is not good to run the engine for long periods in neutral, but I wonder why not...since 18 wheel tractor-trailors run their engines in neutral ALL night long while pulled over. There's no load on their engines, either.

How bad is it to run the engine in neutral? What specific damage does it do? It seems as long as your bottom end bolts are nice and tight, I can't perceive any obvious areas of wear due to lack of opposing force on the crank.

The only decent way I can think of putting load on the system without burning up the propshaft, would be to have some sort of adjustable shaft-brake on the outside portion of the shaft before the propellor, where it can be cooled by seawater...and you'd have to dive down and remove the prop every time!!!!
Or tie-up between two moorings or pilings and run the engine in drive.

Any thoughts on this conundrum?
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Last edited by SoulVoyage; 10-25-2010 at 05:07 AM.
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Old 10-25-2010
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As I understand it, it is a question of glazing the cylinder walls as a result of low load, and then oil use, low compression etc. Everything I have ever read says run these engines hard, 80 % max rated rpm, or suffer the consequences.
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Old 10-25-2010
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I have looked into this a bit more for motoring at less than 80% for long periods at a time. It seems the damage of running at low rpm's can be reversed by running at full load for something like 10 min. So I would think idling the engine does no real damage if you end up motoring often enough to load it up properly.

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Old 10-25-2010
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Soul,
I had a commercial salmon troller with a Detroit Diesel, aka "Jimmie", used to troll for hours on end with no problems. Lots of theories on this issue but I think as long as the engine is run hard after trolling it should be OK. lots of commercial boats with 2 and 4 stroke diesels out there doing the same thing for many years.
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Old 10-25-2010
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While charging at the dock put it in gear. Everybody I know does.
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Old 10-30-2010
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Interesting...thanks Soulvoyage for the question. To add another question to this...

I have the ability to increase my RPM's without putting the engine into gear. Will this have the same effect as having it in gear or is there still not enough load on the engine to prevent this glazing on the cylinder walls?

SG
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Old 10-30-2010
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According to the theories, it's precisely that situation that can lead to 'glazing'.. ie high rpm without serious work load. Charging at low rpms is counterproductive since the alternator output is generally speed related.

Running in gear against the dock lines is definitely a decent load.
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Thanks,

That is what I thought....So what you are saying it is best to pull the anchor and go for a cruise to recharge the battery then to sit.

Cheers,
SG
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Old 10-30-2010
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Glazing on the cylinder walls, and building up coke (unburned carbon residue) in the exhaust elbow.

Diesels don't like to be run without load, but some modern diesels are apparently built differently to tolerate this. Bear in mind that when a trucker runs his engine all night, that is NOT BY CHOICE. He needs the cabin heater or air conditioner, he needs to know the truck will start up in the morning. That outweighs any other consideration.

Kinda like using your main engine instead of a Honda genset to charge the house bank. :-)
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I think the problem on a boat is that the engine may never get much of a workout. Charging the batteries in neutral and running for a very short time to get out of the harbor aren't much different sometimes. The trucker may idle all night but he will run under a good load all the next day. If the sailboat gets a good run that might make a difference but most don't often. And as Faster posted idle will not charge much, you need higher rpm to accomplish anything.
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