"Charles Momsen" wrote in message
...

"Wilbur Hubbard" wrote in message
anews.com...

"Charles Momsen" wrote in message
...

"Joe" wrote in message
...
On Dec 11, 12:00 pm, "Wilbur Hubbard"
wrote:
"Charles Momsen" wrote in message

...

This graph:

http://www.windows.ucar.edu/tour/lin....html&edu=high

Shows the density of water as a function of depth. Water density
changes
from 1.025 gm/cm^3 to 1.026 gm/cm^3 in 250 feet. That's a change of
0.1%
in 250 ft. Since that portion of the curve is linear, one can
estimate
that water density would change .0004% over the diameter (tip to tip)
of
a 12 inch propeller. So is a .0004% change in water density (in the
vertical plane no less) going to walk a boat sideways? Don't think
so.

Think, Momsen, think! There are very large forces at work when a
propeller
is turning at speed. You are stuck on static in your thinking. Picture
it
this way. Let's say you were riding a bicycle at 1mph and you had a ten
mile
per hour headwind. You would experience an 11mph head wind. Now, if you
aren't a girly-man you should be able to sprint up to 35mph. You would
then
experience a 45mph headwind. Suddenly your inconsequential wind has
great
consequence.

It's the same way with a propeller and the lift vs.drag coefficient.
Even a
very small density difference results in a significant drag difference
between the top half of the prop and the bottom half of the prop. But
there
is another thing that has a greater effect than density causing density
to
be only part of the equation. Water density does not vary greatly due
to the
fact that it doesn't compress easily. What does change significantly
with
depth is water pressure (divers say 1 atmosphere for every 15 feet?)
The
more pressure = the more drag for the propeller. I hope this helps.

Wilbur Hubbard

Let me use examples you may understand Neal.

Ever mix paint in a 5 gallon bucket with a paint mixing propellor on a
drill?
Why is the propellor in the paint pulled off center?

A dairy has huge tanks to store milk. They keep the creme mixed in
the milk with propellors on long shafts.
They hang straight down , he shaft is vertical. When you turn them on
the long shafts bend some in the direction of wheel walk.
Are you saying that it is pressure difference when the prop is
horizional causing the walk?

When a propellor flys off an airplane they never go straight, they
spin off in the direction of walk.

Think path of least resistance to the face of the fluke

Hope this helps.

Joe

************************************************** ************************************

************************************************** ************************************


Joe,

Thanks to your input, that of Wilbur and others I believe I have come up
with the most plausible explanation for propeller walk. This explanation
may even impress Blondie!

The cause of the prop walk is due to 2 effects, namely the Magnus Effect
and the Coanda Effect. They can be found he

http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm

The spinning prop creates a vortex of water that is moving relative to
water surrounding it, especially if the prop is angled down relative to
the water's surface.

Already a false assumption. The vortex, like that from a tip of an
airplane wing will angle upwards. Why? because water pressure lessens
towards the surface.


A right hand prop on a forward moving boat would create a downward
angling vortex that had higher relative velocity to the surrounding
moving water on the starboard side and lower on the port. Viewing the
vortex as a rotating cylinder moving through a fluid, the lift would be
generated to port, as is observed. The Coanda Effect would explain the
draggging and leakage of water laterally by the prop. I believe these
explanations are the simplest and consistent with all observed effects,
including paint stirrers in Joe's buckets.

I searched and could find no explanation of prop walk using the Magnus
or Coanda Effect. Mostly what I found was the same false pablam of water
density and other voodoo science mindlessly regurgitated by babbling
non-thinking parrots.

I resent these remarks. As I have shown density and pressure have
everything to do with prop walk.


It was only with the great minds combined here on ASA that such previous
unexplained hydrodynamic effects have come to full understanding for the
greater benefit of mankind. Yes, ASA is slowly rising from the dismal
swamp it had once become to shining paragon of truth, justice and the
American way! Good work to all, and let's keep our noses to the
grindstone!

Admiral Momsen

It will only rise from the abyss when Pansy Ganzy throws in the towel.

Wilbur Hubbard


Have you not noticed that when the dialogue is more sailing related, less
political, involves rationality, knowledge and gives less opportunity for
personal attacks his participation noticeably wanes? It's a sad, but true
observation. Hopefully he can find it within himself to deal with others
as equals, rather than from a drippy point of condensation. His mention of
prop wash was invaluable in the search for the truth about prop walk.


Rarely do I bother reading his posts lately. They lack substance more and
more as time passes. I think Dave finally managed to show him the error of
his ways. What a beating that was!

Wilbur Hubbard

"Marty" wrote in message
...
Charles Momsen wrote:
"Joe" wrote in message
...
On Dec 11, 12:00 pm, "Wilbur Hubbard"
wrote:
"Charles Momsen" wrote in message

...

This graph:
http://www.windows.ucar.edu/tour/lin....html&edu=high
Shows the density of water as a function of depth. Water density
changes
from 1.025 gm/cm^3 to 1.026 gm/cm^3 in 250 feet. That's a change of
0.1%
in 250 ft. Since that portion of the curve is linear, one can estimate
that water density would change .0004% over the diameter (tip to tip)
of
a 12 inch propeller. So is a .0004% change in water density (in the
vertical plane no less) going to walk a boat sideways? Don't think so.
Think, Momsen, think! There are very large forces at work when a
propeller
is turning at speed. You are stuck on static in your thinking. Picture
it
this way. Let's say you were riding a bicycle at 1mph and you had a ten
mile
per hour headwind. You would experience an 11mph head wind. Now, if you
aren't a girly-man you should be able to sprint up to 35mph. You would
then
experience a 45mph headwind. Suddenly your inconsequential wind has
great
consequence.

It's the same way with a propeller and the lift vs.drag coefficient.
Even a
very small density difference results in a significant drag difference
between the top half of the prop and the bottom half of the prop. But
there
is another thing that has a greater effect than density causing density
to
be only part of the equation. Water density does not vary greatly due to
the
fact that it doesn't compress easily. What does change significantly
with
depth is water pressure (divers say 1 atmosphere for every 15 feet?) The
more pressure = the more drag for the propeller. I hope this helps.

Wilbur Hubbard

Let me use examples you may understand Neal.

Ever mix paint in a 5 gallon bucket with a paint mixing propellor on a
drill?
Why is the propellor in the paint pulled off center?

A dairy has huge tanks to store milk. They keep the creme mixed in
the milk with propellors on long shafts.
They hang straight down , he shaft is vertical. When you turn them on
the long shafts bend some in the direction of wheel walk.
Are you saying that it is pressure difference when the prop is
horizional causing the walk?

When a propellor flys off an airplane they never go straight, they
spin off in the direction of walk.

Think path of least resistance to the face of the fluke

Hope this helps.

Joe

************************************************** ************************************

************************************************** ************************************


Joe,

Thanks to your input, that of Wilbur and others I believe I have come up
with the most plausible explanation for propeller walk. This explanation
may even impress Blondie!

The cause of the prop walk is due to 2 effects, namely the Magnus Effect
and the Coanda Effect. They can be found he

http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm

The spinning prop creates a vortex of water that is moving relative to
water surrounding it, especially if the prop is angled down relative to
the water's surface. A right hand prop on a forward moving boat would
create a downward angling vortex that had higher relative velocity to the
surrounding moving water on the starboard side and lower on the port.
Viewing the vortex as a rotating cylinder moving through a fluid, the
lift would be generated to port, as is observed. The Coanda Effect would
explain the draggging and leakage of water laterally by the prop. I
believe these explanations are the simplest and consistent with all
observed effects, including paint stirrers in Joe's buckets.

I searched and could find no explanation of prop walk using the Magnus or
Coanda Effect. Mostly what I found was the same false pablam of water
density and other voodoo science mindlessly regurgitated by babbling
non-thinking parrots.

Read Chapman, he explains it in exactly the same terms, (vortexes) but
leaves out calling it either Magnus or Coanda. It's a nice simple
explanation with a little drawing explaining why the port side blade on a
right hand prop has a lower angle of attack than the right side. If you
imagine perhaps the worst case: A prop has a pitch angle of 10 degrees (I
know this doesn't happen with a real prop), it's on a shaft inclined by 10
degrees. In this case the port side blade vertical at it ascends or
descends and generates no thrust, forward or aft. All the thrust comes
from the starboard side blade angled at 20 degrees, you can clearly see
there is an unbalance here. Now put it reverse and the prop throws a
rising vortex of water at the starboard side of the hull, kicking it to
port, while at the same time pulling the prop shaft sternwards from the
starboard side only, tending to skew the boat to port. Put both together
and you've got port prop walk.

Cheers
Martin

Wrong! Pitch angle doesn't matter. My outboard motor on the back of my
bluewater yacht can be put in reverse on a calm day at about 1/8 throttle
while I'm tied to my mooring. My yacht will turn slow circles caused by
prop walk. The propeller is totally horizontal.

Wilbur Hubbard

Wilbur Hubbard wrote:
"Marty" wrote in message
...
Charles Momsen wrote:
"Joe" wrote in message
...
On Dec 11, 12:00 pm, "Wilbur Hubbard"
wrote:
"Charles Momsen" wrote in message

...

This graph:
http://www.windows.ucar.edu/tour/lin....html&edu=high
Shows the density of water as a function of depth. Water density
changes
from 1.025 gm/cm^3 to 1.026 gm/cm^3 in 250 feet. That's a change of
0.1%
in 250 ft. Since that portion of the curve is linear, one can estimate
that water density would change .0004% over the diameter (tip to tip)
of
a 12 inch propeller. So is a .0004% change in water density (in the
vertical plane no less) going to walk a boat sideways? Don't think so.
Think, Momsen, think! There are very large forces at work when a
propeller
is turning at speed. You are stuck on static in your thinking. Picture
it
this way. Let's say you were riding a bicycle at 1mph and you had a ten
mile
per hour headwind. You would experience an 11mph head wind. Now, if you
aren't a girly-man you should be able to sprint up to 35mph. You would
then
experience a 45mph headwind. Suddenly your inconsequential wind has
great
consequence.

It's the same way with a propeller and the lift vs.drag coefficient.
Even a
very small density difference results in a significant drag difference
between the top half of the prop and the bottom half of the prop. But
there
is another thing that has a greater effect than density causing density
to
be only part of the equation. Water density does not vary greatly due to
the
fact that it doesn't compress easily. What does change significantly
with
depth is water pressure (divers say 1 atmosphere for every 15 feet?) The
more pressure = the more drag for the propeller. I hope this helps.

Wilbur Hubbard
Let me use examples you may understand Neal.

Ever mix paint in a 5 gallon bucket with a paint mixing propellor on a
drill?
Why is the propellor in the paint pulled off center?

A dairy has huge tanks to store milk. They keep the creme mixed in
the milk with propellors on long shafts.
They hang straight down , he shaft is vertical. When you turn them on
the long shafts bend some in the direction of wheel walk.
Are you saying that it is pressure difference when the prop is
horizional causing the walk?

When a propellor flys off an airplane they never go straight, they
spin off in the direction of walk.

Think path of least resistance to the face of the fluke

Hope this helps.

Joe

************************************************** ************************************

************************************************** ************************************


Joe,

Thanks to your input, that of Wilbur and others I believe I have come up
with the most plausible explanation for propeller walk. This explanation
may even impress Blondie!

The cause of the prop walk is due to 2 effects, namely the Magnus Effect
and the Coanda Effect. They can be found he

http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm

The spinning prop creates a vortex of water that is moving relative to
water surrounding it, especially if the prop is angled down relative to
the water's surface. A right hand prop on a forward moving boat would
create a downward angling vortex that had higher relative velocity to the
surrounding moving water on the starboard side and lower on the port.
Viewing the vortex as a rotating cylinder moving through a fluid, the
lift would be generated to port, as is observed. The Coanda Effect would
explain the draggging and leakage of water laterally by the prop. I
believe these explanations are the simplest and consistent with all
observed effects, including paint stirrers in Joe's buckets.

I searched and could find no explanation of prop walk using the Magnus or
Coanda Effect. Mostly what I found was the same false pablam of water
density and other voodoo science mindlessly regurgitated by babbling
non-thinking parrots.
Read Chapman, he explains it in exactly the same terms, (vortexes) but
leaves out calling it either Magnus or Coanda. It's a nice simple
explanation with a little drawing explaining why the port side blade on a
right hand prop has a lower angle of attack than the right side. If you
imagine perhaps the worst case: A prop has a pitch angle of 10 degrees (I
know this doesn't happen with a real prop), it's on a shaft inclined by 10
degrees. In this case the port side blade vertical at it ascends or
descends and generates no thrust, forward or aft. All the thrust comes
from the starboard side blade angled at 20 degrees, you can clearly see
there is an unbalance here. Now put it reverse and the prop throws a
rising vortex of water at the starboard side of the hull, kicking it to
port, while at the same time pulling the prop shaft sternwards from the
starboard side only, tending to skew the boat to port. Put both together
and you've got port prop walk.

Cheers
Martin

Wrong! Pitch angle doesn't matter. My outboard motor on the back of my
bluewater yacht can be put in reverse on a calm day at about 1/8 throttle
while I'm tied to my mooring. My yacht will turn slow circles caused by
prop walk. The propeller is totally horizontal.


Wrong yourself. Pitch angle contributes. In your case, the vortex is
propelled upward on the starboard side, impinging the starboard side of
your boat, on the port side the vortex tends be more downward. Pitch
angle just adds to the effect.

Cheers
Martin

Charles Momsen wrote:
"Marty" wrote in message
...
Charles Momsen wrote:
"Joe" wrote in message
...
On Dec 11, 12:00 pm, "Wilbur Hubbard"
wrote:
"Charles Momsen" wrote in message

...

This graph:
http://www.windows.ucar.edu/tour/lin....html&edu=high
Shows the density of water as a function of depth. Water density
changes
from 1.025 gm/cm^3 to 1.026 gm/cm^3 in 250 feet. That's a change of
0.1%
in 250 ft. Since that portion of the curve is linear, one can estimate
that water density would change .0004% over the diameter (tip to tip)
of
a 12 inch propeller. So is a .0004% change in water density (in the
vertical plane no less) going to walk a boat sideways? Don't think so.
Think, Momsen, think! There are very large forces at work when a
propeller
is turning at speed. You are stuck on static in your thinking. Picture
it
this way. Let's say you were riding a bicycle at 1mph and you had a ten
mile
per hour headwind. You would experience an 11mph head wind. Now, if you
aren't a girly-man you should be able to sprint up to 35mph. You would
then
experience a 45mph headwind. Suddenly your inconsequential wind has
great
consequence.

It's the same way with a propeller and the lift vs.drag coefficient.
Even a
very small density difference results in a significant drag difference
between the top half of the prop and the bottom half of the prop. But
there
is another thing that has a greater effect than density causing density
to
be only part of the equation. Water density does not vary greatly due to
the
fact that it doesn't compress easily. What does change significantly
with
depth is water pressure (divers say 1 atmosphere for every 15 feet?) The
more pressure = the more drag for the propeller. I hope this helps.

Wilbur Hubbard
Let me use examples you may understand Neal.

Ever mix paint in a 5 gallon bucket with a paint mixing propellor on a
drill?
Why is the propellor in the paint pulled off center?

A dairy has huge tanks to store milk. They keep the creme mixed in
the milk with propellors on long shafts.
They hang straight down , he shaft is vertical. When you turn them on
the long shafts bend some in the direction of wheel walk.
Are you saying that it is pressure difference when the prop is
horizional causing the walk?

When a propellor flys off an airplane they never go straight, they
spin off in the direction of walk.

Think path of least resistance to the face of the fluke

Hope this helps.

Joe

************************************************** ************************************

************************************************** ************************************


Joe,

Thanks to your input, that of Wilbur and others I believe I have come up
with the most plausible explanation for propeller walk. This explanation
may even impress Blondie!

The cause of the prop walk is due to 2 effects, namely the Magnus Effect
and the Coanda Effect. They can be found he

http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm

The spinning prop creates a vortex of water that is moving relative to
water surrounding it, especially if the prop is angled down relative to
the water's surface. A right hand prop on a forward moving boat would
create a downward angling vortex that had higher relative velocity to the
surrounding moving water on the starboard side and lower on the port.
Viewing the vortex as a rotating cylinder moving through a fluid, the
lift would be generated to port, as is observed. The Coanda Effect would
explain the draggging and leakage of water laterally by the prop. I
believe these explanations are the simplest and consistent with all
observed effects, including paint stirrers in Joe's buckets.

I searched and could find no explanation of prop walk using the Magnus or
Coanda Effect. Mostly what I found was the same false pablam of water
density and other voodoo science mindlessly regurgitated by babbling
non-thinking parrots.
Read Chapman, he explains it in exactly the same terms, (vortexes) but
leaves out calling it either Magnus or Coanda. It's a nice simple
explanation with a little drawing explaining why the port side blade on a
right hand prop has a lower angle of attack than the right side. If you
imagine perhaps the worst case: A prop has a pitch angle of 10 degrees (I
know this doesn't happen with a real prop), it's on a shaft inclined by 10
degrees. In this case the port side blade vertical at it ascends or
descends and generates no thrust, forward or aft. All the thrust comes
from the starboard side blade angled at 20 degrees, you can clearly see
there is an unbalance here. Now put it reverse and the prop throws a
rising vortex of water at the starboard side of the hull, kicking it to
port, while at the same time pulling the prop shaft sternwards from the
starboard side only, tending to skew the boat to port. Put both together
and you've got port prop walk.

Cheers
Martin

If it's the explanation I'm thinking of it involves the total path length
traveled by the blade tip on either ascent or descent (with the boat moving
forward). I could see the argument there but could not resolve if a longer
path resulted in less thrust force or more and the same with the short path
length. This same argument applies to retreating blade stall in helicopters.
I'll look through Chapman and see what he says.

The angle of attack argument only holds if the velocity of water is
significant compared to the tangential velocity of the blade. If the water
velocity is zero then the angle of attack is the same regardless of
orientation. If the blade is turning 500 rpm and is 12 inch diameter the tip
is moving at 314 inches/sec or 214 mph.




214 mph?

500rpm * (pi *12)in/rev = 1.885E4 inches/min

1.885E4 in/min * 60 min/hr = 1.131E6 inches/hour

1.131E4 in/hr / 63360 in/mi = 17.85 mile/hr

18 mph is a tad bit slower than 214.....

Back to remedial slide-rule class for you!

Cheers
Martin

"Marty" wrote in message
...
Wilbur Hubbard wrote:
"Marty" wrote in message
...
Charles Momsen wrote:
"Joe" wrote in message
...
On Dec 11, 12:00 pm, "Wilbur Hubbard"
wrote:
"Charles Momsen" wrote in message

...

This graph:
http://www.windows.ucar.edu/tour/lin....html&edu=high
Shows the density of water as a function of depth. Water density
changes
from 1.025 gm/cm^3 to 1.026 gm/cm^3 in 250 feet. That's a change of
0.1%
in 250 ft. Since that portion of the curve is linear, one can
estimate
that water density would change .0004% over the diameter (tip to tip)
of
a 12 inch propeller. So is a .0004% change in water density (in the
vertical plane no less) going to walk a boat sideways? Don't think
so.
Think, Momsen, think! There are very large forces at work when a
propeller
is turning at speed. You are stuck on static in your thinking. Picture
it
this way. Let's say you were riding a bicycle at 1mph and you had a
ten mile
per hour headwind. You would experience an 11mph head wind. Now, if
you
aren't a girly-man you should be able to sprint up to 35mph. You would
then
experience a 45mph headwind. Suddenly your inconsequential wind has
great
consequence.

It's the same way with a propeller and the lift vs.drag coefficient.
Even a
very small density difference results in a significant drag difference
between the top half of the prop and the bottom half of the prop. But
there
is another thing that has a greater effect than density causing
density to
be only part of the equation. Water density does not vary greatly due
to the
fact that it doesn't compress easily. What does change significantly
with
depth is water pressure (divers say 1 atmosphere for every 15 feet?)
The
more pressure = the more drag for the propeller. I hope this helps.

Wilbur Hubbard
Let me use examples you may understand Neal.

Ever mix paint in a 5 gallon bucket with a paint mixing propellor on a
drill?
Why is the propellor in the paint pulled off center?

A dairy has huge tanks to store milk. They keep the creme mixed in
the milk with propellors on long shafts.
They hang straight down , he shaft is vertical. When you turn them on
the long shafts bend some in the direction of wheel walk.
Are you saying that it is pressure difference when the prop is
horizional causing the walk?

When a propellor flys off an airplane they never go straight, they
spin off in the direction of walk.

Think path of least resistance to the face of the fluke

Hope this helps.

Joe

************************************************** ************************************

************************************************** ************************************


Joe,

Thanks to your input, that of Wilbur and others I believe I have come
up with the most plausible explanation for propeller walk. This
explanation may even impress Blondie!

The cause of the prop walk is due to 2 effects, namely the Magnus
Effect and the Coanda Effect. They can be found he

http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm

The spinning prop creates a vortex of water that is moving relative to
water surrounding it, especially if the prop is angled down relative to
the water's surface. A right hand prop on a forward moving boat would
create a downward angling vortex that had higher relative velocity to
the surrounding moving water on the starboard side and lower on the
port. Viewing the vortex as a rotating cylinder moving through a fluid,
the lift would be generated to port, as is observed. The Coanda Effect
would explain the draggging and leakage of water laterally by the prop.
I believe these explanations are the simplest and consistent with all
observed effects, including paint stirrers in Joe's buckets.

I searched and could find no explanation of prop walk using the Magnus
or Coanda Effect. Mostly what I found was the same false pablam of
water density and other voodoo science mindlessly regurgitated by
babbling non-thinking parrots.
Read Chapman, he explains it in exactly the same terms, (vortexes) but
leaves out calling it either Magnus or Coanda. It's a nice simple
explanation with a little drawing explaining why the port side blade on
a right hand prop has a lower angle of attack than the right side. If
you imagine perhaps the worst case: A prop has a pitch angle of 10
degrees (I know this doesn't happen with a real prop), it's on a shaft
inclined by 10 degrees. In this case the port side blade vertical at it
ascends or descends and generates no thrust, forward or aft. All the
thrust comes from the starboard side blade angled at 20 degrees, you can
clearly see there is an unbalance here. Now put it reverse and the prop
throws a rising vortex of water at the starboard side of the hull,
kicking it to port, while at the same time pulling the prop shaft
sternwards from the starboard side only, tending to skew the boat to
port. Put both together and you've got port prop walk.

Cheers
Martin

Wrong! Pitch angle doesn't matter. My outboard motor on the back of my
bluewater yacht can be put in reverse on a calm day at about 1/8 throttle
while I'm tied to my mooring. My yacht will turn slow circles caused by
prop walk. The propeller is totally horizontal.


Wrong yourself. Pitch angle contributes. In your case, the vortex is
propelled upward on the starboard side, impinging the starboard side of
your boat, on the port side the vortex tends be more downward. Pitch
angle just adds to the effect.

Cheers
Martin

So you're talking about pitch of the prop as inches per revolution and not
pitch as angle of the prop shaft?
That's going off on a tangent as those talking about pitch angle in this
thread are talking about the angle of the prop shaft from the horizontal or
at least that's the impression I got.

Wilbur Hubbard

Wilbur Hubbard wrote:
"Marty" wrote in message
...
Wilbur Hubbard wrote:
"Marty" wrote in message
...
Charles Momsen wrote:
"Joe" wrote in message
...
On Dec 11, 12:00 pm, "Wilbur Hubbard"
wrote:
"Charles Momsen" wrote in message

...

This graph:
http://www.windows.ucar.edu/tour/lin....html&edu=high
Shows the density of water as a function of depth. Water density
changes
from 1.025 gm/cm^3 to 1.026 gm/cm^3 in 250 feet. That's a change of
0.1%
in 250 ft. Since that portion of the curve is linear, one can
estimate
that water density would change .0004% over the diameter (tip to tip)
of
a 12 inch propeller. So is a .0004% change in water density (in the
vertical plane no less) going to walk a boat sideways? Don't think
so.
Think, Momsen, think! There are very large forces at work when a
propeller
is turning at speed. You are stuck on static in your thinking. Picture
it
this way. Let's say you were riding a bicycle at 1mph and you had a
ten mile
per hour headwind. You would experience an 11mph head wind. Now, if
you
aren't a girly-man you should be able to sprint up to 35mph. You would
then
experience a 45mph headwind. Suddenly your inconsequential wind has
great
consequence.

It's the same way with a propeller and the lift vs.drag coefficient.
Even a
very small density difference results in a significant drag difference
between the top half of the prop and the bottom half of the prop. But
there
is another thing that has a greater effect than density causing
density to
be only part of the equation. Water density does not vary greatly due
to the
fact that it doesn't compress easily. What does change significantly
with
depth is water pressure (divers say 1 atmosphere for every 15 feet?)
The
more pressure = the more drag for the propeller. I hope this helps.

Wilbur Hubbard
Let me use examples you may understand Neal.

Ever mix paint in a 5 gallon bucket with a paint mixing propellor on a
drill?
Why is the propellor in the paint pulled off center?

A dairy has huge tanks to store milk. They keep the creme mixed in
the milk with propellors on long shafts.
They hang straight down , he shaft is vertical. When you turn them on
the long shafts bend some in the direction of wheel walk.
Are you saying that it is pressure difference when the prop is
horizional causing the walk?

When a propellor flys off an airplane they never go straight, they
spin off in the direction of walk.

Think path of least resistance to the face of the fluke

Hope this helps.

Joe

************************************************** ************************************

************************************************** ************************************


Joe,

Thanks to your input, that of Wilbur and others I believe I have come
up with the most plausible explanation for propeller walk. This
explanation may even impress Blondie!

The cause of the prop walk is due to 2 effects, namely the Magnus
Effect and the Coanda Effect. They can be found he

http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm

The spinning prop creates a vortex of water that is moving relative to
water surrounding it, especially if the prop is angled down relative to
the water's surface. A right hand prop on a forward moving boat would
create a downward angling vortex that had higher relative velocity to
the surrounding moving water on the starboard side and lower on the
port. Viewing the vortex as a rotating cylinder moving through a fluid,
the lift would be generated to port, as is observed. The Coanda Effect
would explain the draggging and leakage of water laterally by the prop.
I believe these explanations are the simplest and consistent with all
observed effects, including paint stirrers in Joe's buckets.

I searched and could find no explanation of prop walk using the Magnus
or Coanda Effect. Mostly what I found was the same false pablam of
water density and other voodoo science mindlessly regurgitated by
babbling non-thinking parrots.
Read Chapman, he explains it in exactly the same terms, (vortexes) but
leaves out calling it either Magnus or Coanda. It's a nice simple
explanation with a little drawing explaining why the port side blade on
a right hand prop has a lower angle of attack than the right side. If
you imagine perhaps the worst case: A prop has a pitch angle of 10
degrees (I know this doesn't happen with a real prop), it's on a shaft
inclined by 10 degrees. In this case the port side blade vertical at it
ascends or descends and generates no thrust, forward or aft. All the
thrust comes from the starboard side blade angled at 20 degrees, you can
clearly see there is an unbalance here. Now put it reverse and the prop
throws a rising vortex of water at the starboard side of the hull,
kicking it to port, while at the same time pulling the prop shaft
sternwards from the starboard side only, tending to skew the boat to
port. Put both together and you've got port prop walk.

Cheers
Martin
Wrong! Pitch angle doesn't matter. My outboard motor on the back of my
bluewater yacht can be put in reverse on a calm day at about 1/8 throttle
while I'm tied to my mooring. My yacht will turn slow circles caused by
prop walk. The propeller is totally horizontal.

Wrong yourself. Pitch angle contributes. In your case, the vortex is
propelled upward on the starboard side, impinging the starboard side of
your boat, on the port side the vortex tends be more downward. Pitch
angle just adds to the effect.

Cheers
Martin

So you're talking about pitch of the prop as inches per revolution and not
pitch as angle of the prop shaft?
That's going off on a tangent as those talking about pitch angle in this
thread are talking about the angle of the prop shaft from the horizontal or
at least that's the impression I got.

I do hope you're not being deliberately obtuse. I specifically
mentioned the pitch of the propeller blades and the angle of the shaft
in the same post so as to make it clear.

Anyway if you like, change my 'Pitch Angle" and yours, to 'Shaft Angle',
and all is well. If the shaft is horizontal, blade pitch still causes
the vortex to rise on the starboard side, inclining the shaft just adds
to the effect

Cheers
Martin

"Wilbur Hubbard" wrote in message
anews.com...

So you're talking about pitch of the prop as inches per revolution and not
pitch as angle of the prop shaft?
That's going off on a tangent as those talking about pitch angle in this
thread are talking about the angle of the prop shaft from the horizontal
or at least that's the impression I got.

Wilbur Hubbard

You are confused then. Propeller pitch is the distance a prop would screw
itself forward in one revolution if there was no slip.
I noticed from your earlier post that your 'bluewater yacht' has an outboard
on the stern. ROFL

"Marty" wrote in message
...
Wilbur Hubbard wrote:
"Marty" wrote in message
...
Wilbur Hubbard wrote:
"Marty" wrote in message
...
Charles Momsen wrote:
"Joe" wrote in message
...
On Dec 11, 12:00 pm, "Wilbur Hubbard"
wrote:
"Charles Momsen" wrote in message

...

This graph:
http://www.windows.ucar.edu/tour/lin....html&edu=high
Shows the density of water as a function of depth. Water density
changes
from 1.025 gm/cm^3 to 1.026 gm/cm^3 in 250 feet. That's a change of
0.1%
in 250 ft. Since that portion of the curve is linear, one can
estimate
that water density would change .0004% over the diameter (tip to
tip) of
a 12 inch propeller. So is a .0004% change in water density (in the
vertical plane no less) going to walk a boat sideways? Don't think
so.
Think, Momsen, think! There are very large forces at work when a
propeller
is turning at speed. You are stuck on static in your thinking.
Picture it
this way. Let's say you were riding a bicycle at 1mph and you had a
ten mile
per hour headwind. You would experience an 11mph head wind. Now, if
you
aren't a girly-man you should be able to sprint up to 35mph. You
would then
experience a 45mph headwind. Suddenly your inconsequential wind has
great
consequence.

It's the same way with a propeller and the lift vs.drag coefficient.
Even a
very small density difference results in a significant drag
difference
between the top half of the prop and the bottom half of the prop.
But there
is another thing that has a greater effect than density causing
density to
be only part of the equation. Water density does not vary greatly
due to the
fact that it doesn't compress easily. What does change significantly
with
depth is water pressure (divers say 1 atmosphere for every 15 feet?)
The
more pressure = the more drag for the propeller. I hope this helps.

Wilbur Hubbard
Let me use examples you may understand Neal.

Ever mix paint in a 5 gallon bucket with a paint mixing propellor on
a
drill?
Why is the propellor in the paint pulled off center?

A dairy has huge tanks to store milk. They keep the creme mixed in
the milk with propellors on long shafts.
They hang straight down , he shaft is vertical. When you turn them on
the long shafts bend some in the direction of wheel walk.
Are you saying that it is pressure difference when the prop is
horizional causing the walk?

When a propellor flys off an airplane they never go straight, they
spin off in the direction of walk.

Think path of least resistance to the face of the fluke

Hope this helps.

Joe

************************************************** ************************************

************************************************** ************************************


Joe,

Thanks to your input, that of Wilbur and others I believe I have come
up with the most plausible explanation for propeller walk. This
explanation may even impress Blondie!

The cause of the prop walk is due to 2 effects, namely the Magnus
Effect and the Coanda Effect. They can be found he

http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm

The spinning prop creates a vortex of water that is moving relative
to water surrounding it, especially if the prop is angled down
relative to the water's surface. A right hand prop on a forward
moving boat would create a downward angling vortex that had higher
relative velocity to the surrounding moving water on the starboard
side and lower on the port. Viewing the vortex as a rotating cylinder
moving through a fluid, the lift would be generated to port, as is
observed. The Coanda Effect would explain the draggging and leakage
of water laterally by the prop. I believe these explanations are the
simplest and consistent with all observed effects, including paint
stirrers in Joe's buckets.

I searched and could find no explanation of prop walk using the
Magnus or Coanda Effect. Mostly what I found was the same false
pablam of water density and other voodoo science mindlessly
regurgitated by babbling non-thinking parrots.
Read Chapman, he explains it in exactly the same terms, (vortexes) but
leaves out calling it either Magnus or Coanda. It's a nice simple
explanation with a little drawing explaining why the port side blade
on a right hand prop has a lower angle of attack than the right side.
If you imagine perhaps the worst case: A prop has a pitch angle of 10
degrees (I know this doesn't happen with a real prop), it's on a shaft
inclined by 10 degrees. In this case the port side blade vertical at
it ascends or descends and generates no thrust, forward or aft. All
the thrust comes from the starboard side blade angled at 20 degrees,
you can clearly see there is an unbalance here. Now put it reverse
and the prop throws a rising vortex of water at the starboard side of
the hull, kicking it to port, while at the same time pulling the prop
shaft sternwards from the starboard side only, tending to skew the
boat to port. Put both together and you've got port prop walk.

Cheers
Martin
Wrong! Pitch angle doesn't matter. My outboard motor on the back of my
bluewater yacht can be put in reverse on a calm day at about 1/8
throttle while I'm tied to my mooring. My yacht will turn slow circles
caused by prop walk. The propeller is totally horizontal.

Wrong yourself. Pitch angle contributes. In your case, the vortex is
propelled upward on the starboard side, impinging the starboard side of
your boat, on the port side the vortex tends be more downward. Pitch
angle just adds to the effect.

Cheers
Martin

So you're talking about pitch of the prop as inches per revolution and
not pitch as angle of the prop shaft?
That's going off on a tangent as those talking about pitch angle in this
thread are talking about the angle of the prop shaft from the horizontal
or at least that's the impression I got.

I do hope you're not being deliberately obtuse. I specifically mentioned
the pitch of the propeller blades and the angle of the shaft in the same
post so as to make it clear.

Anyway if you like, change my 'Pitch Angle" and yours, to 'Shaft Angle',
and all is well. If the shaft is horizontal, blade pitch still causes the
vortex to rise on the starboard side, inclining the shaft just adds to the
effect

Cheers
Martin

I see the logic in your thinking. So, in my previous example, what if were
to take the motor off the transom and attach it to the end of a hundred foot
long pole that was firmly affixed to the stern of the yacht and did the same
thing with the motor in reverse. I bet the boat would still turn lazy
circles even though no water stream was hitting the hull.

Wilbur Hubbard

Edgar wrote:
"Wilbur Hubbard" wrote in message
anews.com...

So you're talking about pitch of the prop as inches per revolution and not
pitch as angle of the prop shaft?
That's going off on a tangent as those talking about pitch angle in this
thread are talking about the angle of the prop shaft from the horizontal
or at least that's the impression I got.

Wilbur Hubbard

You are confused then. Propeller pitch is the distance a prop would screw
itself forward in one revolution if there was no slip.
I noticed from your earlier post that your 'bluewater yacht' has an outboard
on the stern. ROFL




I thought it odd also Edgar. Every mariner worth his salt knows that
propeller pitch refers to the distance the prop would travel through the
water under ideal conditions, usually expressed in inches per
revolution, the use of degrees is only for academic purposes as the
angle of the blade is not uniform from hub to tip in normal
applications. Shaft angle should be rather self explanatory.

Cheers
Martin

"Edgar" wrote in message
...

"Wilbur Hubbard" wrote in message
anews.com...

So you're talking about pitch of the prop as inches per revolution and
not pitch as angle of the prop shaft?
That's going off on a tangent as those talking about pitch angle in this
thread are talking about the angle of the prop shaft from the horizontal
or at least that's the impression I got.

Wilbur Hubbard

You are confused then. Propeller pitch is the distance a prop would screw
itself forward in one revolution if there was no slip.
I noticed from your earlier post that your 'bluewater yacht' has an
outboard on the stern. ROFL


Sails, my boy, sails. Ain't no motor sailer in the world that can cross the
Pacific under power. A motor needs only be used to get into or out of port
when there is no wind. The rest of the time it can be removed from the
transom and stowed safely away below.

Wilbur Hubbard