Keep the propeller fixed or let it turn?
 

My brother in law, and I have had a discussion of whether it
is best - from a pure speed point of view (no consideration
to the mechanics/oil/maintenance/gearbox etc. here ...)
whether you should let your "fixed three bladed propeller"
run/turn or keep it fixed (like put into gear) when sailing
just for the wind with your sails in a 34 feet cruiser
weighing roughly 5 T ... We have - unsuccesfully - tried to
find out using the log ... the results were not conclusive -
or one of us would not admit, that the other was right ... I
think we need a testimony from someone, that has a
'scientific based valid answer' ... or just knows for sure
....

The assumption is: There is no way to move, turn, 'collapse'
anything on the propeller - the 'blades' are fixed ... (hard
to explain in a language, that is not your own ... hope you
get my point).

Anybody in this group that can convince one of us, that he
is not right? ...

--
Flemming Torp

"Flemming Torp" fletopkanelbolle2rp.danmark wrote in message
. ..
My brother in law, and I have had a discussion of whether it
is best - from a pure speed point of view (no consideration
to the mechanics/oil/maintenance/gearbox etc. here ...)
whether you should let your "fixed three bladed propeller"
run/turn or keep it fixed (like put into gear) when sailing

I always put the transmission in reverse when sailing. I don't
think that my Yanmar book says anything, but when I sailed on a
friend's Cape Dory, he said to always do so due the gearbox
that he had.

Leanne

It has been repeatedly demonstrated that airplanes glide significantly
farther (up to 20%) when the nose is raised to slow them down enough
to stop the prop and best glide speed is then resumed. I can't see
any reason why this wouldn't be true of boat propellers as well. It
also agrees with just about every other reference I've seen on the
subject.

--

Roger Long



"Flemming Torp" fletopkanelbolle2rp.danmark wrote in message
. ..
My brother in law, and I have had a discussion of whether it is
best - from a pure speed point of view (no consideration to the
mechanics/oil/maintenance/gearbox etc. here ...) whether you should
let your "fixed three bladed propeller" run/turn or keep it fixed
(like put into gear) when sailing just for the wind with your sails
in a 34 feet cruiser weighing roughly 5 T ... We have -
unsuccesfully - tried to find out using the log ... the results were
not conclusive - or one of us would not admit, that the other was
right ... I think we need a testimony from someone, that has a
'scientific based valid answer' ... or just knows for sure ...

The assumption is: There is no way to move, turn, 'collapse'
anything on the propeller - the 'blades' are fixed ... (hard to
explain in a language, that is not your own ... hope you get my
point).

Anybody in this group that can convince one of us, that he is not
right? ...

--
Flemming Torp

"Leanne" skrev i en meddelelse
...

"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
message
. ..
My brother in law, and I have had a discussion of whether
it
is best - from a pure speed point of view (no
consideration
to the mechanics/oil/maintenance/gearbox etc. here ...)
whether you should let your "fixed three bladed
propeller"
run/turn or keep it fixed (like put into gear) when
sailing

I always put the transmission in reverse when sailing. I
don't
think that my Yanmar book says anything, but when I sailed
on a
friend's Cape Dory, he said to always do so due the
gearbox
that he had.

Leanne



So do I - when cruising, but that is not my point ...
The question is: (If I race for instance): Will I increase
the speed of the boat by letting the propeller turn without
resistance? Or should I stop it from turning?

--
Flemming Torp

"Flemming Torp" fletopkanelbolle2rp.danmark wrote in message . ..

"Leanne" skrev i en meddelelse
...

"Flemming Torp" fletopkanelbolle2rp.danmark wrote in
message
. ..
My brother in law, and I have had a discussion of whether
it
is best - from a pure speed point of view (no
consideration
to the mechanics/oil/maintenance/gearbox etc. here ...)
whether you should let your "fixed three bladed
propeller"
run/turn or keep it fixed (like put into gear) when
sailing

I always put the transmission in reverse when sailing. I
don't
think that my Yanmar book says anything, but when I sailed
on a
friend's Cape Dory, he said to always do so due the
gearbox
that he had.

Leanne



So do I - when cruising, but that is not my point ...
The question is: (If I race for instance): Will I increase
the speed of the boat by letting the propeller turn without
resistance? Or should I stop it from turning?

--
Flemming Torp


It's a fact that a spinning prop creates far more drag
that a stopped prop.

CN

There is no easy way to prove this one way or the other by hand waving
for one reason: it depends on the propeller. Large ship propellers
are sometimes more efficient freewheeling, but this is not the case
for 3-blade yacht props. I suspect the the difference has to do with
the pitch, and whether or not the flow is stalled - Ship props often
high a large pitch compared to yacht props.

BTW, it worth while lining up one blade of a 3-blade with the hull
when you lock it.



Flemming Torp wrote:
My brother in law, and I have had a discussion of whether it
is best - from a pure speed point of view (no consideration
to the mechanics/oil/maintenance/gearbox etc. here ...)
whether you should let your "fixed three bladed propeller"
run/turn or keep it fixed (like put into gear) when sailing
just for the wind with your sails in a 34 feet cruiser
weighing roughly 5 T ... We have - unsuccesfully - tried to
find out using the log ... the results were not conclusive -
or one of us would not admit, that the other was right ... I
think we need a testimony from someone, that has a
'scientific based valid answer' ... or just knows for sure
...

The assumption is: There is no way to move, turn, 'collapse'
anything on the propeller - the 'blades' are fixed ... (hard
to explain in a language, that is not your own ... hope you
get my point).

Anybody in this group that can convince one of us, that he
is not right? ...

"Gary L. Burnore" wrote in message ...
On Sun, 05 Jun 2005 21:59:29 GMT, "Roger Long"
top posted like a ****ing moron and wrote:

It has been repeatedly demonstrated that airplanes glide significantly
farther (up to 20%) when the nose is raised to slow them down enough
to stop the prop and best glide speed is then resumed. I can't see
any reason why this wouldn't be true of boat propellers as well.

Because aircraft are entirely in the air an boats are partially in
water. Airplane props are feathered, boat props aren't.


I used to fly an ultralight aircraft - a Rotec Rally 2B. It had a
two-bladed wood prop that was driven by a Kohler air-cooled
432cc two-stroke engine via a centrifugal clutch and belt.

I could climb to about two or three thousand feet and shut off
the motor and the propeller would free-wheel because of the
centrifugal clutch being disengage. The glide ratio was terrible
with the prop free wheeling - one could feel the drag it caused.

I put a brake on the clutch hub and stopped the prop from
free-wheeling and the glide ration increased dramatically.

The same extra drag is evident on a boat propeller that free-wheels.
It's as if the two blades turn into a fixed disk.

CN

Pardon Sir, You can't feather a prop on a Cessna 152/172, Piper 140,
Piper Warrior, etc. But the engine out procedure is to stop the prop
for max glide distance due to less drag as the previous post explained.
Air is a fluid like water, just lighter.

Lee

Gary L. Burnore wrote:
On Sun, 05 Jun 2005 21:59:29 GMT, "Roger Long"
top posted like a ****ing moron and wrote:

It has been repeatedly demonstrated that airplanes glide significantly
farther (up to 20%) when the nose is raised to slow them down enough
to stop the prop and best glide speed is then resumed. I can't see
any reason why this wouldn't be true of boat propellers as well.

Because aircraft are entirely in the air an boats are partially in
water. Airplane props are feathered, boat props aren't.



--
gburnore@databasix dot com
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"Capt. Neal®" wrote in message
...

"Gary L. Burnore" wrote in message
...
On Sun, 05 Jun 2005 21:59:29 GMT, "Roger Long"
top posted like a ****ing moron and wrote:

It has been repeatedly demonstrated that airplanes glide significantly
farther (up to 20%) when the nose is raised to slow them down enough to
stop the prop and best glide speed is then resumed. I can't see any
reason why this wouldn't be true of boat propellers as well.

Because aircraft are entirely in the air an boats are partially in
water. Airplane props are feathered, boat props aren't.


I used to fly an ultralight aircraft - a Rotec Rally 2B. It had a
two-bladed wood prop that was driven by a Kohler air-cooled
432cc two-stroke engine via a centrifugal clutch and belt.

I could climb to about two or three thousand feet and shut off
the motor and the propeller would free-wheel because of the centrifugal
clutch being disengage. The glide ratio was terrible
with the prop free wheeling - one could feel the drag it caused.

I put a brake on the clutch hub and stopped the prop from
free-wheeling and the glide ration increased dramatically.

The same extra drag is evident on a boat propeller that free-wheels.
It's as if the two blades turn into a fixed disk.

CN

You guys need to get a room.

John Cairns

"John Cairns" wrote in message .. .

"Capt. Neal®" wrote in message ...

"Gary L. Burnore" wrote in message ...
On Sun, 05 Jun 2005 21:59:29 GMT, "Roger Long"
top posted like a ****ing moron and wrote:

It has been repeatedly demonstrated that airplanes glide significantly farther (up to 20%) when the nose is raised to slow them
down enough to stop the prop and best glide speed is then resumed. I can't see any reason why this wouldn't be true of boat
propellers as well.

Because aircraft are entirely in the air an boats are partially in
water. Airplane props are feathered, boat props aren't.


I used to fly an ultralight aircraft - a Rotec Rally 2B. It had a two-bladed wood prop that was driven by a Kohler air-cooled
432cc two-stroke engine via a centrifugal clutch and belt.

I could climb to about two or three thousand feet and shut off
the motor and the propeller would free-wheel because of the centrifugal clutch being disengage. The glide ratio was terrible
with the prop free wheeling - one could feel the drag it caused.

I put a brake on the clutch hub and stopped the prop from
free-wheeling and the glide ration increased dramatically.

The same extra drag is evident on a boat propeller that free-wheels.
It's as if the two blades turn into a fixed disk.

CN

You guys need to get a room.

John Cairns


Did you go skiing again this winter? Did your break your leg again?
I'm telling you, KKKaty, ya gotta watch that osteoporosis since you're
post-menopausal.

CN