Running engine without alternater

[Kwik Decision]

But my main question is, is it normal for alternators to just snap like this? It's only two seasons old. Is this just the sort of thing that happens from time to time, it could it be my engine's way of telling me about a more profound problem?

No, it's not normal for an alternator belt to just fail, unless it's very old. I replaced ours a few years ago, at about 12 yrs old, as a precaution. The old belt still looked, and was working fine...

I'd be having a good look to try and work out why the 2 yr old one failed. Was it correctly aligned, and tight?

 

[Captain Sillyboxes]

It might've been slightly undertensioned but not drastically so

 

[billskip]

It might've been slightly undertensioned but not drastically so

If the alternator is under high load it could slip and generate heat, the belt could fail fair quick.

 

[Captain Sillyboxes]

One thing about it is I'd been running for hours at recommended cruising revs of 2,700 RPM and then to get into port against the tide I'd pushed it to full revs about 10 minutes earlier. Perhaps it was a bit undertensioned and this was what put it over the edge?

 

[Stemar]

I don't think I've ever had a "fan belt" snap in over 50 years of driving and 20 sailing. I would guess that the belt had a fault of some kind, though it would be worth checking the alignment of the pulleys.

 

[billskip]

I don't think I've ever had a "fan belt" snap in over 50 years of driving and 20 sailing.

You obviously carried a spare....oh, and the tights can be a tad difficult, especially when they are fairly shredded when trying to rip them off reluctant crew.....

 

[Stemar]

You obviously carried a spare....oh, and the tights can be a tad difficult, especially when they are fairly shredded when trying to rip them off reluctant crew.....

Yep It's a well-known fact that belts only give grief when you haven't got a spare.

 

[Sandy]

Last weekend I ran my engine (yanmar 2YM15) for 11 hours continually as we crossed Lyme Bay in flat calm conditions. Just as we were coming into port it started making the continual high electronic beep it does when it is unhappy and all the warning lights came on.

I switched it off, dropped the anchor, had a look and saw that the alternator belt was broken. To my shame I was not carrying a spare but luckily I managed to get a tow in.

On this engine, the belt that drives the alternator doesn't drive anything else so according to this thread, once I'd ascertained the cause of the problem I guess I could've ignored the warning sound and lights and completed the trip under my own steam.

But my main question is, is it normal for alternators to just snap like this? It's only two seasons old. Is this just the sort of thing that happens from time to time, it could it be my engine's way of telling me about a more profound problem?

The belt is there to drive the alternator thus generating electrical power. In theory running the engine with a snapped belt should be OK, but you mention that was a 'continual high electronic beep it does when it is unhappy and all the warning lights came on'. Personally, I'd be wanting to know why the beeps were being made before running without the alternator.

Belts do snap, like us they age. Last time it happened to me was just after I got on the 0000 to 0300 watch off Ouessant, you know the place big jaggy rocks and more lighthouses than you can shake a stick at, after crossing from A Coruña. The whole crew was wide awake in about eight nano seconds. While they peered at the engine, I checked that water was coming out the exhaust - it was.

With two sets of eyes looking horizontally at the engine they could see no problems. I was looking vertically down from the companionway and spotted the belt in the bilge - problem identified.

It came as a surprise to find not one, but three spare! Clearly, this had happened before.

 

[dukeofted]

If the belt is only driving the alternator then you can safely run the engine without the belt, the engine doesn't require electrical power to run once started. You could turn the ignition switch off to silence the alarm but then you wouldn't be warned if the water temp got too high or the oil pressure too low.

 

[VicS]

Hi I thought I'd resurrect this thread instead of starting a new one. Last weekend I ran my engine (yanmar 2YM15) for 11 hours continually as we crossed Lyme Bay in flat calm conditions. Just as we were coming into port it started making the continual high electronic beep it does when it is unhappy and all the warning lights came on.

I switched it off, dropped the anchor, had a look and saw that the alternator belt was broken. To my shame I was not carrying a spare but luckily I managed to get a tow in.

On this engine, the belt that drives the alternator doesn't drive anything else so according to this thread, once I'd ascertained the cause of the problem I guess I could've ignored the warning sound and lights and completed the trip under my own steam.

But my main question is, is it normal for alternators to just snap like this? It's only two seasons old. Is this just the sort of thing that happens from time to time, it could it be my engine's way of telling me about a more profound problem?

Puzzled on two counts

Firstly I'd expect a broken alternator belt to result in the "no charge" warning light to come on alone without sounding the audible alarm.

Secondly according to the diagrams in the owners manual the alternator drive belt also drives the freshwater coolant pump. ( the raw water pump is driven by a second belt)

The no charge warning light could easily be missed bur eventually, if the coolant pump is not being driven, the coolant high temperature warning would be triggered and the audible alarm should then sound.

Attached the schematic of the warning lights ( #8 is the "no charge" warning light, #5, #6 and #7 are the low oil pressure, high coolant temperature, and water in sail drive warning lights #4 is the audible alarm and #41 are the diodes which drive the audible alarm ) and a diagram of the alternator/coolant pump drive belt layout

( when fitting the new belt a strong thumb pressure at point A should deflect the belt by 8 to 10 mm)