Which way does a boat turn?
 

Simple question.

Q: Which way does the stern of a boat t-boned to a dock turn when, with the
rudder turned to port and the tranny in forward, you give a 2 second burst of
the engine?

A: I think we all agree the stern will move starboard.



Q: same question but rudder turned to starboard?

A: the stern will move to port.



Q: same question but rudder centered?

A: the stern will move to port due to prop walk



Q: same question, rudder centered, but tranny in reverse (bow of boat tied to
dock)?

A: the stern will move to port due to prop walk



Q: same question (tranny in reverse) but rudder to port?

A: the stern will move to port due to prop walk



Q: same question (tranny in reverse) but rudder to starboard?

A: the stern will move to port due to prop walk



Anybody but sherr doubt that? (forget the "good professor". he uses the word
"prop" when he means "rudder" and he wants to argue that friction in the rudder
bearing makes the difference)

Which way does a boat turn?
 

"T-boned to a dock"?

Assumptions:

1. You are describing a boat with a rh prop.

2. "T-boned to a dock" means the stem is jammed against the dock to prevent
forward movement.......(until the stern swings far enough that the angle is no
longer sufficient to brake the boat).

With those assumptions...........

Q: Which way does the stern of a boat t-boned to a dock turn when, with the
rudder turned to port and the tranny in forward, you give a 2 second burst of
the engine?

A: I think we all agree the stern will move starboard.

(you mean a two second application of forward gear, as the engine remains at
least idling, but otherwise......)

Correct.




Q: same question but rudder turned to starboard?

A: the stern will move to port.

Correct


Q: same question but rudder centered?

A: the stern will move to port due to prop walk

Incorrect. Here are some excerpts from my old copy of Chapman's. We can
probably assume that propellers still behave the way they did 20 years ago.

"Another factor also effects a boat's readtion to propeller rotation. While
this factgor is sometimes referred to as 'sideways blade pressure' it is more
properly an 'unequal blade thrust', exerted by the ascending and descending
blades of the propeller. Figure 709, top.

Here we are looking at the starboard side of a propeller shaft, inclined, as
most shafts are, at a significant angle to the water's surface and the the flow
of water past the blades. The actual pitch of the blades as manufactured, of
course, is the same, but the water flows diagonally across the plane in which
the blades revolve.

Figure 709 shows clearly how the effectof this is to increase the pitch of the
descending starboard blade, (right hand propeller) as compared with the
ascending port blade, when considered relative to the direction of water flow
past the propeller.

The importance of this factor is reduced as the shaft angle is decreased, and
naval architects sometimes take pains to have the engine installed as low as
possible to keep the shaft nearly parallel to the water's surface and to the
flow of water past the blades. This contributes to greater propeller eficiency,
and is a factor worth considering if it is consistent with other design
requirements. Once a boat is built, shaft angle is difficult, usually
impossible, to modify.

The relatively greater blade pitch on the starboard side creates a stronger
thrust on this side, causing the bow to turn to port.
As far as this single factor is concerned, THE STERN OF A SINGLE-SCREW BOAT
WITH A RIGHT-HAND PROPELLER
THUS NATURALLY TENDS TO GO TO STARBOARD WHEN THE PROPELLER IS GOING AHEAD, AND
TO PORT WHEN IT IS REVERSING."


Q: same question, rudder centered, but tranny in reverse (bow of boat tied to
dock)?

A: the stern will move to port due to prop walk


Correct.





Q: same question (tranny in reverse) but rudder to port?

A: the stern will move to port due to prop walk

Correct, particularly when the bow is secured to the dock and the vessel cannot
develop sternway.


Q: same question (tranny in reverse) but rudder to starboard?

A: the stern will move to port due to prop walk




Anybody but sherr doubt that?

Chapman's, for one.
According to an indpendent and recognized authority, you only missed one. That
gives you what, a strong B? :-)

Which way does a boat turn?
 

you are right, gould. prop walk in forward would be starboard because the prop
is turning cw as viewed from behind.

btw, Chapman's is correct as far as asym thrust is concerned, but end-plate
effect would add to the total lateral force.

assumptions as given, yes.


"T-boned to a dock"?

Assumptions:

1. You are describing a boat with a rh prop.

2. "T-boned to a dock" means the stem is jammed against the dock to prevent
forward movement.......(until the stern swings far enough that the angle is
no
longer sufficient to brake the boat).

With those assumptions...........

Q: Which way does the stern of a boat t-boned to a dock turn when, with the
rudder turned to port and the tranny in forward, you give a 2 second burst
of
the engine?

A: I think we all agree the stern will move starboard.

(you mean a two second application of forward gear, as the engine remains at
least idling, but otherwise......)

Correct.




Q: same question but rudder turned to starboard?

A: the stern will move to port.

Correct


Q: same question but rudder centered?

A: the stern will move to port due to prop walk

Incorrect. Here are some excerpts from my old copy of Chapman's. We can
probably assume that propellers still behave the way they did 20 years ago.

"Another factor also effects a boat's readtion to propeller rotation. While
this factgor is sometimes referred to as 'sideways blade pressure' it is
more
properly an 'unequal blade thrust', exerted by the ascending and descending
blades of the propeller. Figure 709, top.

Here we are looking at the starboard side of a propeller shaft, inclined, as
most shafts are, at a significant angle to the water's surface and the the
flow
of water past the blades. The actual pitch of the blades as manufactured, of
course, is the same, but the water flows diagonally across the plane in which
the blades revolve.

Figure 709 shows clearly how the effectof this is to increase the pitch of
the
descending starboard blade, (right hand propeller) as compared with the
ascending port blade, when considered relative to the direction of water flow
past the propeller.

The importance of this factor is reduced as the shaft angle is decreased, and
naval architects sometimes take pains to have the engine installed as low as
possible to keep the shaft nearly parallel to the water's surface and to the
flow of water past the blades. This contributes to greater propeller
eficiency,
and is a factor worth considering if it is consistent with other design
requirements. Once a boat is built, shaft angle is difficult, usually
impossible, to modify.

The relatively greater blade pitch on the starboard side creates a stronger
thrust on this side, causing the bow to turn to port.
As far as this single factor is concerned, THE STERN OF A SINGLE-SCREW BOAT
WITH A RIGHT-HAND PROPELLER
THUS NATURALLY TENDS TO GO TO STARBOARD WHEN THE PROPELLER IS GOING AHEAD,
AND
TO PORT WHEN IT IS REVERSING."


Q: same question, rudder centered, but tranny in reverse (bow of boat tied
to
dock)?

A: the stern will move to port due to prop walk


Correct.





Q: same question (tranny in reverse) but rudder to port?

A: the stern will move to port due to prop walk

Correct, particularly when the bow is secured to the dock and the vessel
cannot
develop sternway.


Q: same question (tranny in reverse) but rudder to starboard?

A: the stern will move to port due to prop walk




Anybody but sherr doubt that?

Chapman's, for one.
According to an indpendent and recognized authority, you only missed one.
That
gives you what, a strong B? :-)

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: (JAXAshby)
Date: 03/29/2004 15:02 Pacific Standard Time
Message-id:

Simple question.

Q: Which way does the stern of a boat t-boned to a dock turn when, with the
rudder turned to port and the tranny in forward, you give a 2 second burst of
the engine?

A: I think we all agree the stern will move starboard.



Q: same question but rudder turned to starboard?

A: the stern will move to port.



Q: same question but rudder centered?

A: the stern will move to port due to prop walk


Thats ok Jax .... we all understand you're a "newbie". Anyone with any
experience would have stated prop rotation, as it's important to the answers.
Just tell them you were using a left hand prop for the first set of questions
and a right hand for the second set of reverse questions.
BTW, you should also add that this exercise is without wind or current.
With wind or current, especially in the astern mode, depending on the boat,
things may not work according to Hoyle.

Shen

PS. It's up to a $1,000/hr .... I can see you'll need special handling, and I
'll have to waste 50 min out of every hour, just trying to keep you
concentrating.

Which way does a boat turn?
 

Give the dipsquat a break. He's still trying to "google" the
difference between inboard and outboard turning props on a twin screw
inboard ..... with no luck.

Shen44 wrote:
Subject: Which way does a boat turn?
From: (JAXAshby)
Date: 03/29/2004 15:02 Pacific Standard Time
Message-id:

Simple question.

Q: Which way does the stern of a boat t-boned to a dock turn when, with the
rudder turned to port and the tranny in forward, you give a 2 second burst of
the engine?

A: I think we all agree the stern will move starboard.



Q: same question but rudder turned to starboard?

A: the stern will move to port.



Q: same question but rudder centered?

A: the stern will move to port due to prop walk



Thats ok Jax .... we all understand you're a "newbie". Anyone with any
experience would have stated prop rotation, as it's important to the answers.
Just tell them you were using a left hand prop for the first set of questions
and a right hand for the second set of reverse questions.
BTW, you should also add that this exercise is without wind or current.
With wind or current, especially in the astern mode, depending on the boat,
things may not work according to Hoyle.

Shen

PS. It's up to a $1,000/hr .... I can see you'll need special handling, and I
'll have to waste 50 min out of every hour, just trying to keep you
concentrating.

Which way does a boat turn?
 

You STILL trying to figure that one out, Jax?

SV

Which way does a boat turn?
 

the rule is :a RH prop paddles to port in reverse. you figer the rest
rick

On 29 Mar 2004 23:02:24 GMT, JAXAshby wrote:

Simple question.

Q: Which way does the stern of a boat t-boned to a dock turn when, with
the
rudder turned to port and the tranny in forward, you give a 2 second
burst of
the engine?

A: I think we all agree the stern will move starboard.



Q: same question but rudder turned to starboard?

A: the stern will move to port.



Q: same question but rudder centered?

A: the stern will move to port due to prop walk



Q: same question, rudder centered, but tranny in reverse (bow of boat
tied to
dock)?

A: the stern will move to port due to prop walk



Q: same question (tranny in reverse) but rudder to port?

A: the stern will move to port due to prop walk



Q: same question (tranny in reverse) but rudder to starboard?

A: the stern will move to port due to prop walk



Anybody but sherr doubt that? (forget the "good professor". he uses the
word
"prop" when he means "rudder" and he wants to argue that friction in the
rudder
bearing makes the difference)



--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Which way does a boat turn?
 

JAXAshby wrote in message
...
you are right, gould. prop walk in forward would be starboard
because the prop
is turning cw as viewed from behind.

btw, Chapman's is correct as far as asym thrust is concerned,
but end-plate
effect would add to the total lateral force.

In your language - a flip flop?

I seem to remember about a week ago that I challenged your
explanation of prop walk (the aeronautical simile) with a bit of
trig to point out that the asymmetric thrust effect is
insignificant compared to hull interference (you call it end
plate effect?).

What I missed, in fact, is that it is even in the opposite sense!

JimB

Which way does a boat turn?
 

Perhaps a bit more food for thought?...

There are several effects that all contribute to prop walk (and I am
assured by an ex-Navy acquaintance that even ships with a horizontal
prop shaft still have prop walk). The one noted below (from Chapman)
may not be the best to use for THIS case.

Chapman's explanation here uses the incline of the prop shaft relative
to the flow of water past the blades. I believe this is meant to be
the angle between the inclined shaft and the HORIZONTAL flow of water
past the prop caused by the (forward) motion of the boat through the
water. (And this is confirmed by his later paragraph that explains why
engines are mounted lower to reduce this angle between the shaft and
(horizontal) flow of water past the prop.)

As the boat is jammed against the dock and not able to move through the
water there will be no horizontal flow of water due to forward motion.
The only flow past the prop will therefore probably be a flow parallel
to the shaft caused by the blades pushing the water in that direction
(possibly modified slightly by hull effects) and therefore the angle of
the ascending blade and the descending blade relative to this flow is
more nearly equal. In this case the difference in thrust from an
"ascending" vs a "descending" blade is probably minor and in fact the
concept of "ascending" and "descending" loses meaning if not referenced
to the horizontal in this case perhaps.

However the rotation of the prop is causing a swirling effect of the
water leaving the prop and the water leaving the ascending blade (on the
port side of the boat) may produce more push on the port side of the
hull than does the water swirling down from the descending blade (on the
starboard side) creating a net push on the port aft end of the boat,
adding to the turning effect to starboard. Note that if a single rudder
is mounted directly behind the prop the water hitting each side is
probably pretty equal - rather it is the water hitting whateve hull is
left in the way that probably has the greater effect and the water
corkscrewing away from the descending blade on the starboard side misses
the hull.

I have even heard the explanation that since the water is more dense at
the bottom of the rotation than at the top, the blade gets more "bight"
at the bottom of its swing and "rolls" the stern to starboard. Surely
this density difference is small so this contribution to the overall
effect from this must also be a minor part.

Dave

Gould 0738 wrote:

"T-boned to a dock"?

Assumptions:

1. You are describing a boat with a rh prop.

2. "T-boned to a dock" means the stem is jammed against the dock to prevent
forward movement.......(until the stern swings far enough that the angle is no
longer sufficient to brake the boat).

With those assumptions...........



Q: same question but rudder centered?

A: the stern will move to port due to prop walk

Incorrect. Here are some excerpts from my old copy of Chapman's. We can
probably assume that propellers still behave the way they did 20 years ago.

"Another factor also effects a boat's readtion to propeller rotation. While
this factgor is sometimes referred to as 'sideways blade pressure' it is more
properly an 'unequal blade thrust', exerted by the ascending and descending
blades of the propeller. Figure 709, top.

Here we are looking at the starboard side of a propeller shaft, inclined, as
most shafts are, at a significant angle to the water's surface and the the flow
of water past the blades. The actual pitch of the blades as manufactured, of
course, is the same, but the water flows diagonally across the plane in which
the blades revolve.

Figure 709 shows clearly how the effectof this is to increase the pitch of the
descending starboard blade, (right hand propeller) as compared with the
ascending port blade, when considered relative to the direction of water flow
past the propeller.

The importance of this factor is reduced as the shaft angle is decreased, and
naval architects sometimes take pains to have the engine installed as low as
possible to keep the shaft nearly parallel to the water's surface and to the
flow of water past the blades. This contributes to greater propeller eficiency,
and is a factor worth considering if it is consistent with other design
requirements. Once a boat is built, shaft angle is difficult, usually
impossible, to modify.

The relatively greater blade pitch on the starboard side creates a stronger
thrust on this side, causing the bow to turn to port.
As far as this single factor is concerned, THE STERN OF A SINGLE-SCREW BOAT
WITH A RIGHT-HAND PROPELLER
THUS NATURALLY TENDS TO GO TO STARBOARD WHEN THE PROPELLER IS GOING AHEAD, AND
TO PORT WHEN IT IS REVERSING."

Which way does a boat turn?
 

sherr wrote the following useful material:

Which way does a boat turn?
 

You STILL trying to figure that one out, Jax?

SV


which one is that?

Which way does a boat turn?
 

dave? not good.

ex-Navy acquaintance that even ships with a horizontal
prop shaft still have prop walk

end-plate effect

Chapman's explanation here uses the incline of the prop shaft relative
to the flow of water past the blades.

"asymetrical thrust" it is called, though Chapmans does not use the term

the inclined shaft and the HORIZONTAL flow of water
past the prop

doesn't have to horizontal, just has to different from the axis of the prop.

caused by the (forward) motion of the boat through the
water.

doesn't have to be from boat movement, just has to be water movement.

As the boat is jammed against the dock and not able to move through the
water there will be no horizontal flow of water due to forward motion.

no, the hull of the boat causes the water flow behind of the forward pushing
prop to "line up" not in line with the prop shaft, thus asym thrust.

The only flow past the prop will therefore probably be a flow parallel
to the shaft

no, the hul gets in the way, at least if the hull is anywhere near the prop

the water leaving the ascending blade (on the
port side of the boat) may produce more push on the port side of the
hull than does the water swirling down from the descending blade

why is this? what has "swirling" to do with it?

I have even heard the explanation that since the water is more dense at
the bottom of the rotation than at the top,

nah, the difference is virtually nothing. There is less than 1/2 psi pressure
difference per foot of water depth and water compresses
soooooooooooooooooooooooooooooo little than even several thousand psi wouldn't
make any difference.

Which way does a boat turn?
 

no, jim, what you see was quick typing on my part. "prop walk" is always to
port (on my boat, a rh prop) because I only worry about it when backing up.
Going forward I use the rudder to counter, something I can not do when backing
up until the boat is moving. I typed the tranny in forward and just typed prop
walk port. In forward, the prop walk is starboard.

quick typing, that's all. asym thrust is asym thrust. someone even quoted
Chapmans on the issue.

you are right, gould. prop walk in forward would be starboard
because the prop
is turning cw as viewed from behind.

btw, Chapman's is correct as far as asym thrust is concerned,
but end-plate
effect would add to the total lateral force.

In your language - a flip flop?

I seem to remember about a week ago that I challenged your
explanation of prop walk (the aeronautical simile) with a bit of
trig to point out that the asymmetric thrust effect is
insignificant compared to hull interference (you call it end
plate effect?).

What I missed, in fact, is that it is even in the opposite sense!

JimB

Which way does a boat turn?
 

"JAXAshby" wrote in message
...


Q: same question, rudder centered, but tranny in reverse (bow of boat tied
to
dock)?

A: the stern will move to port due to prop walk


I would have said to starboard, reason being that I would expect it to be
the opposite of the prop walk direction when in forward gear.

I have heard several different theories for "prop walk".

"Asymmetrical thrust" is certainly one, and obviously the one being debated
the most right now.

Cavitation is another. Consider that both surfaces of the prop are being
used. The "push" side of the prop can generate unlimited PSI, constrained
only by what can be delivered down the shaft and the strength of the prop
itself. The "Pull" side of the prop can only develop the pressure of the
ambient.

Consider a prop that is spinning just under the surface of the water. As
the tip of the blade passes over the top, the total pressure that can be
developed on the "pull" side is 14.7 PSI. (at the tip). As the tip of the
blade passes down the bottom side it is in deeper water, and hence will have
more ambient pressure. If the prop is 12 inches in diameter then it would
have a foots worth of water more pressure, or approximately another 1/2 PSI
or so. This difference in pressure top to bottom gives the bottom of the
prop just a little more bite, and the prop wants to walk.

There can be other reasons why a given boat kicks one way or the other.
Some inboards I have seen have the rudder mounted just off center, which
allows removal of the prop shaft without having to remove the rudder (which
it would hit if the rudder was on center). I would expect an off center
rudder to have some effect on prop walk.

What is the dominant effect? I have no clue. I don't care. I do know that
my single engine inboard is impossible to steer reliably in reverse. It
usually (but not always) kicks to port in reverse. Which is why when you see
me going down a tight fairway in the marina I will be hugging the left side
as I can turn right much better than I can turn left.

Rod McInnis

Which way does a boat turn?
 

On Tue, 30 Mar 2004 18:09:21 -0800, "Rod McInnis"
wrote:


"JAXAshby" wrote in message
...


Q: same question, rudder centered, but tranny in reverse (bow of boat tied
to
dock)?

A: the stern will move to port due to prop walk


I would have said to starboard, reason being that I would expect it to be
the opposite of the prop walk direction when in forward gear.

I have heard several different theories for "prop walk".

"Asymmetrical thrust" is certainly one, and obviously the one being debated
the most right now.

Cavitation is another. Consider that both surfaces of the prop are being
used. The "push" side of the prop can generate unlimited PSI, constrained
only by what can be delivered down the shaft and the strength of the prop
itself. The "Pull" side of the prop can only develop the pressure of the
ambient.

Consider a prop that is spinning just under the surface of the water. As
the tip of the blade passes over the top, the total pressure that can be
developed on the "pull" side is 14.7 PSI. (at the tip). As the tip of the
blade passes down the bottom side it is in deeper water, and hence will have
more ambient pressure. If the prop is 12 inches in diameter then it would
have a foots worth of water more pressure, or approximately another 1/2 PSI
or so. This difference in pressure top to bottom gives the bottom of the
prop just a little more bite, and the prop wants to walk.

There can be other reasons why a given boat kicks one way or the other.
Some inboards I have seen have the rudder mounted just off center, which
allows removal of the prop shaft without having to remove the rudder (which
it would hit if the rudder was on center). I would expect an off center
rudder to have some effect on prop walk.

What is the dominant effect? I have no clue. I don't care. I do know that
my single engine inboard is impossible to steer reliably in reverse. It
usually (but not always) kicks to port in reverse. Which is why when you see
me going down a tight fairway in the marina I will be hugging the left side
as I can turn right much better than I can turn left.


Our boat exhibits no prop walk that I can detect. It also can't steer
from propwash in forward. It must be moving for any steering to occur.
The prop (18-inch Martec) is 12 feet forward of the spade rudder and
fairly close to the keel, so it has little lever arm to turn the boat.

A friend has a boat (Bristol 35.5) that walks horribly. It has a
Maxprop that is much further aft than ours in a boat about the same
length. I suspect the Maxprop is set for excessive pitch, because it
doesn't produce much thrust, but walks like crazy.



Rodney Myrvaagnes NYC J36 Gjo/a

"WooWooism lives" Anon grafitto on the base of the Cuttyhunk breakwater light

Which way does a boat turn?
 

Comments interspersed:

Rod McInnis wrote:
"JAXAshby" wrote in message
...



Q: same question, rudder centered, but tranny in reverse (bow of boat tied

to

dock)?

A: the stern will move to port due to prop walk



I would have said to starboard, reason being that I would expect it to be
the opposite of the prop walk direction when in forward gear.

I believe he was talking about a RH, fixed pitch prop, no wind or
current.....stern should go to port in reverse, to stbd when ahead.

I have heard several different theories for "prop walk".

G Same here .... My opinion FWIW, prop walk is a function of the prop
and pitch. The angle of the shaft may increase it, but is not the basic
cause as will some hull shapes and prop locations (tunnels or nozzles),
increase or decrease it.....




There can be other reasons why a given boat kicks one way or the other.
Some inboards I have seen have the rudder mounted just off center, which
allows removal of the prop shaft without having to remove the rudder (which
it would hit if the rudder was on center). I would expect an off center
rudder to have some effect on prop walk.

My first impression is that this would have minimal effect if any, G
would need some test, and although I've worked some boats with various
rudders types and locations, I can't say that I've ever noticed a
difference that I could attribute to the rudder.


What is the dominant effect? I have no clue. I don't care. I do know that
my single engine inboard is impossible to steer reliably in reverse. It
usually (but not always) kicks to port in reverse.

Going to assume that you have a RH fixed pitch prop. This is the norm,
however, wind and/or current can make a boat which normally backs to
port because of the prop, back to stbd from the "get go".
Steering your boat "reliably" in reverse, would involve many possible
solutions, including "your boat just won't steer reliably in reverse".

Which is why when you see
me going down a tight fairway in the marina I will be hugging the left side
as I can turn right much better than I can turn left.

Interesting. Normally a single screw RH fixed pitch prop will steer more
easily to port than to stbd, unless you are talking a back and fill
turn, in which case you want to turn to stbd.

otn

Which way does a boat turn?
 

Rod,

Actually, the asymmetric response to forward and reverse can be used
to do some neat tricks (which I use all the time). Try this, next
time you're out in your boat with some time to spend:

Motor out to a bouy (navigation, crab pot, whatever) in open water,
where there's no current. The bouy doesn't have to be very close --
it's only to gauge forward motion.

Stop the boat, put the rudder hard over to starboard, put the motor in
forward, and gun it. The first reaction will be that the stern kicks
to port. The next will be that the boat starts to move forward.

Immediately put the motor in reverse, LEAVING THE RUDDER HARD TO
STARBOARD. Apply moderate juice. The stern will continue to move to
port, and eventually the boat will come to a stop. Keep reversing,
and the stern will continue to move to port, due to the effects that
have been described already in this thread. Note where the boat is
with respect to the buoy, and continue backing until you've canceled
any forward motion and she's back where she started.

Now put the motor in forward and repeat the whole operation. With a
little practice, you can almost eliminate all the forward and aft
motions, and simply turn the boat inside her own length, by simply
pushing the stick forward and back, all the while holding the rudder
hard over. When you need to do this in close quarters (say, in a
marina with only a foot or two of room between your bow and the boat
ahead of you, and between your stern and the boat astern), you will
draw applause from onlookers.

Now, suppose some day you need to turn the boat in the opposite
direction, say, 90 degrees. Is there a similar way to turn her inside
her length, but in the opposite direction? No. So, simply turn her
the 270 degrees the way she wants to go (clockwise) until you've
accomplished the turn you need! Big ships do this all the time, and
it works great.

So no need ever again to hug the port side of your channel!

"Rod McInnis" wrote in message ...
"JAXAshby" wrote in message
...


Q: same question, rudder centered, but tranny in reverse (bow of boat tied
to
dock)?

A: the stern will move to port due to prop walk


I would have said to starboard, reason being that I would expect it to be
the opposite of the prop walk direction when in forward gear.

I have heard several different theories for "prop walk".

"Asymmetrical thrust" is certainly one, and obviously the one being debated
the most right now.

Cavitation is another. Consider that both surfaces of the prop are being
used. The "push" side of the prop can generate unlimited PSI, constrained
only by what can be delivered down the shaft and the strength of the prop
itself. The "Pull" side of the prop can only develop the pressure of the
ambient.

Consider a prop that is spinning just under the surface of the water. As
the tip of the blade passes over the top, the total pressure that can be
developed on the "pull" side is 14.7 PSI. (at the tip). As the tip of the
blade passes down the bottom side it is in deeper water, and hence will have
more ambient pressure. If the prop is 12 inches in diameter then it would
have a foots worth of water more pressure, or approximately another 1/2 PSI
or so. This difference in pressure top to bottom gives the bottom of the
prop just a little more bite, and the prop wants to walk.

There can be other reasons why a given boat kicks one way or the other.
Some inboards I have seen have the rudder mounted just off center, which
allows removal of the prop shaft without having to remove the rudder (which
it would hit if the rudder was on center). I would expect an off center
rudder to have some effect on prop walk.

What is the dominant effect? I have no clue. I don't care. I do know that
my single engine inboard is impossible to steer reliably in reverse. It
usually (but not always) kicks to port in reverse. Which is why when you see
me going down a tight fairway in the marina I will be hugging the left side
as I can turn right much better than I can turn left.

Rod McInnis

Which way does a boat turn?
 

Our boat exhibits no prop walk that I can detect. It also can't steer
from propwash in forward. It must be moving for any steering to occur.
The prop (18-inch Martec) is 12 feet forward of the spade rudder and
fairly close to the keel, so it has little lever arm to turn the boat.

yeah, 12 feet doesn't leave much "push" still in the prop stream, and too a
prop at about the pivot point can't do much twisting of the boat.

Which way does a boat turn?
 

My opinion FWIW, prop walk is a function of the prop
and pitch.

owners of AutoProps report limited prop walk as compared to their prior fixed
blade props. AutoProp blades continuously change pitch during a rotation so
that (more or less) total thrust on each side of the prop rev is the same.

Which way does a boat turn?
 

I think you missed my point. I wasn't arguing with the basics of the
discussion - just suggesting the Chapman-described reason may not be the
strongest component in this case.

JAXAshby wrote:

dave? not good.

Which part? Seems like we are in agreement more than we differ!


ex-Navy acquaintance that even ships with a horizontal
prop shaft still have prop walk

end-plate effect


But still an existing effect whatever you call it and different than
what was attributed in the mentioned Chapman's discussion?


Chapman's explanation here uses the incline of the prop shaft relative
to the flow of water past the blades.

"asymetrical thrust" it is called, though Chapmans does not use the term


"A rose by any other name"? I didn't argue that if water passes over
the prop at an angle to the shaft (by whatever cause) this effect will
occur. But if water flow is exactly parallel to the shaft (very
unlikely I agree) no SUCH effect would occur. (The other effects that
cause prop walk would then become more significant in this unlikely situation.)



the inclined shaft and the HORIZONTAL flow of water
past the prop

doesn't have to horizontal, just has to different from the axis of the prop.


Again, I agree but I was discussing the suitability of the use of
Chapman's words and he (was quoted in the proceeding discussion to have)
used the term "parallel to the water's surface and to the flow of water
past the blades" (which implies the flow of water is horizontal, because
the shaft could never be parallel to the water's surface and to the flow
of water at the same time if the flow of water he (Chapman) is referring
to here isn't parallel to the water's surface - which is assumed to be
horizontal in most simple cases!)



caused by the (forward) motion of the boat through the
water.

doesn't have to be from boat movement, just has to be water movement.

So I trust you are not adding a new "fact" to the original discussion -
that the boat is tied to the dock but there is a current flowing past
the dock and the boat? Why not add that there is a current parallel to
the dock pushing the stern to port or to starboard? I think the
original description would imply the boat and dock are in still water.
However if the "water movement" you refer to is just from the prop, I
think I covered that... (see below)


As the boat is jammed against the dock and not able to move through the
water there will be no horizontal flow of water due to forward motion.

no, the hull of the boat causes the water flow behind of the forward pushing
prop to "line up" not in line with the prop shaft, thus asym thrust.


Again, see below. You left off part of my comment on this!


The only flow past the prop will therefore probably be a flow parallel
to the shaft

no, the hul gets in the way, at least if the hull is anywhere near the prop


You ignored a significant part of my statement: "(possibly modified
slightly by hull effects)" so in fact we are in agreement here.



the water leaving the ascending blade (on the
port side of the boat) may produce more push on the port side of the
hull than does the water swirling down from the descending blade

why is this? what has "swirling" to do with it?


The water leaves the prop in a sort of corkscrew fashion - that which
leaves the descending starboard blade will tend to corkscrew downward
and back away from the hull. That which leaves the ascending port blade
will corkscrew upward and back tending to cause a net push on the aft
sections of the hull.



I have even heard the explanation that since the water is more dense at
the bottom of the rotation than at the top,

nah, the difference is virtually nothing. There is less than 1/2 psi pressure
difference per foot of water depth and water compresses
soooooooooooooooooooooooooooooo little than even several thousand psi wouldn't
make any difference.


And again aren't you just agreeing with me? ("Surely this density
difference is small so this contribution to the overall effect from this
must also be a minor part.")

All I was trying to get across is that the effects causing prop walk are
multiple and in varying degrees and in the specific setup originally
described (tied bow to dock) attributing the action to one single effect
(the mentioned Chapman explanation) may not be fully justified.

I am sure we can both agree that to most boaters knowing the Physics
behind these effects is really unnecessary. Knowing what boat will do
in each situation and being able to use it to safely and effectivly
control the boat in a tight location is the thing!

Dave

Which way does a boat turn?
 

"Rodney Myrvaagnes" wrote in message
...

Our boat exhibits no prop walk that I can detect. It also can't steer
from propwash in forward. It must be moving for any steering to occur.
The prop (18-inch Martec) is 12 feet forward of the spade rudder and
fairly close to the keel, so it has little lever arm to turn the boat.

I assume that this is a sail boat, which would put this into a "large
rudder" catagory. Sailboats, by their very nature, need to be able to steer
at slow speeds without any thrust from the prop. Thus, they install a rudder
that is large enough to provide adequate steering at dead slow speeds.

A typical power boat, on the other hand, uses a very small rudder that is
located as close as possible to the prop. The rudder is rarely taller than
the prop is. Such a rudder is very effective when it can deflect the stream
of water that is being pushed by the prop, but has minimal effect when the
prop is not turning.


Rod

Which way does a boat turn?
 

comments intersperced

end-plate effect


But still an existing effect whatever you call it and different than
what was attributed in the mentioned Chapman's discussion?

yes, different. end-plate effect means the thrust is greater for the blade tip
coming "close" ("close" is a variable term) to an end plate, which constrains
the flow.

"asymetrical thrust" it is called, though Chapmans does not use the term


"A rose by any other name"?

it is a common term, though Chapmans didn't use it.

But if water flow is exactly parallel to the shaft (very
unlikely I agree) no SUCH effect would occur.

true.

doesn't have to horizontal, just has to different from the axis of the
prop.


Again, I agree but I was discussing the suitability of the use of
Chapman's words and he (was quoted in the proceeding discussion to have)
used the term "parallel to the water's surface and to the flow of water
past the blades" (which implies the flow of water is horizontal, because
the shaft could never be parallel to the water's surface and to the flow
of water at the same time if the flow of water he (Chapman) is referring
to here isn't parallel to the water's surface - which is assumed to be
horizontal in most simple cases!)

Chapmans described the effects of a downward slanting propshaft. It seemed
some people were under the impression that that was the only issue. End plate
effect is another and different issue issue.


caused by the (forward) motion of the boat through the
water.

doesn't have to be from boat movement, just has to be water movement.

So I trust you are not adding a new "fact" to the original discussion -
that the boat is tied to the dock but there is a current flowing past
the dock and the boat?

assumption was that no current existed outside that which the prop caused.

Why not add that there is a current parallel to
the dock pushing the stern to port or to starboard? I think the
original description would imply the boat and dock are in still water.

yes.

However if the "water movement" you refer to is just from the prop, I
think I covered that... (see below)


As the boat is jammed against the dock and not able to move through the
water there will be no horizontal flow of water due to forward motion.

no, the hull of the boat causes the water flow behind of the forward
pushing
prop to "line up" not in line with the prop shaft, thus asym thrust.


Again, see below. You left off part of my comment on this!

I did see the comment and thought I was expanding it. sorry if my words did
not convey that.


The only flow past the prop will therefore probably be a flow parallel
to the shaft

no, the hul gets in the way, at least if the hull is anywhere near the prop


You ignored a significant part of my statement: "(possibly modified
slightly by hull effects)" so in fact we are in agreement here.



the water leaving the ascending blade (on the
port side of the boat) may produce more push on the port side of the
hull than does the water swirling down from the descending blade

why is this? what has "swirling" to do with it?


The water leaves the prop in a sort of corkscrew fashion - that which
leaves the descending starboard blade will tend to corkscrew downward
and back away from the hull. That which leaves the ascending port blade
will corkscrew upward and back tending to cause a net push on the aft
sections of the hull.

you have mostly described "end plate" effect, though end plate effect has more
implications.


I have even heard the explanation that since the water is more dense at
the bottom of the rotation than at the top,

nah, the difference is virtually nothing. There is less than 1/2 psi
pressure
difference per foot of water depth and water compresses
soooooooooooooooooooooooooooooo little than even several thousand psi
wouldn't
make any difference.


And again aren't you just agreeing with me? ("Surely this density
difference is small so this contribution to the overall effect from this
must also be a minor part.")

it is hard to say it has even a minor part. the density of water is for all
practical purposes the same at any depth.


All I was trying to get across is that the effects causing prop walk are
multiple and in varying degrees and in the specific setup originally
described (tied bow to dock) attributing the action to one single effect
(the mentioned Chapman explanation) may not be fully justified.

I agree. end plate effect is also an issue.


I am sure we can both agree that to most boaters knowing the Physics
behind these effects is really unnecessary. Knowing what boat will do
in each situation and being able to use it to safely and effectivly
control the boat in a tight location is the thing!

I brought it up because I have found that most boaters think a blast of the
engine in reverse will affect the rudder. I have also seen boaters who were
told by marinas to spend major bux to move a prop back closer to the rudder to
"help fix" the lack of rudder response backing up. Ya gotta have a boat moving
backwards through the water to have the rudder effective.


Dave

Which way does a boat turn?
 

"Rob Overton" wrote in message
om...


Actually, the asymmetric response to forward and reverse can be used
to do some neat tricks (which I use all the time). Try this, next
time you're out in your boat with some time to spend:

Oh, I have have operated single engine inboards for 25 years. Believe me, I
am quite familiar with the tricks.




Now put the motor in forward and repeat the whole operation. With a
little practice, you can almost eliminate all the forward and aft
motions, and simply turn the boat inside her own length, by simply
pushing the stick forward and back, all the while holding the rudder
hard over.


The degree to which this works varies greatly with the boat and conditions.

15 years ago I owned a 1956 Stephens, a wooden hull boat with a single
inboard. This boat actually had a sizable keel, about an 18 x 4 inch timber
that hung down below the hull. The keel prevented excessive lateral motion
while allowing the boat to pivot.

I also owned a 1979 Pro Am tournament ski boat, inboard. This was a fairly
small boat with the engine mounted center. Its light weight and bulk of the
mass in the center would also make it want to pivot more about the center.
The 2000 Air Nautique that replaced it was similar. Also a center mounted
engine, but the boat was bigger and heavier, much more sluggish. It would
not pivot inside its own length, but it was close.

My current inboard is a 2003 Super Air Nautique. This is a V-drive inboard,
which puts the engine in the back. It is even a bigger and heavier boat.
Having the bulk of the weight in the very back makes the boat very sluggish
to turn. It doesn't pivot, it turns. It turns slightly better to the right
when going forward, and reverse tends to make the stern push to port so if
the channel is narrow I will make my turns that direction.

Add on top of this wind and current. If I was on a lake on a windless day I
could manage just about anything. I boat mostly on the California delta,
and have wind and tidal currents to deal with. I may have to contend with a
2 knot current pushing me one way while a 10 knot wind is pushing me a
different direction. Sometimes the current swirls around and totally messes
things up. The wind is always confused as it deflects off of covered docks
and the levee.


Rod

Which way does a boat turn?
 

On Wed, 31 Mar 2004 11:56:00 -0800, "Rod McInnis"
wrote:


"Rodney Myrvaagnes" wrote in message
.. .

Our boat exhibits no prop walk that I can detect. It also can't steer
from propwash in forward. It must be moving for any steering to occur.
The prop (18-inch Martec) is 12 feet forward of the spade rudder and
fairly close to the keel, so it has little lever arm to turn the boat.

I assume that this is a sail boat, which would put this into a "large
rudder" catagory. Sailboats, by their very nature, need to be able to steer
at slow speeds without any thrust from the prop. Thus, they install a rudder
that is large enough to provide adequate steering at dead slow speeds.

A typical power boat, on the other hand, uses a very small rudder that is
located as close as possible to the prop. The rudder is rarely taller than
the prop is. Such a rudder is very effective when it can deflect the stream
of water that is being pushed by the prop, but has minimal effect when the
prop is not turning.

Yes, ours is a sailboat. We rented a canal boat once that had a
semibalanced barn door rudder clost to the prop. It could turn
practically in its own length. The appearance of the propwash suggests
the rudder completely covered the prop circle, shooting out the side
when hard over.



In reverse it did walk, but very predictably. As icing on the cake, it
also had a bow thruster.
Rod



Rodney Myrvaagnes NYC J36 Gjo/a


"Curse thee, thou quadrant. No longer will I guide my earthly way by thee." Capt. Ahab

Which way does a boat turn?
 

Being old and senile, I have to work things out with a mind
picture.

Re prop-walk...if I have a prop with flat blades aligned fore
and aft, I essentially have a "paddle wheel". If I turn the prop
clock-wise (as viewed from the rear of the boat), I'd
expect the stern to go to the right. Reversing the direction
would obviously make the stern go to the left.

If I re-pitch the prop so the flat blades are at right angles to the keel,
(cross-ways), I'd expect a bit of froth, but not much in the way of
stern reaction.

When I consider a *real* prop, the blades are aligned between
the two extremes above, and I'd expect the stern reaction to
also be between the two extremes.

Norm B

Which way does a boat turn?
 

Being old and senile, I have to work things out with a mind
picture.

Re prop-walk...if I have a prop with flat blades aligned fore
and aft, I essentially have a "paddle wheel". If I turn the prop
clock-wise (as viewed from the rear of the boat), I'd
expect the stern to go to the right. Reversing the direction
would obviously make the stern go to the left.

If I re-pitch the prop so the flat blades are at right angles to the keel,
(cross-ways), I'd expect a bit of froth, but not much in the way of
stern reaction.

When I consider a *real* prop, the blades are aligned between
the two extremes above, and I'd expect the stern reaction to
also be between the two extremes.

Norm B

Which way does a boat turn?
 

A paddle wheel has it's top portion out of the water, a prop doesn't.


"engsol" wrote in message
...
Being old and senile, I have to work things out with a mind
picture.

Re prop-walk...if I have a prop with flat blades aligned fore
and aft, I essentially have a "paddle wheel". If I turn the prop
clock-wise (as viewed from the rear of the boat), I'd
expect the stern to go to the right. Reversing the direction
would obviously make the stern go to the left.

If I re-pitch the prop so the flat blades are at right angles to the keel,
(cross-ways), I'd expect a bit of froth, but not much in the way of
stern reaction.

When I consider a *real* prop, the blades are aligned between
the two extremes above, and I'd expect the stern reaction to
also be between the two extremes.

Norm B

Which way does a boat turn?
 

A paddle wheel has it's top portion out of the water, a prop doesn't.


"engsol" wrote in message
...
Being old and senile, I have to work things out with a mind
picture.

Re prop-walk...if I have a prop with flat blades aligned fore
and aft, I essentially have a "paddle wheel". If I turn the prop
clock-wise (as viewed from the rear of the boat), I'd
expect the stern to go to the right. Reversing the direction
would obviously make the stern go to the left.

If I re-pitch the prop so the flat blades are at right angles to the keel,
(cross-ways), I'd expect a bit of froth, but not much in the way of
stern reaction.

When I consider a *real* prop, the blades are aligned between
the two extremes above, and I'd expect the stern reaction to
also be between the two extremes.

Norm B

Which way does a boat turn?
 

Lower that paddle wheel into the water, until it is just beneath the
water .... bet it will still pull to the right, because the blades on
the upward part of the rotation will be lifting the water and basically
throwing the "push" away (into the air) i.e., they'll be pushing, but
not at the efficiency of the blades on the downward turn.

otn

Scott Vernon wrote:
A paddle wheel has it's top portion out of the water, a prop doesn't.


"engsol" wrote in message
...

Being old and senile, I have to work things out with a mind
picture.

Re prop-walk...if I have a prop with flat blades aligned fore
and aft, I essentially have a "paddle wheel". If I turn the prop
clock-wise (as viewed from the rear of the boat), I'd
expect the stern to go to the right. Reversing the direction
would obviously make the stern go to the left.

If I re-pitch the prop so the flat blades are at right angles to the keel,
(cross-ways), I'd expect a bit of froth, but not much in the way of
stern reaction.

When I consider a *real* prop, the blades are aligned between
the two extremes above, and I'd expect the stern reaction to
also be between the two extremes.

Norm B

Which way does a boat turn?
 

Lower that paddle wheel into the water, until it is just beneath the
water .... bet it will still pull to the right, because the blades on
the upward part of the rotation will be lifting the water and basically
throwing the "push" away (into the air) i.e., they'll be pushing, but
not at the efficiency of the blades on the downward turn.

otn

Scott Vernon wrote:
A paddle wheel has it's top portion out of the water, a prop doesn't.


"engsol" wrote in message
...

Being old and senile, I have to work things out with a mind
picture.

Re prop-walk...if I have a prop with flat blades aligned fore
and aft, I essentially have a "paddle wheel". If I turn the prop
clock-wise (as viewed from the rear of the boat), I'd
expect the stern to go to the right. Reversing the direction
would obviously make the stern go to the left.

If I re-pitch the prop so the flat blades are at right angles to the keel,
(cross-ways), I'd expect a bit of froth, but not much in the way of
stern reaction.

When I consider a *real* prop, the blades are aligned between
the two extremes above, and I'd expect the stern reaction to
also be between the two extremes.

Norm B

Which way does a boat turn?
 

nah.

Lower that paddle wheel into the water, until it is just beneath the
water .... bet it will still pull to the right, because the blades on
the upward part of the rotation will be lifting the water and basically
throwing the "push" away (into the air) i.e., they'll be pushing, but
not at the efficiency of the blades on the downward turn.

otn

Scott Vernon wrote:
A paddle wheel has it's top portion out of the water, a prop doesn't.


"engsol" wrote in message
...

Being old and senile, I have to work things out with a mind
picture.

Re prop-walk...if I have a prop with flat blades aligned fore
and aft, I essentially have a "paddle wheel". If I turn the prop
clock-wise (as viewed from the rear of the boat), I'd
expect the stern to go to the right. Reversing the direction
would obviously make the stern go to the left.

If I re-pitch the prop so the flat blades are at right angles to the keel,
(cross-ways), I'd expect a bit of froth, but not much in the way of
stern reaction.

When I consider a *real* prop, the blades are aligned between
the two extremes above, and I'd expect the stern reaction to
also be between the two extremes.

Norm B

Which way does a boat turn?
 

nah.

Lower that paddle wheel into the water, until it is just beneath the
water .... bet it will still pull to the right, because the blades on
the upward part of the rotation will be lifting the water and basically
throwing the "push" away (into the air) i.e., they'll be pushing, but
not at the efficiency of the blades on the downward turn.

otn

Scott Vernon wrote:
A paddle wheel has it's top portion out of the water, a prop doesn't.


"engsol" wrote in message
...

Being old and senile, I have to work things out with a mind
picture.

Re prop-walk...if I have a prop with flat blades aligned fore
and aft, I essentially have a "paddle wheel". If I turn the prop
clock-wise (as viewed from the rear of the boat), I'd
expect the stern to go to the right. Reversing the direction
would obviously make the stern go to the left.

If I re-pitch the prop so the flat blades are at right angles to the keel,
(cross-ways), I'd expect a bit of froth, but not much in the way of
stern reaction.

When I consider a *real* prop, the blades are aligned between
the two extremes above, and I'd expect the stern reaction to
also be between the two extremes.

Norm B

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: (JAXAshby)

nah.

yah .... two for and one against ....G anyone else?


Lower that paddle wheel into the water, until it is just beneath the
water .... bet it will still pull to the right, because the blades on
the upward part of the rotation will be lifting the water and basically
throwing the "push" away (into the air) i.e., they'll be pushing, but
not at the efficiency of the blades on the downward turn.

otn

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: (JAXAshby)

nah.

yah .... two for and one against ....G anyone else?


Lower that paddle wheel into the water, until it is just beneath the
water .... bet it will still pull to the right, because the blades on
the upward part of the rotation will be lifting the water and basically
throwing the "push" away (into the air) i.e., they'll be pushing, but
not at the efficiency of the blades on the downward turn.

otn

Which way does a boat turn?
 

sherr, did you really wish to say water displaced one way is more important
than water displaced another way?

You did. okay, you have just invented the Perpetual Motion Machine. Don't
forget the Patent Offices requires a working model before you submit an
application.

nah.

yah .... two for and one against ....G anyone else?


Lower that paddle wheel into the water, until it is just beneath the
water .... bet it will still pull to the right, because the blades on
the upward part of the rotation will be lifting the water and basically
throwing the "push" away (into the air) i.e., they'll be pushing, but
not at the efficiency of the blades on the downward turn.

otn

Which way does a boat turn?
 

sherr, did you really wish to say water displaced one way is more important
than water displaced another way?

You did. okay, you have just invented the Perpetual Motion Machine. Don't
forget the Patent Offices requires a working model before you submit an
application.

nah.

yah .... two for and one against ....G anyone else?


Lower that paddle wheel into the water, until it is just beneath the
water .... bet it will still pull to the right, because the blades on
the upward part of the rotation will be lifting the water and basically
throwing the "push" away (into the air) i.e., they'll be pushing, but
not at the efficiency of the blades on the downward turn.

otn

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: (JAXAshby)
Date: 04/01/2004 16:59 Pacific Standard Time
Message-id:

sherr, did you really wish to say water displaced one way is more important
than water displaced another way?

Nope....and didn't, neither.

jexer, did you really wish to say that, that paddle wheel (just below the
surface) was working in a solid medium of water through all angles of rotation,
thusly exerting the same amount of push/pull on a hull, at all angles of
rotation?
You did ..... interesting....

Sherr ( I guess I'm not schlackoff this week .... never know which name I'm
s'posed to use wid der jexer, errr, jaxer, errrr jaxass.....whatever)

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: (JAXAshby)
Date: 04/01/2004 16:59 Pacific Standard Time
Message-id:

sherr, did you really wish to say water displaced one way is more important
than water displaced another way?

Nope....and didn't, neither.

jexer, did you really wish to say that, that paddle wheel (just below the
surface) was working in a solid medium of water through all angles of rotation,
thusly exerting the same amount of push/pull on a hull, at all angles of
rotation?
You did ..... interesting....

Sherr ( I guess I'm not schlackoff this week .... never know which name I'm
s'posed to use wid der jexer, errr, jaxer, errrr jaxass.....whatever)

Which way does a boat turn?
 

sherr, ever hear "For each action there is an equal and opposite reaction"?

if you have, why do you seem to think it doesn't apply underwater?

Subject: Which way does a boat turn?
From: (JAXAshby)
Date: 04/01/2004 16:59 Pacific Standard Time
Message-id:

sherr, did you really wish to say water displaced one way is more important
than water displaced another way?

Nope....and didn't, neither.

jexer, did you really wish to say that, that paddle wheel (just below the
surface) was working in a solid medium of water through all angles of
rotation,
thusly exerting the same amount of push/pull on a hull, at all angles of
rotation?
You did ..... interesting....

Sherr ( I guess I'm not schlackoff this week .... never know which name I'm
s'posed to use wid der jexer, errr, jaxer, errrr jaxass.....whatever)

Which way does a boat turn?
 

sherr, ever hear "For each action there is an equal and opposite reaction"?

if you have, why do you seem to think it doesn't apply underwater?

Subject: Which way does a boat turn?
From: (JAXAshby)
Date: 04/01/2004 16:59 Pacific Standard Time
Message-id:

sherr, did you really wish to say water displaced one way is more important
than water displaced another way?

Nope....and didn't, neither.

jexer, did you really wish to say that, that paddle wheel (just below the
surface) was working in a solid medium of water through all angles of
rotation,
thusly exerting the same amount of push/pull on a hull, at all angles of
rotation?
You did ..... interesting....

Sherr ( I guess I'm not schlackoff this week .... never know which name I'm
s'posed to use wid der jexer, errr, jaxer, errrr jaxass.....whatever)