"Mike G" skrev i en meddelelse
ews.com...
In article ,
"Flemming
Torp" fletopkanelbolle2rp.danmark says...
I agree, that the practical difference might be dismissal
... but in a race every second counts per NM ... and it
is
not easy to get a fixed propeller out of the water ;-) -
and
I'm pretty curious of knowing the correct answer to my
question - preferably backed by solid science as I'm not
a
scientist ...

When cruising, I would always lock the propeller - or
follow
Larry's advice - use the energy generated ... that is
something I will consider ti implement in the future ...

--
Flemming Torp





Well, if you are racing and can't get the prop out of the
water I can
see where it may be of concern but if you're looking for a
solid science
answer I'd have to venture to say that there are so many
variables
involved only a practical application with the boat
involved would work.

Drag is drag and if you can set a straight course with a
constant speed,
difficult under sail even in ideal conditions but still do
able, just
locking and unlocking the prop and seeing what it does to
your speed
should provide the answer.

That's exactly, what we have tried, but the conditions were
not ideal, so we did not - unfortunately - come up with some
'conclusive empiric evidence' ...

However, I'd have to opine that there is a difference
between a free
wheeling prop and one that is not only spinning but
driving an
generator/alternator. There is no free ride. A prop
working a generator
requires more energy then a free wheeling one and the only
place that
energy can come from is the forward speed of the boat.

That's also what my intuition tells me, but listening to
other people in this group, I get the impression, that my
intuition is not valid in this case ...

Again, the difference may be negligible but if you are
concerned with
thousands of a second, as you would be if racing, you have
now
introduced one more variable that has to be considered.

I do not understand - a new variable? My question is simple:
.... If all other things are equal, should I stop my
propeller or should I let i turn freely?

I'm afraid you can't really get a "just speed" answer and
expect an
answer backed by science without considering conservation
of energy,
every action has an......... and so on.

I can't prove it but my money would be on a truly free
spinning prop. A
fixed prop wants to spin and is going to use energy trying
to do so.
It's going to fight forward motion harder then a free
spinning prop. A
prop with a generator on it will spin but not without the
loss of energy
required to also turn the generator, a free spinning prop
requires only
the energy required to spin it. It'll, pardon the pun, go
with the flow.
Some energy penalty but less then the first two scenario's

Again, the only place the energy required can come from is
the forward
motion of the boat.

--
Mike G.
Heirloom Woods

www.heirloom-woods.net

My problem is, that I can not see, that your above argument
is wrong ... but some other readers in this group tell me,
it is not correct ... Unfortunately, I do not
know/understand the laws of physics governing this situation
....

--
Flemming Torp