JAXAshby wrote:

the original (and incorrect) term was "P-Torque". that was replaced (to some
extent) by the term "P-Thrust" as in asymetrical thrust due to the angling of
the disc of the prop relative to forward motion. "P-Factor" is now used by
idiots and for idiot who don't have a clew what is going on.

On Jaxworld maybe ... You truly are an idiot. So how about a cite for
the use of those terms on this planet.

Oh, silly me, asking Jax to backup one of his febrile claims.

btw ricky, you must the only person on the planet who claims to have an Airline
Transport rating who doesn't know the difference between slots and slats.

Another bad drug reaction, Jax? Please show where I wrote anything that
would indicate such an absurd position on my part.

Oh, silly me, asking Jax to backup one of his febrile claims.

Take your pills, Jax and get some rest.

Rick

gene, *you* are the guy who said prop wash spirals and thus twists an airplane
one way or the other, and no one else( and thus a smaller rudder would reduce
the effect, AND a larger rudder would reduce it).

AND, prop wash on a boat must push against something or the boat won't go.

So, who is the clewless one?

no, gene. the prop pushes against the water, NOT the prop wash. and yes
you
did state that prop walk is due to the prop wash spiralling, and thus
pushing
against god knows what.

dumb, gene, as in stupid on your part.


No... stupid on my part would be continuing this thread with the
terminally clueless....




--
23' Grady White, out of Southport, NC.

http://myworkshop.idleplay.net/cavern/ Homepage
http://www.southharbourvillageinn.com/directions.asp Where Southport,NC is
located.
http://southharbourvillageinn.linksysnet.com Real Time
Pictures at My Marina
http://www.thebayguide.com/rec.boats Rec.boats at
Lee Yeaton's Bayguide

rickie, recess is over. go back to class.

the original (and incorrect) term was "P-Torque". that was replaced (to
some
extent) by the term "P-Thrust" as in asymetrical thrust due to the angling
of
the disc of the prop relative to forward motion. "P-Factor" is now used by
idiots and for idiot who don't have a clew what is going on.

On Jaxworld maybe ... You truly are an idiot. So how about a cite for
the use of those terms on this planet.

Oh, silly me, asking Jax to backup one of his febrile claims.

btw ricky, you must the only person on the planet who claims to have an
Airline
Transport rating who doesn't know the difference between slots and slats.

Another bad drug reaction, Jax? Please show where I wrote anything that
would indicate such an absurd position on my part.

Oh, silly me, asking Jax to backup one of his febrile claims.

Take your pills, Jax and get some rest.

Rick

Cornered and, as seen here a thousand times before, unable to support a
single word of his paranoid fantasies, Jax could only respond with this
brilliant retort:

rickie, recess is over. go back to class.

That is SO Jax ... come on out and play Jax, tell us all about your
taildragger time and show those cites, show us those posts ...

Bwahahahahahahahahahahahah what a poseur you are. But, sadly, and
typically Jax, not even a good poseur.

Rick

rickie, recess is over. go back to class.


Cornered and, as seen here a thousand times before, unable to support a
single word of his paranoid fantasies, Jax could only respond with this
brilliant retort:

rickie, recess is over. go back to class.

That is SO Jax ... come on out and play Jax, tell us all about your
taildragger time and show those cites, show us those posts ...

Bwahahahahahahahahahahahah what a poseur you are. But, sadly, and
typically Jax, not even a good poseur.

Rick

Subject: Angle of prop shaft - theoretical question.
From: Wayne.B
Date: 06/05/2004 21:28 Pacific Standard Time
Message-id:

On 05 Jun 2004 22:44:53 GMT, (Shen44) wrote:

the basic issue (propwalk) is caused by prop rotation and all
other factors may assist or decrease it, but the basic "phenom" occurs when
you
rotate the prop.

============================================

Of course, but what is the cause of the asymetric thrust? THAT is the
question. Everyone agrees that a prop with a horizontal shaft still
exhibits prop walk, implying that the bottom the prop is more
efficient at providing thrust than the top. Lots of theories have
been provided but none that seem totally convincing since prop walk
still exists to one degree or another on deep props, that have plenty
of hull clearance.



First off, ignore any parallel discussions of aircraft propellors. An aircraft
propellor work in one medium ... air. A boat propellor impacts two mediums ...
water and air (if you need confirmation of this, look astern of a boat
underway, under power ... you will see a wash/water, being lifted above the
surface in a rooster tail or lessor version thereof.
Now, go to a boatyard and stand in front of a propellor on some boat out of the
water.
Look at the angle/pitch of the blade, then start slowly rotating the blade
(assuming RH and you are standing in front of it) and visualize you are pushing
against water. As you rotate, (starting in the vertical up position) you will
note that the blade angle/pitch is pushing back and down against the water.
Water is not compressible. By pushing back and down, you are pushing against a
"solid" mass of water and are most efficient.
Now, as the propellor rotates it also pushes to the side against that "solid
mass of water, but as it starts rotating up, the solid mass becomes a relative
small column of water with air above it (air - highly compressible).
The propellor blade is now pushing back, but also up, and lifting that water up
and away - i.e., no longer a solid wall of water, into the air, and it becomes
less efficient.
The same applies as the blade re aproaches the vertical.
The forces of greatest efficiency are on the downward and sideward rotation of
the blade (pushing the stern to stbd when going ahead -left turn).
The same applies to backing, but because the prop is now pulling the boat, the
effect is far more noticeable.
Someone is bound to discuss the overhang of the hull, over the prop, should
negate this. Not so. That overhang is relatively short and variable, so that
although it may affect the degree, it will not stop the results.
BG And this is my theory and I'magonna stick to it......for now.

Shen

Overall, Shen and I are in agreement on this issue, as to the cause when
it relates to boats (for what that's worth), but again, my main point is
that you should normally expect to see this reaction in a specific
direction for a specific prop rotation no matter the angle of the shaft
or hull configuration or relative depth of the prop.
In fact, as someone else has said, this is much the basis of the
"surface piercing" Arnesson prop setup.
As a kind of further note, I was reading some comments from guys running
"go fast" Donzi types, discussing switching from outboard turning to
inboard turning props. This seemed to give them an increase in speed
(unrelated to this discussion) but also made the boats handle poorly
around the dock (totally understandable to me as it completely changes
the handling characteristics), but the important point was that these
were I/O's and the reason for this handling change was simple - propwalk
- and the propwalk was/is basically, caused by the propellor rotation,
as this shows - at least to me.

otn

On 07 Jun 2004 03:25:31 GMT, (Shen44) wrote:

Subject: Angle of prop shaft - theoretical question.
From: Wayne.B
Date: 06/05/2004 21:28 Pacific Standard Time
Message-id:

On 05 Jun 2004 22:44:53 GMT, (Shen44) wrote:

the basic issue (propwalk) is caused by prop rotation and all
other factors may assist or decrease it, but the basic "phenom" occurs when
you
rotate the prop.

============================================

Of course, but what is the cause of the asymetric thrust? THAT is the
question. Everyone agrees that a prop with a horizontal shaft still
exhibits prop walk, implying that the bottom the prop is more
efficient at providing thrust than the top. Lots of theories have
been provided but none that seem totally convincing since prop walk
still exists to one degree or another on deep props, that have plenty
of hull clearance.



First off, ignore any parallel discussions of aircraft propellors. An aircraft
propellor work in one medium ... air. A boat propellor impacts two mediums ...
water and air (if you need confirmation of this, look astern of a boat
underway, under power ... you will see a wash/water, being lifted above the
surface in a rooster tail or lessor version thereof.
Now, go to a boatyard and stand in front of a propellor on some boat out of the
water.
Look at the angle/pitch of the blade, then start slowly rotating the blade
(assuming RH and you are standing in front of it) and visualize you are pushing
against water. As you rotate, (starting in the vertical up position) you will
note that the blade angle/pitch is pushing back and down against the water.
Water is not compressible. By pushing back and down, you are pushing against a
"solid" mass of water and are most efficient.
Now, as the propellor rotates it also pushes to the side against that "solid
mass of water, but as it starts rotating up, the solid mass becomes a relative
small column of water with air above it (air - highly compressible).
The propellor blade is now pushing back, but also up, and lifting that water up
and away - i.e., no longer a solid wall of water, into the air, and it becomes
less efficient.
The same applies as the blade re aproaches the vertical.
The forces of greatest efficiency are on the downward and sideward rotation of
the blade (pushing the stern to stbd when going ahead -left turn).
The same applies to backing, but because the prop is now pulling the boat, the
effect is far more noticeable.
Someone is bound to discuss the overhang of the hull, over the prop, should
negate this. Not so. That overhang is relatively short and variable, so that
although it may affect the degree, it will not stop the results.
BG And this is my theory and I'magonna stick to it......for now.

That theory sounds compelling at explaining a difference in the
efficiency of the blade during it's downward vs. upward travel (if
there's no overhang. This part of your explanation would create an
upward force. It would also create a listing torque force since the
upward force of your theory above is applied off the center of the prop.
But since the column of water is the same in both the sideways
directions, where does the sideways force come from to create prop walk?

Steve

On Sun, 6 Jun 2004 08:49:02 -0400, "Charles T. Low"
wrote:
The main effect is from the spiral prop wash. In reverse, where asymmetric
thrust is virtually always more pronounced, the top half of the prop wash
vortex strikes the hull, and pushes it sideways. The effect will vary
depending on the underwater hull shape, the angle of the prop shaft, design
of prop ...

So, a right hand propeller in reverse turns counter-clockwise. The top half
of the spiralling prop wash is moving to port, and pushes on the hull,
yawing the stern to port. The bottom half othe spiral is mostly in clear
water, pushing on nothing.

================================================== ====

Charles, I think you've got it, thanks.

JAXAshby could only repeat his infantile retort:

rickie, recess is over. go back to class.

What's the matter, Jax? Has Oz got you so whipped so badly over on the
siphon breaker thread that you can't even keep track of where you are
getting your ass kicked worse?

C'mon, Jax, don't be a Speedo Queen all your life, take a day off and
tell us all about your taildragger flying experiences and cite those
posts that you claim I made ...

Thom kicked your ass pretty good too, so maybe that's why you can only
come back with cut and pastes of your childish little hissy fit retorts.
This just hasn't been your week has it, Jax?

Historically this is where you fade away again ... good timing too, you
have done an excellent job showing all the new readers here just how
amazing you are.

Rick