If there truly was less drag on a locked prop than a freewheeling one
you would not have to put it in gear to lock it, a prop out of gear
would not even freewheel it there was more drag.

In article , says...


"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
:

My intuition tells me that when you ' loosen the grip' on
the propeller shaft and let the propeller turn freely, it
reduces the drag on the boat. Right or wrong?



It'd be real easy to test.

(Snip)

Nobody is interested in settling the matter. Argument is so much more fun. And
in this case, it is also trivial.

In article , says...


Mike G wrote:
In article ,
says...

On Mon, 06 Jun 2005 08:01:55 -0400, Gogarty said:


A freewheeling propeller creates more drag than a locked on.. Just
consider a helicopter. Engine out and rotors freewheeling, the aircraft
will go down safely. Rotors locked and it drops like a stone.

Bad analogy. In a helicopter when the rotors are freewheeling after the
engine dies they're still rotating in a direction that generates lift.




I just have to ask. In what way is it a bad analogy?

Perhaps you should consider an autogyro:
http://www.centennialofflight.gov/es...togyro/DI8.htm


Jeez! Are you that old? I have actually seen them.

On Mon, 6 Jun 2005 22:17:44 +0200, "Flemming Torp"
fletopkanelbolle2rp.danmark wrote:


My intuition tells me, however, that if you 'let the
propeller go', the total resistance/drag will be less and if
you start braking the turning propeller, the resistance/drag
gets bigger...

Fluid dynamics is tough on the intuition.

But if you cannot decide between two different opinions,
you *could* do what fluid dynamicists do when uncertain:
run a test.

One way:

find a spinning lure and tow it on a swivel so it can turn, behind a
boat at moderate speed (you could even do this in the bath, maybe?)
and check the drag with an ounce spring scale.

Then fix the spinner, and rerun the test.
Is the drag greater or less?

You will be surprized I expect.

[Usual disclaimer: fluid dynamics people and naval engineers know
there are scale effects as between boat sized props and little fish
size spinners.

Still, in comparing results at constant speed and constant spinner
size, you *can* get useful results.... ]

Brian Whatcott Altus, OK.

here's more various discussion from nother forum.

it's more geared to mounting alternators, but gives insight to prop
drag.

http://www.ybw.com/forums/showflat.p...e=18& fpart=1

The dinghy outboard thought experiment is not valid because the whole
system is coming to a stop and the prop is slowing as the boat is
slowing. Do it while towing the dinghy behind the big boat at a steady
speed with a scale on the tow rope and you may get a different result.

Under some circumstances, a freewheeling prop may have less drag than
a fixed one. Props on normal transmissions are not freewheeling
however. There is enough drag in the shaftline, bearings, and
transmission to upset things. Outboards, with their clutches right in
the lower unit are closer to freewheeling.

--

Roger Long

JR Gilbreath wrote:
If there truly was less drag on a locked prop than a freewheeling one
you would not have to put it in gear to lock it, a prop out of gear
would not even freewheel it there was more drag.

Why?

Gogarty wrote:

In article ,
says...

My answer would be the same as yours and also that if you have a two
blade prop, it should be locked in line with the keel if it is
possible to determine where that is etc.

Well, next time you haul you mark the shaft inside the boat to indicate
when the prop is up and down behid the keel or skeg or whatever. After
twenty years, I might yet get around to doing that.

In our case, the freewheeling prop made so much noise that one of the
first things we did was get a feathering prop. We do have evidence
that feathering the prop increases our sailing speed, in addition to
being quieter.

Ours doesn't freewheel in reverse.

So you don't really need it then.

And the cost of a feathering prop really
put me off.

The feathering prop also gave us increased speed. That alone made it
worth the money. A folding prop and a feathering prop are different
and we have the less expensive one. Plus, we found when we took the
prop off that we had a scored shaft which had to be replaced.


grandma Rosalie

In article ,
says...


If there truly was less drag on a locked prop than a freewheeling one
you would not have to put it in gear to lock it, a prop out of gear
would not even freewheel it there was more drag.

I think you have it backwards.

"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
:

I'm sory, but I can only see one picture in
alt.binaries.pictures.sports.ocean ... Am I missing
something?



Me, too. It's the one with the whole Perkins engine in it. The server
must have lost the one with just the shaft alternator behind it. I'll do
it again.

It should take it a while to propagate to your servers.