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Problems running the engine whilst moored up so as to charge the batteries.

Referring to Graham Booth's article "A Sunny Solution" (p.48 WW Nov 2012), he warns about glazing the cylinder bores if the engine is run to recharge the batteries.
I was concerned about this potential problem, which many people seek to minimise by running the engine with the prop engaged, so asked Beta Marine about my own 1994 BV2203, which is a 50hp four cylinder Kubota diesel. Their advice was to run the engine at about 1200 rpm without engaging the prop. Their technical guy stated that they had had no trouble with glazed bores.
Since this question seems to crop up quite often please could the sages at Waterways World provide a definitive answer?

Asked by: Colin Wilks  | 6.05pm, Monday 8 October


WW says:

Generally the advice from most manufacturers is not to run the engine without significant load, as this can cause wear- as often stated in engine handbooks. Older engines tend to be more tolerant of this, but sometimes engines do not become hot enough to remove deposits, or the oil sump remains fairly cool, which can lead to sludge forming earlier than normal in the oils lifetime.
Many modern diesels fitted to boats have such large alternators fitted that, given a large battery bank to charge, this might be considered as a significant load! A 170 amp alternator, running at half capacity would take around 2kW of power from the engine- possibly more.
If the manufacturer is happy for you to run the engine in this way, then it is fine. However, I have come across quite a few engines, often on residential boats, that smoke a lot and show signs of premature ageing, due to being run off-load for long periods- or, even worse, only run for less than an hour at a time, which doesn't allow the whole engine to warm up properly.
Some engines are better than others in tolerating off-load running; others can glaze bores, as Graham points out, while some soot up the valve seats and exhaust outlet- often noticed by thick black smoke and soot when they are put under load!
Charging batteries by running off-load is also not an efficient way to produce electricity; and it also increases pollution- and can annoy the hell out of others moored nearby if it is done often!

Mark Langley  | 8.06PM, Monday 8 October

Some years ago, I did a quick survey of engine manufacturers at an IWA Festival to discover their feelings about off-load engine running. As I recall, Beta Marine was the only one that did not discourage the practice. Some thought it was better not to - especially if the engine had not been fully run in - while others strongly disapproved.
It seems, unfortunately, that there is no definitive answer to this question.

Graham Booth  | 8.54PM, Monday 8 October

Colin, I wear my anorak with pride!
Going for a trip out is always good anyway, however short! The water always heats up quicker that way anyway...

Mark Langley  | 11.23PM, Monday 8 October


Readers say:

Looking at the timing of our posts, I suspect we should plead guilty to being sad old anoraks, each post being made when most sensible boaters are either in the pub or enjoying a tranquil glass on the back of the boat whilst watching the stars!
It occurs to me that an absence of definitive answers is actually one of the many charms of boating, so, on reflection, I'll run the engine when moored only if it's essential, and try to charge the batteries by actually going somewhere, even if it's only there and back to the nearest winding hole.

Colin Wilks  | 9.29PM, Monday 8 October

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