Running the engine to charge batteries - gear for load or no gear?

[George_SD]

Hi all,
This topic came up recently with my friend (both of us have Beneteau's) who says he has been advised by the dealer to run the engine in reverse with idle over-ride at increased RPM in order to recharge the batteries when on anchor (so the engine runs, but the gearbox is not really engaged and the prop is not spinning).

I've read here that one should run the engine in reverse so that the engine is loaded and anchor is holding the boat (sets it harder, but puts load on the engine).


Both of us have Yanmars and I didn't find anything in the manual for the boat or the engine as far the recommended way or using the engine at anchor in order to recharge.

Anyone has a definitive answer or reference to a manual?

[ThereAndBack]

"Definitive answer" and things sailboat related do not go hand in hand. Even if a manual said something about it (which I doubt it will) people will disagree.

And the real answer is to buy more solar panels.

[George_SD]

Fair enough, but solar is not something I can do in a very short order before my next trip where I will need to recharge using the engine.

So the question remains

[Uncle Bob]

Originally Posted by George_SD

Hi all,
This topic came up recently with my friend (both of us have Beneteau's) who says he has been advised by the dealer to run the engine in reverse with idle over-ride at increased RPM in order to recharge the batteries when on anchor (so the engine runs, but the gearbox is not really engaged and the prop is not spinning).

I've read here that one should run the engine in reverse so that the engine is loaded and anchor is holding the boat (sets it harder, but puts load on the engine).


Both of us have Yanmars and I didn't find anything in the manual for the boat or the engine as far the recommended way or using the engine at anchor in order to recharge.

Anyone has a definitive answer or reference to a manual?

This makes absolutely no sense.

[Stu Jackson]

If you need to charge your batteries at anchor, don't risk pulling out your anchor. Your alternator alone is a "LOAD", isn't it? It's creating additional resistance and there are tons of reference material available that'll tell you how many horsepower any given alternator amp draw converts to.


Go ahead and run your engine out of gear. Also do it at more than dead idle or you won't recharge anything. I've found 1500 to 1800 rpm gets me 30A out of a 100A alternator with a 50% SoC 400 ah bank, of course it tapers off as charge continues. I run for about an hour and put back 25 or so ah.

[Sam Woodbridge]

Originally Posted by Uncle Bob

This makes absolutely no sense.

Yes and no it doesn’t make sense.

What I don’t understand is why you put your throttle in reverse bypassing the reverse gear. Why not place it in forward bypassing your forward gear for a engine rpm increase?

There was a thread about running Diesel engines without a load on them not to far back. Maybe a week ago? Everyone has a opinion, but most said there is no harm running a diesel without a load on it and that it has been debunked.

I too am doing what your doing. If I anchor out for more than a day. I’ll run the engine for a hour just to charge my house bank. I run the engine up too 1400 rpm with the gear selector in forward bypassing the forward gear. I’ll do that at least six times a month. I seriously doubt it causes any harm, but what do I know. Someone will chime in with some experience in this matter.

The only thing I would suggest and I do it. In the Yanmar manual it does state to run the engine at wide open throttle for thirty minutes for ever ten or so hours of cruising. I can’t remember off hand how they worded that. I have the 3YM30AE. 120 amp Balmar - MC 614 regulator - victron 712 battery monitor. I get about 60 amps at 1400 rpm’s

[ChrisJHC]

I recently did the RYA Diesel course and the instructor was a very experienced marine diesel mechanic.

He had no issue with running the engine under no transmission load but fully supported running it at WOT every so often (he didn’t specify and I didn’t ask) to clear out the system.

The mixing elbow, in particular, cruds up more rapidly if you mostly run the engine at low revs.

[bensolomon]

I have always run an engine for an hour in the morning and an hour in the evening when anchored for more than 24 hours, in neutral at 1500 rpm. Or, if on a long transit, motor sail for two total hours per day. I have 210 ah AGM bank (3 group 27), a balmar 100 amp alternator, and yanmar 3gmhf 1990.

The other benefit of this is hot water for Admiral's shower.

[Tomodore]

I run in reverse at 1500 rpm, next time you are at the dock try it, then stand on the dock and pull the boat forward. Not much force required unless your boat is huge. Unless your boat is a Marina queen and only anchors for lunch if you drag in reverse you will be on the beach in any real weather. I do keep an eye out in crowded anchorages since motoring in reverse can result in different spacing with my neighbors. We have great solar and wind generation but batteries are often low in the mornings and I often am net controller on local ham and SAN nets.

[Compass790]

Every diesel powered mobile welder I used to use had a sticker on it saying " do not run at no load for long periods".
I would say it depends on your alternator size relative to your engine size.
We have a 55 amp alternator & an 8hp diesel. The alternator puts out 34 amps at 1500 rpm into a nominal 225amp bank & I reckon thats ok amount of load.
The important thing AFAIK is that it gets up to operating temp reasonably fast. If we run ours unloaded it takes forever to warm up.
If you have a 45hp engine & a 55 amp alternator you wont be loading it up much & it will warm up slowly. In that case i would be tempted to put it in reverse after usual unloaded warm up time at least until it reached operating temp.
If you drag your anchor it wasnt set properly & you have found out. Have anchor alarm on.
But agree solar panels much nicer way to go

[GordMay]

FWIW: A 12V alternator will require [load your engine to] about 1 hp per 30 amps of output power.

[GoneDiving]

Originally Posted by George_SD

Hi all,
This topic came up recently with my friend (both of us have Beneteau's) who says he has been advised by the dealer to run the engine in reverse with idle over-ride at increased RPM in order to recharge the batteries when on anchor (so the engine runs, but the gearbox is not really engaged and the prop is not spinning).

Seems like a lot of faffing around for very little gain.

Originally Posted by Stu Jackson

I've found 1500 to 1800 rpm gets me 30A out of a 100A alternator with a 50% SoC 400 ah bank.

30A @ 12vdc is 360w or 10% of my $500 elcheapo generator. Put another way, every hour of mains engine wear and tear and issues from low/no load could be replaced with barely 10 minutes of Genset use.

[JC Reefer]

I have never heard of this. Even if it were true, I don’t feel the gain of actually putting the vessel in gear would be worth the long term risk of one day breaking free from an anchor.

[goboatingnow]

The advice really applies to much larger Diesel engines then in your typical sailboat. Big diesels run unloaded tend to suffer from bore glazing and polishing and then suffer loss of compression and oil blow by. They also tend to run too cool at low revs under no load.

For small sailboat engines this really doesn’t apply

[valhalla360]

This advice came from the days before cheap solar. If you live aboard and do it every day, a small alternator may not create enough load to get the motor up to full temp and burn off the carbon deposits.

But if it's only occasionally and you motor more than charge, go for it. During the motoring, the engine will get up to temp burning off any moisture and any carbon deposits before they can become problematic.

When you say put it in reverse but the transmission doesn't spin the prop...are you speaking of a single lever control where if you pull out the lever arm, it increases the RPM but never engages the transmission? If that's the case, you aren't adding a load. The transmission is staying in neutral. Otherwise, if you put it in reverse, it will spin the prop.

PS: if running in reverse at slightly over idle pulls the anchor out, you already had an anchoring problem.