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Subject: TWL: Re: Re: Cruising range of passagemakers
From: Alex Hirsekorn (alexh@XXX.XXX)
Date: Mon Dec 31 2001 - 00:22:08 EST
----- Original Message -----
From: "Leland W. Robinson" <leland.w.robinson@XXX.XXX>
> 2) whether running my
> engine at such low loads for a long period of time
> might be harmful. Any thoughts on my second concern
> would be helpful.
>
> I believe this topic has been discussed on the list
> before. My memory may be faulty, but I seem to
> recall conflicting opinions.
Hi Leland,
A given engine is intended to be run at some predetermined level of load and
speed. It follows that the engine will be happiest if it is run that way.
The application that ignores that rule of thumb the most is the (sometimes
grossly oversized) genset. A genset's throttle mechanism is designed to keep
the engine at a specific speed regardless of load. That sometimes (often?)
results in the engine being run at high speed with very low load and that,
in turn, has been identified as very harmful to the engine.
Having said all that, the propulsion engine is a whole different kettle of
fish. Assuming you don't have a controllable pitch propeller, engine load
and engine speed are going to be quite closely related. That makes it pretty
unlikely that you'll get into the sort of operating parameters that will be
harmful. In addition, the conventional wisdom seems to be that it's prudent
to run your main engine hard for a while every day. Doing that will also go
a long way toward insuring that the engine doesn't suffer from being
"babied" too much. Without actually doing the math it would seem that
running at s/l 0.8 for 23.5hours and at s/l 1.2 for half an hour should only
cost 20 to 50 gallons over a two plus week passage (We were talking about
vessels around 40ft). That sort of schedule would have the side benefit of
giving you a daily "early warning window" into things like clogging fuel
filters or decreased raw water flow.
Economically yours,
Alex
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