Duncan Heenan wrote:
> I usually sail with the prop locked (by putting it in reverse gear -
fixed
> 2 bladed low tech prop on a sail drive). This avoids the annoying noise
of
> the gearbox turning over and is something that a lot of sailors do.
> However, the handbook for the Volvo MD 2030, says to leave it in neutral
> when sailing, and several people have told me that I am significantly
> increasing drag by locking the prop. What do the URS gurus recommend
> (Please don't recommend a change of prop, as I want to stay on topic.)
There are 3 issues here.
One is what is best for the engine. If the manual says to let it spin,
it must do so for a reason, though it would be interesting to know what
the reason is. Do they say why?
Another is the noise. If it bothers you, lock it.
Finally there's the speed thing. Indications are that it makes so little
difference that folk aren't sure whether locked or unlocked drag is
bigger.
I expect Ian will know the answer. My intuition tells me that locked drag
is bigger, because although some power is being extracted by the prop from
the water flowing past, and expended in overcoming the odd bit of friction
here and there, and in stirring (and probably slightly heating) the
gearbox
oil, it's so little as to be negligible compared with the effect that
presumably the overall force "seen" by the water ru****ng past a fixed
blade
is bigger than with a spinning blade.
Things might be different if one were seeking to extract a serious amount
of power from the prop. One might want to decouple it from the engine,
and rig up some fancy gearing to drive a reverse windmill to help the
boat sail faster...
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