Big engines and extended slow running

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ivorufo

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Apologies if this has been asked before:

Is it wise to run 150-250 hp turbo diesels fitted to Merry Fisher/Antares type semi displacement craft at low revs/load for extended periods such as on inland waterways?


Thanks
 
Breaks out the popcorn and sits back for a heated debate. Some will tell you you run the risk of glazing the bores, poor combustion and resultant contaminants in the oil. I think the first is a bit of a myth, the second has legs, but I'd imagine the most harm would probably come if after years at such loads you suddenly decided to change tack and give it full welly 90% of the time by going to sea. But it's all supposition on my part with no corroborating evidence....?
 
I believe the popular "glazing bores" argument is only valid if the engines are run at high revs with no load. Running a big turbo-diesel slowly is more about running inefficiently at low revs and producing carbon which can, over time, clag up your turbo and cause excessive deposits elsewhere. Giving it "full welly" after a period of such running is exactly what you should do actually. Diesels like to work and often a period of high load will act as a tonic and blast the crap out of it! So if like me you are contemplating the French canals to get you to the Med, give it welly across the channel and up the Seine and when you get through to the Med do the same. The bit in the middle should not cause problems then.....
 
Cox Engineering have a useful page about bore glazing. The summary is shown below, and I think the bit in bold is most relevant to the OP's question

A fully run-in engine is unlikely to suffer bore glazing, provided that its sump is filled with the recommended lubricant. Piston rings in an engine that has run for about 100 hours will conform well to the bores, limiting blow-by and oil consumption. An engine with less than these hours should never be run at light load for long periods, as is typically done for yacht battery charging. In the middle part of its life, glazing is less likely while the bores remain in good condition, although as wear increases its likelihood will increase. However, bore polishing is always a possibility with light loading. The solution is always to load the engine when battery charging, by driving the propeller. An engine that is driving the boat will never suffer from either glazing or polishing, even if it is at anchor or on a mooring.

The page is here: http://coxengineering.sharepoint.com/Pages/Boreglazing.aspx
 
Another option would be to fit a secondary (10hp or as appropriate) outboard on a drop down bracket. Amazing as it may seem, 10 hp will drive a 23 - 25 ft boat at 4 - 5 knots.

It is a common idea on recreational fishing boats, to be used for low speed trolling or as an emergency limp home back up.

They can be rigged to work of the main steering and have a remote throttle control.
 
The English Channel swimming boats spend all summer back and forth at idle, sometimes up to 30 hours at a time without a rest or a clear out. I know a couple of the skippers and not heard of any obvious issues.
I do the same with my twin 300 Perkins, maybe they smoke a bit more than they used to but that could be anything, I don't worry about it.
 
Again... no scientific evidence, but I would think the turbo would suffer....... not running at design temps and speeds could cause some issues later down the line. Wastegates spring to mind.
 
Not sure what engines you're asking about but I've got a pair of Yanmar 350hp turbo diesels and the manuals say no issues with slow running. In fact, many Brooms like mine spend most of their like pottering up and down rivers and no one in the owners club has ever reported problems as a result of doing so.
 
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