Which way does a boat turn?
 

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


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

Yup. I think it's basic physics ....larn't it in gramma school.

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

hmmm let me try and draw a pitcher fer ya.
Your looking at this here paddle wheel just beneath the surface of the water
(totally submerged), from the side, which is rotating clockwise through 360
deg.
It is being driven by a shaft coming out the stern of a boat, longitudinally,
and the whole paddlewheel is located just aft of the transom. (kinda like a RH
paddlewheel).
Now, are you trying to tell me that the amount of "push" that these paddles
develope against the boat, is the same between 090 and 180 deg. rotation as it
is between 270 and 360 deg ?

Shen

Which way does a boat turn?
 

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


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

Yup. I think it's basic physics ....larn't it in gramma school.

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

hmmm let me try and draw a pitcher fer ya.
Your looking at this here paddle wheel just beneath the surface of the water
(totally submerged), from the side, which is rotating clockwise through 360
deg.
It is being driven by a shaft coming out the stern of a boat, longitudinally,
and the whole paddlewheel is located just aft of the transom. (kinda like a RH
paddlewheel).
Now, are you trying to tell me that the amount of "push" that these paddles
develope against the boat, is the same between 090 and 180 deg. rotation as it
is between 270 and 360 deg ?

Shen

Which way does a boat turn?
 

"Shen44" wrote

hmmm let me try and draw a pitcher fer ya.
Your looking at this here paddle wheel just beneath the surface of the
water
(totally submerged), from the side, which is rotating clockwise through
360
deg.
It is being driven by a shaft coming out the stern of a boat,
longitudinally,
and the whole paddlewheel is located just aft of the transom. (kinda like
a RH
paddlewheel).
Now, are you trying to tell me that the amount of "push" that these
paddles
develope against the boat, is the same between 090 and 180 deg. rotation
as it
is between 270 and 360 deg ?

I would guess yes. But I don't know. And I was picturing a side wheeler.

Sv

Which way does a boat turn?
 

"Shen44" wrote

hmmm let me try and draw a pitcher fer ya.
Your looking at this here paddle wheel just beneath the surface of the
water
(totally submerged), from the side, which is rotating clockwise through
360
deg.
It is being driven by a shaft coming out the stern of a boat,
longitudinally,
and the whole paddlewheel is located just aft of the transom. (kinda like
a RH
paddlewheel).
Now, are you trying to tell me that the amount of "push" that these
paddles
develope against the boat, is the same between 090 and 180 deg. rotation
as it
is between 270 and 360 deg ?

I would guess yes. But I don't know. And I was picturing a side wheeler.

Sv

Which way does a boat turn?
 

It would appear that Shen is replacing the prop of a boat with a
paddle wheel and locating it aft of the transom, as a follow up to
someone else's post, using the paddlewheel. However, in his example a
side-wheeler would work as long as you submerge the entire wheel.
Can you explain why the force exerted by the blades at those angles
would be equal....though opposite?

otn

Scott Vernon wrote:
"Shen44" wrote

hmmm let me try and draw a pitcher fer ya.
Your looking at this here paddle wheel just beneath the surface of the

water

(totally submerged), from the side, which is rotating clockwise through

360

deg.
It is being driven by a shaft coming out the stern of a boat,

longitudinally,

and the whole paddlewheel is located just aft of the transom. (kinda like

a RH

paddlewheel).
Now, are you trying to tell me that the amount of "push" that these

paddles

develope against the boat, is the same between 090 and 180 deg. rotation

as it

is between 270 and 360 deg ?


I would guess yes. But I don't know. And I was picturing a side wheeler.

Sv

Which way does a boat turn?
 

It would appear that Shen is replacing the prop of a boat with a
paddle wheel and locating it aft of the transom, as a follow up to
someone else's post, using the paddlewheel. However, in his example a
side-wheeler would work as long as you submerge the entire wheel.
Can you explain why the force exerted by the blades at those angles
would be equal....though opposite?

otn

Scott Vernon wrote:
"Shen44" wrote

hmmm let me try and draw a pitcher fer ya.
Your looking at this here paddle wheel just beneath the surface of the

water

(totally submerged), from the side, which is rotating clockwise through

360

deg.
It is being driven by a shaft coming out the stern of a boat,

longitudinally,

and the whole paddlewheel is located just aft of the transom. (kinda like

a RH

paddlewheel).
Now, are you trying to tell me that the amount of "push" that these

paddles

develope against the boat, is the same between 090 and 180 deg. rotation

as it

is between 270 and 360 deg ?


I would guess yes. But I don't know. And I was picturing a side wheeler.

Sv

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: "Scott Vernon"

I would guess yes. But I don't know. And I was picturing a side wheeler.

Sv

Ok, continue to picture a sidewheeler.
Now, in hopes of further clarifying what I'm trying to describe, the
paddlewheel is 6' in diameter and you totally submerge it to a point, say, 6"
beneath the water.
Your boat is floating in 200' of water with no land in sight (i.e., you've just
got water with the earth beneath it and water with air, 6" above it).
Looking at the "wheel" from the side and starting at a rotation angle of 090,
as the blade of the wheel rotates clockwise to 180 deg, it is pushing down and
to the left, against a solid non compressible column of water, 200ish feet deep
(it's working as efficiently as it can) and pulling the boat to your right.
Now look at the blades in the opposite quadrant (270 - 360). Starting at 270
and rotating towards 360, the blades are pushing up and to the right, against
........ a 3' 6" column of water with nothing but good old compressible air
above. What happens?
Basically the blades lift that column of water and throw it away into the air,
losing a high percentage of their efficiency to pull down and to the left,
compared to their opposite quadrant.
If you look at 000 - 090, compared to 180 -270, you will see a different set of
comparisons, but I'd bet the net result would still be a greater pull/push to
the right.
Finally, go to a boatyard and look at a power boat on the "hard". Stand in
front of the propellor and pick one blade. Assuming RH, rotate the blade
counter clockwise and as you do, sight 90 deg to the blade pitch and visualize
the direction that the blade will "push" the water. I think you notice that the
blade will be pushing water up, on it's upward swing (into the air), thus
losing efficiency and the net effect will be a pull to the right (your left
standing in front of the prop) .......propwalk.
I don't doubt there are some possible flaws in this description, but it's how I
visualize the overall effect and cause of propwalk.
BTW, propwalk is just as important with twin screw. It's why a twin screw with
inboard turning props handles so much differently as one with outboard turning
props.

Shen

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: "Scott Vernon"

I would guess yes. But I don't know. And I was picturing a side wheeler.

Sv

Ok, continue to picture a sidewheeler.
Now, in hopes of further clarifying what I'm trying to describe, the
paddlewheel is 6' in diameter and you totally submerge it to a point, say, 6"
beneath the water.
Your boat is floating in 200' of water with no land in sight (i.e., you've just
got water with the earth beneath it and water with air, 6" above it).
Looking at the "wheel" from the side and starting at a rotation angle of 090,
as the blade of the wheel rotates clockwise to 180 deg, it is pushing down and
to the left, against a solid non compressible column of water, 200ish feet deep
(it's working as efficiently as it can) and pulling the boat to your right.
Now look at the blades in the opposite quadrant (270 - 360). Starting at 270
and rotating towards 360, the blades are pushing up and to the right, against
........ a 3' 6" column of water with nothing but good old compressible air
above. What happens?
Basically the blades lift that column of water and throw it away into the air,
losing a high percentage of their efficiency to pull down and to the left,
compared to their opposite quadrant.
If you look at 000 - 090, compared to 180 -270, you will see a different set of
comparisons, but I'd bet the net result would still be a greater pull/push to
the right.
Finally, go to a boatyard and look at a power boat on the "hard". Stand in
front of the propellor and pick one blade. Assuming RH, rotate the blade
counter clockwise and as you do, sight 90 deg to the blade pitch and visualize
the direction that the blade will "push" the water. I think you notice that the
blade will be pushing water up, on it's upward swing (into the air), thus
losing efficiency and the net effect will be a pull to the right (your left
standing in front of the prop) .......propwalk.
I don't doubt there are some possible flaws in this description, but it's how I
visualize the overall effect and cause of propwalk.
BTW, propwalk is just as important with twin screw. It's why a twin screw with
inboard turning props handles so much differently as one with outboard turning
props.

Shen

Which way does a boat turn?
 

Yes, I understood where you were going with this. I agree, with the paddle
wheel slightly out of the water, to a little (6'') below, but what about a
sailboat prop, 1' below the water with a boat sitting on top of it. And with
the smaller dia. blade on a S/V there isn't much depth difference between
top and bottom blade. Although even a miniscule difference could account for
prop walk given the RPMs of a small blade?

SV


"Shen44" wrote in message
...
Subject: Which way does a boat turn?
From: "Scott Vernon"

I would guess yes. But I don't know. And I was picturing a side
wheeler.

Sv

Ok, continue to picture a sidewheeler.
Now, in hopes of further clarifying what I'm trying to describe, the
paddlewheel is 6' in diameter and you totally submerge it to a point, say,
6"
beneath the water.
Your boat is floating in 200' of water with no land in sight (i.e., you've
just
got water with the earth beneath it and water with air, 6" above it).
Looking at the "wheel" from the side and starting at a rotation angle of
090,
as the blade of the wheel rotates clockwise to 180 deg, it is pushing down
and
to the left, against a solid non compressible column of water, 200ish feet
deep
(it's working as efficiently as it can) and pulling the boat to your
right.
Now look at the blades in the opposite quadrant (270 - 360). Starting at
270
and rotating towards 360, the blades are pushing up and to the right,
against
....... a 3' 6" column of water with nothing but good old compressible air
above. What happens?
Basically the blades lift that column of water and throw it away into the
air,
losing a high percentage of their efficiency to pull down and to the left,
compared to their opposite quadrant.
If you look at 000 - 090, compared to 180 -270, you will see a different
set of
comparisons, but I'd bet the net result would still be a greater pull/push
to
the right.
Finally, go to a boatyard and look at a power boat on the "hard". Stand in
front of the propellor and pick one blade. Assuming RH, rotate the blade
counter clockwise and as you do, sight 90 deg to the blade pitch and
visualize
the direction that the blade will "push" the water. I think you notice
that the
blade will be pushing water up, on it's upward swing (into the air), thus
losing efficiency and the net effect will be a pull to the right (your
left
standing in front of the prop) .......propwalk.
I don't doubt there are some possible flaws in this description, but it's
how I
visualize the overall effect and cause of propwalk.
BTW, propwalk is just as important with twin screw. It's why a twin screw
with
inboard turning props handles so much differently as one with outboard
turning
props.

Shen

Which way does a boat turn?
 

Yes, I understood where you were going with this. I agree, with the paddle
wheel slightly out of the water, to a little (6'') below, but what about a
sailboat prop, 1' below the water with a boat sitting on top of it. And with
the smaller dia. blade on a S/V there isn't much depth difference between
top and bottom blade. Although even a miniscule difference could account for
prop walk given the RPMs of a small blade?

SV


"Shen44" wrote in message
...
Subject: Which way does a boat turn?
From: "Scott Vernon"

I would guess yes. But I don't know. And I was picturing a side
wheeler.

Sv

Ok, continue to picture a sidewheeler.
Now, in hopes of further clarifying what I'm trying to describe, the
paddlewheel is 6' in diameter and you totally submerge it to a point, say,
6"
beneath the water.
Your boat is floating in 200' of water with no land in sight (i.e., you've
just
got water with the earth beneath it and water with air, 6" above it).
Looking at the "wheel" from the side and starting at a rotation angle of
090,
as the blade of the wheel rotates clockwise to 180 deg, it is pushing down
and
to the left, against a solid non compressible column of water, 200ish feet
deep
(it's working as efficiently as it can) and pulling the boat to your
right.
Now look at the blades in the opposite quadrant (270 - 360). Starting at
270
and rotating towards 360, the blades are pushing up and to the right,
against
....... a 3' 6" column of water with nothing but good old compressible air
above. What happens?
Basically the blades lift that column of water and throw it away into the
air,
losing a high percentage of their efficiency to pull down and to the left,
compared to their opposite quadrant.
If you look at 000 - 090, compared to 180 -270, you will see a different
set of
comparisons, but I'd bet the net result would still be a greater pull/push
to
the right.
Finally, go to a boatyard and look at a power boat on the "hard". Stand in
front of the propellor and pick one blade. Assuming RH, rotate the blade
counter clockwise and as you do, sight 90 deg to the blade pitch and
visualize
the direction that the blade will "push" the water. I think you notice
that the
blade will be pushing water up, on it's upward swing (into the air), thus
losing efficiency and the net effect will be a pull to the right (your
left
standing in front of the prop) .......propwalk.
I don't doubt there are some possible flaws in this description, but it's
how I
visualize the overall effect and cause of propwalk.
BTW, propwalk is just as important with twin screw. It's why a twin screw
with
inboard turning props handles so much differently as one with outboard
turning
props.

Shen

Which way does a boat turn?
 

ct: Which way does a boat turn?
From: "Scott Vernon"

My feeling is that you have to get that prop down really deep (as in submarine)
before this doesn't apply.
As another visual .... next time you back down (and for this purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority of the
disturbed wash you see at the surface will be coming out from underneath the
stbd side of your hull (you may see little or none on the port).
Second, that disturbed wash is getting to the surface ... lifting against air.
It's not the difference in depth between the top and bottom of your blade, it's
the difference in what they "push" against or towards.
The fact that the boat is attop of it doesn't really matter. Many hulls angle
up both astern and to the sides, and the wash, generally doesn't have to go far
before it is free from the hull and can lift into the air (same end results).
Mind you, I have no studies or scientific treatise backing me up on this ....
this is just my own observation and sense of what I'm seeing and why, coupled
with statements from a good number of older wiser boat handlers.

Shen

Yes, I understood where you were going with this. I agree, with the paddle
wheel slightly out of the water, to a little (6'') below, but what about a
sailboat prop, 1' below the water with a boat sitting on top of it. And with
the smaller dia. blade on a S/V there isn't much depth difference between
top and bottom blade. Although even a miniscule difference could account for
prop walk given the RPMs of a small blade?

SV

Which way does a boat turn?
 

ct: Which way does a boat turn?
From: "Scott Vernon"

My feeling is that you have to get that prop down really deep (as in submarine)
before this doesn't apply.
As another visual .... next time you back down (and for this purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority of the
disturbed wash you see at the surface will be coming out from underneath the
stbd side of your hull (you may see little or none on the port).
Second, that disturbed wash is getting to the surface ... lifting against air.
It's not the difference in depth between the top and bottom of your blade, it's
the difference in what they "push" against or towards.
The fact that the boat is attop of it doesn't really matter. Many hulls angle
up both astern and to the sides, and the wash, generally doesn't have to go far
before it is free from the hull and can lift into the air (same end results).
Mind you, I have no studies or scientific treatise backing me up on this ....
this is just my own observation and sense of what I'm seeing and why, coupled
with statements from a good number of older wiser boat handlers.

Shen

Yes, I understood where you were going with this. I agree, with the paddle
wheel slightly out of the water, to a little (6'') below, but what about a
sailboat prop, 1' below the water with a boat sitting on top of it. And with
the smaller dia. blade on a S/V there isn't much depth difference between
top and bottom blade. Although even a miniscule difference could account for
prop walk given the RPMs of a small blade?

SV

Which way does a boat turn?
 

Shen44 wrote:
ct: Which way does a boat turn?
From: "Scott Vernon"


My feeling is that you have to get that prop down really deep (as in submarine)
before this doesn't apply.
As another visual .... next time you back down (and for this purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority of the
disturbed wash you see at the surface will be coming out from underneath the
stbd side of your hull (you may see little or none on the port).

I'm going to slightly disagree here. When you start DIW, the boat (RH
prop) will almost immediately start swinging the stern to port, which in
itself will make the wash come out the stbd.
However, if all things were equal, you should see an equal wash either side.
I frequently use the backing for stopping. When doing this I try to
start a turn to port first, so that once the "walk" kicks in it stops my
swing at about the same time it stops the boat (used to have the final
heading where you want it when stopped) and since I'm watching the wash
so that I know when I'm stopped, it will still, in the majority, be
coming out the stbd side.

otn

Which way does a boat turn?
 

Shen44 wrote:
ct: Which way does a boat turn?
From: "Scott Vernon"


My feeling is that you have to get that prop down really deep (as in submarine)
before this doesn't apply.
As another visual .... next time you back down (and for this purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority of the
disturbed wash you see at the surface will be coming out from underneath the
stbd side of your hull (you may see little or none on the port).

I'm going to slightly disagree here. When you start DIW, the boat (RH
prop) will almost immediately start swinging the stern to port, which in
itself will make the wash come out the stbd.
However, if all things were equal, you should see an equal wash either side.
I frequently use the backing for stopping. When doing this I try to
start a turn to port first, so that once the "walk" kicks in it stops my
swing at about the same time it stops the boat (used to have the final
heading where you want it when stopped) and since I'm watching the wash
so that I know when I'm stopped, it will still, in the majority, be
coming out the stbd side.

otn

Which way does a boat turn?
 

I've watched the responses to this thread and those that came before which
involved the issue of "propwalk" and general boat handling.
To be honest, I've been surprised (though not in Jax's case) how few have
commented on my recent post, either positively or negatively.
However, in retrospect, from past experience I should have known better.
With this in mind, I'm going to try something ....... (power boat handling is
what I am and what I do).
I have over 40 years experience with inboard driven boats (fixed pitch RH,LH,
variable pitch, RH,LH, Z-drive, Cycloidal drive, twin screw (inboard or
outboard turning), triple screw, quad screw) single rudder, twin rudder ....
unbalanced, semi balanced, and balanced rudders, Becker rudders and Schilling
rudders, Kort Nozzles..... so on and so forth.
Now .... I admit to little experience with I/O and outboards ...... BUT......
If you should have a boat handling question regarding powerdriven vessels,
please feel free to E-mail me, and I will be more than happy to try and assist
you.
Please note .... I'm a firm believer that each boat, each condition, each
operator, requires different handling. I make no guarantees that what I might
suggest will work, unless I can board your vessel and work with you(EG and
that will be extremely expensive) .... but, I like trying to solve problems,
and if I can help you with one you have, over the net, that will be great.
So, if you have a question, e-mail me - I'm not going to dump on you - hell I
might thank you for telling me something new.
If you can't get me, try me bud (G he's older than me
in many respects) as I know he will also be willing to help.
G this is a freebie, no strings attached, I just love the subject, no ones
going to drag your ass ..... offer, using E=mail.

Shen

Which way does a boat turn?
 

I've watched the responses to this thread and those that came before which
involved the issue of "propwalk" and general boat handling.
To be honest, I've been surprised (though not in Jax's case) how few have
commented on my recent post, either positively or negatively.
However, in retrospect, from past experience I should have known better.
With this in mind, I'm going to try something ....... (power boat handling is
what I am and what I do).
I have over 40 years experience with inboard driven boats (fixed pitch RH,LH,
variable pitch, RH,LH, Z-drive, Cycloidal drive, twin screw (inboard or
outboard turning), triple screw, quad screw) single rudder, twin rudder ....
unbalanced, semi balanced, and balanced rudders, Becker rudders and Schilling
rudders, Kort Nozzles..... so on and so forth.
Now .... I admit to little experience with I/O and outboards ...... BUT......
If you should have a boat handling question regarding powerdriven vessels,
please feel free to E-mail me, and I will be more than happy to try and assist
you.
Please note .... I'm a firm believer that each boat, each condition, each
operator, requires different handling. I make no guarantees that what I might
suggest will work, unless I can board your vessel and work with you(EG and
that will be extremely expensive) .... but, I like trying to solve problems,
and if I can help you with one you have, over the net, that will be great.
So, if you have a question, e-mail me - I'm not going to dump on you - hell I
might thank you for telling me something new.
If you can't get me, try me bud (G he's older than me
in many respects) as I know he will also be willing to help.
G this is a freebie, no strings attached, I just love the subject, no ones
going to drag your ass ..... offer, using E=mail.

Shen

Which way does a boat turn?
 

ROFLMAO ..... I'll buy into this, but bet neither of us get's one
E-mail on the subject ....... especially from Jax

otn

Shen44 wrote:
I've watched the responses to this thread and those that came before which
involved the issue of "propwalk" and general boat handling.
To be honest, I've been surprised (though not in Jax's case) how few have
commented on my recent post, either positively or negatively.
However, in retrospect, from past experience I should have known better.
With this in mind, I'm going to try something ....... (power boat handling is
what I am and what I do).
I have over 40 years experience with inboard driven boats (fixed pitch RH,LH,
variable pitch, RH,LH, Z-drive, Cycloidal drive, twin screw (inboard or
outboard turning), triple screw, quad screw) single rudder, twin rudder ....
unbalanced, semi balanced, and balanced rudders, Becker rudders and Schilling
rudders, Kort Nozzles..... so on and so forth.
Now .... I admit to little experience with I/O and outboards ...... BUT......
If you should have a boat handling question regarding powerdriven vessels,
please feel free to E-mail me, and I will be more than happy to try and assist
you.
Please note .... I'm a firm believer that each boat, each condition, each
operator, requires different handling. I make no guarantees that what I might
suggest will work, unless I can board your vessel and work with you(EG and
that will be extremely expensive) .... but, I like trying to solve problems,
and if I can help you with one you have, over the net, that will be great.
So, if you have a question, e-mail me - I'm not going to dump on you - hell I
might thank you for telling me something new.
If you can't get me, try me bud (G he's older than me
in many respects) as I know he will also be willing to help.
G this is a freebie, no strings attached, I just love the subject, no ones
going to drag your ass ..... offer, using E=mail.

Shen

Which way does a boat turn?
 

ROFLMAO ..... I'll buy into this, but bet neither of us get's one
E-mail on the subject ....... especially from Jax

otn

Shen44 wrote:
I've watched the responses to this thread and those that came before which
involved the issue of "propwalk" and general boat handling.
To be honest, I've been surprised (though not in Jax's case) how few have
commented on my recent post, either positively or negatively.
However, in retrospect, from past experience I should have known better.
With this in mind, I'm going to try something ....... (power boat handling is
what I am and what I do).
I have over 40 years experience with inboard driven boats (fixed pitch RH,LH,
variable pitch, RH,LH, Z-drive, Cycloidal drive, twin screw (inboard or
outboard turning), triple screw, quad screw) single rudder, twin rudder ....
unbalanced, semi balanced, and balanced rudders, Becker rudders and Schilling
rudders, Kort Nozzles..... so on and so forth.
Now .... I admit to little experience with I/O and outboards ...... BUT......
If you should have a boat handling question regarding powerdriven vessels,
please feel free to E-mail me, and I will be more than happy to try and assist
you.
Please note .... I'm a firm believer that each boat, each condition, each
operator, requires different handling. I make no guarantees that what I might
suggest will work, unless I can board your vessel and work with you(EG and
that will be extremely expensive) .... but, I like trying to solve problems,
and if I can help you with one you have, over the net, that will be great.
So, if you have a question, e-mail me - I'm not going to dump on you - hell I
might thank you for telling me something new.
If you can't get me, try me bud (G he's older than me
in many respects) as I know he will also be willing to help.
G this is a freebie, no strings attached, I just love the subject, no ones
going to drag your ass ..... offer, using E=mail.

Shen

Which way does a boat turn?
 

Shen44 wrote in message
...
ct: Which way does a boat turn?
From: "Scott Vernon"

As another visual .... next time you back down (and for this
purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority
of the
disturbed wash you see at the surface will be coming out from
underneath the
stbd side of your hull (you may see little or none on the
port).

RH prop. Agreed. That say says that (for some reason) the prop is
squirting more water to the right than to the left. In its own
right (sorry!) that will cause the boat's stern to go left. As to
the reason more wash goes to the right . . .

Second, that disturbed wash is getting to the surface ...
lifting against air.
It's not the difference in depth between the top and bottom of
your blade, it's
the difference in what they "push" against or towards.

Once the water has been squirted, what it reacts against (air or
water) doesn't matter in terms of physics, unless it reacts
against a part of the hull

The fact that the boat is attop of it doesn't really matter.
Many hulls angle
up both astern and to the sides, and the wash, generally
doesn't have to go far
before it is free from the hull and can lift into the air (same
end results).

Instead, I'd explain the angle of squirt (lovely scientific term,
don't you think?) you observe as 'the result of hull/skeg
interference'. As the wash spirals away from the prop, the upper
part of the spiral (going left) is interfered with and slowed by
friction with the hull, also often by a skeg supporting the prop
shaft from above. This 'drag' and 'lift' transfers a port pushing
force to the rear of the vessel (reducing the amount of wash
going to port).

The lower part of the spiral is not interfered with so much, and
has freedom to rush off to starboard.

Mind you, I have no studies or scientific treatise backing me
up on this ....
this is just my own observation and sense of what I'm seeing
and why, coupled
with statements from a good number of older wiser boat
handlers.

So we agree on the effect (wash goes to starboard)

We agree that the wash pushing (or not) laterally against
something is what causes the the boat to turn

Your view is that 'pushing against very little' is the agent

My view is that 'pushing against a lot' is the agent

So we can agree that differential push is what causes prop walk

We differ in our explanations of this differential push.You see
different reactions caused between hitting air or water. I see
different reactions caused between hitting boat or water.

In terms of boat handling, this difference between explanations
doesn't matter. It's whatever sticks in a pupil's mind that
matters most. I like 'paddle wheel'. It's easy.

In terms of design (attempting to add or subtract from the
effect) the difference will matter. But only if you want to add
or subtract from the effect!

Shen & JimB - mostly in agreement.

Which way does a boat turn?
 

Shen44 wrote in message
...
ct: Which way does a boat turn?
From: "Scott Vernon"

As another visual .... next time you back down (and for this
purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority
of the
disturbed wash you see at the surface will be coming out from
underneath the
stbd side of your hull (you may see little or none on the
port).

RH prop. Agreed. That say says that (for some reason) the prop is
squirting more water to the right than to the left. In its own
right (sorry!) that will cause the boat's stern to go left. As to
the reason more wash goes to the right . . .

Second, that disturbed wash is getting to the surface ...
lifting against air.
It's not the difference in depth between the top and bottom of
your blade, it's
the difference in what they "push" against or towards.

Once the water has been squirted, what it reacts against (air or
water) doesn't matter in terms of physics, unless it reacts
against a part of the hull

The fact that the boat is attop of it doesn't really matter.
Many hulls angle
up both astern and to the sides, and the wash, generally
doesn't have to go far
before it is free from the hull and can lift into the air (same
end results).

Instead, I'd explain the angle of squirt (lovely scientific term,
don't you think?) you observe as 'the result of hull/skeg
interference'. As the wash spirals away from the prop, the upper
part of the spiral (going left) is interfered with and slowed by
friction with the hull, also often by a skeg supporting the prop
shaft from above. This 'drag' and 'lift' transfers a port pushing
force to the rear of the vessel (reducing the amount of wash
going to port).

The lower part of the spiral is not interfered with so much, and
has freedom to rush off to starboard.

Mind you, I have no studies or scientific treatise backing me
up on this ....
this is just my own observation and sense of what I'm seeing
and why, coupled
with statements from a good number of older wiser boat
handlers.

So we agree on the effect (wash goes to starboard)

We agree that the wash pushing (or not) laterally against
something is what causes the the boat to turn

Your view is that 'pushing against very little' is the agent

My view is that 'pushing against a lot' is the agent

So we can agree that differential push is what causes prop walk

We differ in our explanations of this differential push.You see
different reactions caused between hitting air or water. I see
different reactions caused between hitting boat or water.

In terms of boat handling, this difference between explanations
doesn't matter. It's whatever sticks in a pupil's mind that
matters most. I like 'paddle wheel'. It's easy.

In terms of design (attempting to add or subtract from the
effect) the difference will matter. But only if you want to add
or subtract from the effect!

Shen & JimB - mostly in agreement.

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: "JimB"

Shen44 wrote:
As another visual .... next time you back down (and for this
purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority
of the
disturbed wash you see at the surface will be coming out from
underneath the
stbd side of your hull (you may see little or none on the
port).

RH prop. Agreed. That say says that (for some reason) the prop is
squirting more water to the right than to the left. In its own
right (sorry!) that will cause the boat's stern to go left. As to
the reason more wash goes to the right .

I don't think it's "squirting" more water to the right as much as it's showing
more cavitation (not sure I'm using that word correctly) due to the fact the
blade is pushing the water up (into the air) and away.


Second, that disturbed wash is getting to the surface ...
lifting against air.
It's not the difference in depth between the top and bottom of
your blade, it's
the difference in what they "push" against or towards.

Once the water has been squirted, what it reacts against (air or
water) doesn't matter in terms of physics, unless it reacts
against a part of the hull

Here, I'd liken it to pushing against a door that's latched, with your right
hand, while at the same time pushing against a door that isn't latched, with
your left hand.


The fact that the boat is attop of it doesn't really matter.
Many hulls angle
up both astern and to the sides, and the wash, generally
doesn't have to go far
before it is free from the hull and can lift into the air (same
end results).

Instead, I'd explain the angle of squirt (lovely scientific term,
don't you think?) you observe as 'the result of hull/skeg
interference'. As the wash spirals away from the prop, the upper
part of the spiral (going left) is interfered with and slowed by
friction with the hull, also often by a skeg supporting the prop
shaft from above. This 'drag' and 'lift' transfers a port pushing
force to the rear of the vessel (reducing the amount of wash
going to port).

The lower part of the spiral is not interfered with so much, and
has freedom to rush off to starboard.

Understood, but I'm inclined to consider this a secondary cause and effect, not
the primary.G

Shen



Mind you, I have no studies or scientific treatise backing me
up on this ....
this is just my own observation and sense of what I'm seeing
and why, coupled
with statements from a good number of older wiser boat
handlers.

So we agree on the effect (wash goes to starboard)

We agree that the wash pushing (or not) laterally against
something is what causes the the boat to turn

Your view is that 'pushing against very little' is the agent

My view is that 'pushing against a lot' is the agent

So we can agree that differential push is what causes prop walk

We differ in our explanations of this differential push.You see
different reactions caused between hitting air or water. I see
different reactions caused between hitting boat or water.

In terms of boat handling, this difference between explanations
doesn't matter. It's whatever sticks in a pupil's mind that
matters most. I like 'paddle wheel'. It's easy.

In terms of design (attempting to add or subtract from the
effect) the difference will matter. But only if you want to add
or subtract from the effect!

Shen & JimB - mostly in agreement.

Which way does a boat turn?
 

Subject: Which way does a boat turn?
From: "JimB"

Shen44 wrote:
As another visual .... next time you back down (and for this
purpose start DIW)
and start going astern look at your prop wash.
You should notice two things about it.
First, on a high percentage of single screw boats, the majority
of the
disturbed wash you see at the surface will be coming out from
underneath the
stbd side of your hull (you may see little or none on the
port).

RH prop. Agreed. That say says that (for some reason) the prop is
squirting more water to the right than to the left. In its own
right (sorry!) that will cause the boat's stern to go left. As to
the reason more wash goes to the right .

I don't think it's "squirting" more water to the right as much as it's showing
more cavitation (not sure I'm using that word correctly) due to the fact the
blade is pushing the water up (into the air) and away.


Second, that disturbed wash is getting to the surface ...
lifting against air.
It's not the difference in depth between the top and bottom of
your blade, it's
the difference in what they "push" against or towards.

Once the water has been squirted, what it reacts against (air or
water) doesn't matter in terms of physics, unless it reacts
against a part of the hull

Here, I'd liken it to pushing against a door that's latched, with your right
hand, while at the same time pushing against a door that isn't latched, with
your left hand.


The fact that the boat is attop of it doesn't really matter.
Many hulls angle
up both astern and to the sides, and the wash, generally
doesn't have to go far
before it is free from the hull and can lift into the air (same
end results).

Instead, I'd explain the angle of squirt (lovely scientific term,
don't you think?) you observe as 'the result of hull/skeg
interference'. As the wash spirals away from the prop, the upper
part of the spiral (going left) is interfered with and slowed by
friction with the hull, also often by a skeg supporting the prop
shaft from above. This 'drag' and 'lift' transfers a port pushing
force to the rear of the vessel (reducing the amount of wash
going to port).

The lower part of the spiral is not interfered with so much, and
has freedom to rush off to starboard.

Understood, but I'm inclined to consider this a secondary cause and effect, not
the primary.G

Shen



Mind you, I have no studies or scientific treatise backing me
up on this ....
this is just my own observation and sense of what I'm seeing
and why, coupled
with statements from a good number of older wiser boat
handlers.

So we agree on the effect (wash goes to starboard)

We agree that the wash pushing (or not) laterally against
something is what causes the the boat to turn

Your view is that 'pushing against very little' is the agent

My view is that 'pushing against a lot' is the agent

So we can agree that differential push is what causes prop walk

We differ in our explanations of this differential push.You see
different reactions caused between hitting air or water. I see
different reactions caused between hitting boat or water.

In terms of boat handling, this difference between explanations
doesn't matter. It's whatever sticks in a pupil's mind that
matters most. I like 'paddle wheel'. It's easy.

In terms of design (attempting to add or subtract from the
effect) the difference will matter. But only if you want to add
or subtract from the effect!

Shen & JimB - mostly in agreement.