Thrust vectoring
 

bject: Thrust vectoring
From: (JAXAshby)
Date: 03/26/2004 13:53 Pacific Standard Time
Message-id:

Single screw .... With full left rudder, kick ahead, bow will swing to
port .... due mainly to rudder and some prop walk (right hand prop).
With rudder hard left, kick astern, stern will swing to port .... all
prop walk, has nothing to due with rudder placement(rudder could be hard
left or hard right, initial affect will be the same).

true

HOLY EIGHT SMOKES !!!!!! Jax agrees with otn on something !!!!!
Hey OTN .... are you sure you meant to say that?
Hey Jax .... I bet you picked up on the difference between inboard turning and
outboard turning props, too .... you wanna esplain that?

Shen

Thrust vectoring
 

JAXAshby wrote in message
...
jim, asym thrust has been a known factor since before WW2.

Since Pontius was a pilot, Jax. So you got the idea from
aviation.

What I was querying (though I didn't make that very clear) was
your application of the theory to boat prop walk, where the boat
velocities are trivial, the lateral dimensions of the prop are
trivial, and the inertia of the vessel is large. Your argument
was a bit like talking about the effect on boat pitch due to yaw
through the gyroscopic effect of a running engine. It's there.
But it's trivial.

I was also querying your other theories of the causes of prop
walk, which I certainly don't understand.

JimB

Interesting theory. Can't think where you got that from.
Better check the trig though. 1 ft/sec astern, typical prop
tip speed about 50ft/sec, lets say one 1 degree.
Differential effect of 20deg shaft angle, 1-cos20 = 0.06deg.
Lets say 1/20 degree. Compared to a typical prop pitch of
20deg or so that means that 1/400 of your thrust (800 lb?
reduced to 2lb) is being exercised over a moment arm of 16
inches to turn your vessel.

OK, that's coarse maths from the back of an envelope, with a
margin of error of maybe an order. But I still don't think
that even 30 ft/lb is going to turn your vessel. That's
what
I use to tighten my nuts. And it reduces to zero when you
have zero stern way.

So your theory can only true when the boat is actually
travelling in reverse (your definition of backing up?).
It is utterly trivial compared to the paddle wheel effect.
You can test this statement by selecting reverse while
moving slowly forward. The vessel won't kick first
one way, then the other. It'll go the paddle wheel way.

It is also caused to some extent by the contrainment of
the prop wash against
the hull on the up side blade, compared to no
constrainment on the down side
blade.

Don't understand that.

All forces are the result of changes in momentum. The wash
spirals away from the prop. Read on.

On the upper side, the lateral speed of the spiral is slowed
by friction against the ship's hull. The lower side much
less so. So the lower lateral momentum added is greater
than the upper.

The result is a force as if paddled by the lower blades.

You could also think of it as the frictional force exerted
on the hull by slowing the lateral speed of the upper part
of the spiral.

Whichever, it's the opposite direction to your theory,
which, in turn, doesn't tie in with my experience.

JimB

Thrust vectoring
 

otnmbrd wrote in message
k.net...
Single screw .... With full left rudder, kick ahead, bow will
swing to
port .... due mainly to rudder and some prop walk (right hand
prop).
With rudder hard left, kick astern, stern will swing to port
..... all
prop walk, has nothing to due with rudder placement(rudder
could be hard
left or hard right, initial affect will be the same).
The only way to shield a prop from prop walk, that I know of is
a Kort
Nozzle or similar shield.

There's very little prop walk on traditional wood trawlers, when
the prop is set almost half way down a 3m deep keel in a cutaway.

Also, many Greek fishing vessels (enormously over-engined with
old bus engines 300hp driving a 30ft caique) to put long skegs in
front of the prop and big lateral plates extending sideways at
water level to stop air being drawn into these mammoth blades.
This also keeps nets and ropes clear, and seems to minimise prop
walk.

I don't know a Kort nozzle, but if it's a protective cylinder
around the prop with a skeg and cross shaped blades supporting it
in front, that's what I meant by 'shield'. Some old, single
engined tugs used to use these and I suspect the Greek approach
is a half way house.

Also on hydrofoils, where the prop is 2m deep with no hull
interference in sight. But that's a bit exotic, since most
hydrofoils are twin screw.

JimB

Thrust vectoring
 

schlackoff, congratulations on your flip-flop. from instant one I have been
saying the boat MUST be moving for the rudder to be effective in reverse, while
you kept saying No the prop pulls enough water forward to make it work.

at least I am glad you saw the light. interesting how you changed position and
claimed it as your own all along.

t can
also be applied to moving ahead,

no, it can not. water *pushed* over a rudder can cause a rudder to turn a
boat, while water "pulled" over a rudder can not.


Jax, quit worrying about push and pull.
Take a sailboat and start backing it with the engine.... get up the right
amount of speed and shut down the engine. You can now steer that boat because
of the forces of the water PASSING over that rudder, exert a steering force.
Hoist sails and trim them to start getting headway (you are not pushing water
over the rudder you are passing water over the rudder) and once you have
sufficient speed, this water passing over the rudder will exert a force to
steer the vessel.... hence it applies astern or ahead.
Too simple for you to understand? ...... oh well......

Shen

Thrust vectoring
 

schlackoff, English is beyond you.

Single screw .... With full left rudder, kick ahead, bow will swing to
port .... due mainly to rudder and some prop walk (right hand prop).
With rudder hard left, kick astern, stern will swing to port .... all
prop walk, has nothing to due with rudder placement(rudder could be hard
left or hard right, initial affect will be the same).

true

HOLY EIGHT SMOKES !!!!!! Jax agrees with otn on something !!!!!
Hey OTN .... are you sure you meant to say that?
Hey Jax .... I bet you picked up on the difference between inboard turning
and
outboard turning props, too .... you wanna esplain that?

Shen

Thrust vectoring
 

That implies no net lateral force.


that is correct.

Thrust vectoring
 

There's very little prop walk on traditional wood trawlers, when
the prop is set almost half way down a 3m deep keel

That's because there is almost no "end-plate" effect from the hull.

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)


ROFL (see my other post on steering)
You obviously don't know what I said, and I can guarantee you can't find a post
of mine which backs up your statement below (unless you take something out of
context)
Sorry Jax, as per usual, you are wrong .... I didn't flip-flop and never said
what you are crediting me with.

Shen


schlackoff, congratulations on your flip-flop. from instant one I have been
saying the boat MUST be moving for the rudder to be effective in reverse,
while
you kept saying No the prop pulls enough water forward to make it work.

at least I am glad you saw the light. interesting how you changed position
and
claimed it as your own all along.

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)


So you can't explain the difference .... thought not.

Shen

schlackoff, English is beyond you.

Hey Jax .... I bet you picked up on the difference between inboard turning
and
outboard turning props, too .... you wanna esplain that?

Shen

Thrust vectoring
 

Subject: Thrust vectoring
From: "JimB"
Date: 03/27/2004 04:21 Pacific Standard Time
Message-id: Sre9c.1164$aQ3.634@newsfe1-win


otnmbrd wrote in message
nk.net...
Single screw .... With full left rudder, kick ahead, bow will
swing to
port .... due mainly to rudder and some prop walk (right hand
prop).
With rudder hard left, kick astern, stern will swing to port
.... all
prop walk, has nothing to due with rudder placement(rudder
could be hard
left or hard right, initial affect will be the same).
The only way to shield a prop from prop walk, that I know of is
a Kort
Nozzle or similar shield.

There's very little prop walk on traditional wood trawlers, when
the prop is set almost half way down a 3m deep keel in a cutaway.

Please explain what you mean by "trawler" (fishing or yacht) and "cutaway" and
what the depth of the prop has to do with it.


Also, many Greek fishing vessels (enormously over-engined with
old bus engines 300hp driving a 30ft caique) to put long skegs in
front of the prop and big lateral plates extending sideways at
water level to stop air being drawn into these mammoth blades.
This also keeps nets and ropes clear, and seems to minimise prop
walk.

Interesting.


I don't know a Kort nozzle, but if it's a protective cylinder
around the prop with a skeg and cross shaped blades supporting it
in front, that's what I meant by 'shield'. Some old, single
engined tugs used to use these and I suspect the Greek approach
is a half way house.

I can see where this stuff together would cut down propwalk. A Kort nozzle can
be found on fishing boats, but your main application will be tugs. It's a
shaped cylinder, generally attached to the hull, which surrounds the prop,
entirely.
It's main function is to increase "bollard pull", but because it surrounds the
prop, the prop can not "pull" to one side (propwalk) since all thrust is
directed out the nozzle, either ahead or astern.

Also on hydrofoils, where the prop is 2m deep with no hull
interference in sight. But that's a bit exotic, since most
hydrofoils are twin screw.

JimB

Not sure why this reference to depth of a prop in relation to a hull. I may be
reading you wrong, but, for instance, take a single screw ship where the prop
is generally set fairly deep on the hull..... they tend to torque to a
fairtheewell.

Shen

Thrust vectoring
 

schlackoff, nice flip-flop.

ROFL (see my other post on steering)
You obviously don't know what I said, and I can guarantee you can't find a
post
of mine which backs up your statement below (unless you take something out of
context)
Sorry Jax, as per usual, you are wrong .... I didn't flip-flop and never said
what you are crediting me with.

Shen


schlackoff, congratulations on your flip-flop. from instant one I have been
saying the boat MUST be moving for the rudder to be effective in reverse,
while
you kept saying No the prop pulls enough water forward to make it work.

at least I am glad you saw the light. interesting how you changed position
and
claimed it as your own all along.

Thrust vectoring
 

what the depth of the prop has to do with it.

Not sure why this reference to depth of a prop in relation to a hull.

Shen

schlackoff, can you say "end plate effect"?

Thrust vectoring
 

ubject: Thrust vectoring
From: (JAXAshby)
Date: 03/27/2004 15:53 Pacific Standard Time
Message-id:

what the depth of the prop has to do with it.

Not sure why this reference to depth of a prop in relation to a hull.

Shen

schlackoff, can you say "end plate effect"?


Yup, "end plate effect" ...don't mean squat to me.
Now, take a ship in ballast (prop tips at the water surface) put it astern ....
sumbitch will torque to port (RT hand prop) to a fairtheewell.
Take the same ship and load it (prop tips now 30 underwater) put it astern ....
sumbitch will torque to port to a fairtheewell..... some cases more, some cases
less ...gots ta watch them some cases.
This what yer talkin about?

Shen

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/27/2004 17:49 Pacific Standard Time
Message-id:

schlackoff postutlates:

Yup, "end plate effect" ...don't mean squat to me.



.....and you can't comment on what I wrote and whether it relates to the
subject.
Hey, Dotsan, read Jaxass's responses. Do you really think they have anything to
do with "going astern" and steering and in any way enlighten you on the
subject?
Jax writes garbage based on what he's read and heard, not on what he knows from
practical experience ..... HE HAS NONE !!!

Shen

Thrust vectoring
 

Jax writes garbage based on what he's read and heard, not on what he knows
from
practical experience ..... HE HAS NONE !!!

Shen

schlackoff, I have understood this simple stuff for more than forty years. You
don't understand it even to this day.

Let me help you out here. a rudder has NO effect on which way a boat is going
in reserve because of the prop. None. Nada. Zip. Zero. Nothing.

That's a fact of physics, schlackoff. get used to it.

Thrust vectoring
 

schlackoff postutlates:

Yup, "end plate effect" ...don't mean squat to me.

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/27/2004 18:23 Pacific Standard Time
Message-id:

Jax writes garbage based on what he's read and heard, not on what he knows
from
practical experience ..... HE HAS NONE !!!

Shen

schlackoff, I have understood this simple stuff for more than forty years.
You
don't understand it even to this day.

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve because of the prop. None. Nada. Zip. Zero. Nothing.

That's a fact of physics, schlackoff. get used to it.


Jaxoff, get used to it.... it's one thing to be able to quote a bunch of stuff
you read in a book and say you know what it means. It's another thing, entirely
to be able to apply that information to practical use.
It it more evident with every post you make, that you can quote crap you've
read, all day, but don't have a clue as to what it means or how to use it in a
practical sense.

I've had my fun with you on another one of your stupid attempts at showing us
what you know, and as per usual, you've failed miserably .....see ya.....

Shen

Thrust vectoring
 

Aww now, come on Shen. Why not ask the dummy to ride with you for a
week for some real world experience .... just be sure he signs the
release form ... dipsquat will probably fall on his ass, the first time
he goes through a watertight door.

Shen44 wrote:
Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/27/2004 18:23 Pacific Standard Time
Message-id:

Jax writes garbage based on what he's read and heard, not on what he knows
from
practical experience ..... HE HAS NONE !!!

Shen

schlackoff, I have understood this simple stuff for more than forty years.
You
don't understand it even to this day.

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve because of the prop. None. Nada. Zip. Zero. Nothing.

That's a fact of physics, schlackoff. get used to it.



Jaxoff, get used to it.... it's one thing to be able to quote a bunch of stuff
you read in a book and say you know what it means. It's another thing, entirely
to be able to apply that information to practical use.
It it more evident with every post you make, that you can quote crap you've
read, all day, but don't have a clue as to what it means or how to use it in a
practical sense.

I've had my fun with you on another one of your stupid attempts at showing us
what you know, and as per usual, you've failed miserably .....see ya.....

Shen

Thrust vectoring
 

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve because of the prop. None. Nada. Zip. Zero. Nothing.

That's a fact of physics, schlackoff. get used to it.

Your premise is wrong.

As the vessel goes in reverse, water presses against the face of the rudder if
it is turned to port or starboard. The greater the speed, the more the water
force on the rudder. At sufficient speed, the force of the water against the
rudder overcomes the prop walk and the boat will follow the rudder, not the
prop.

When speed is reduced, the vessel will reach a point where the prop walk force
is greater than the rudder force and the rudder will not be useful to steering.

It could be argued that at sternway at all, there is some effect from the
rudder. It may not be enough to overcome the prop walk at the slowest speeds,
but in principle the prop walk is finitely reduced
with even the slightest pressure against an opposing rudder.

The water hitting the rudder is not being pulled over the rudder by the prop,
any more than the bow wake is created by water being pulled against the bow
when going forward. I think everybody agrees on that. But to say a rudder as NO
effect on a boat going in reverse because of prop walk is not correct. The
rudder exerts increasing influence as speed increases.

This may not be true for boats with itsy bitsy rudders, btw. It might not be
possible to get enough water pressure on an 8 1/2 X 11" rudder to offset prop
walk. :-)

Thrust vectoring
 

go ahead, schlackoff. try to back up a boat using the prop and rudder. do it
around expensive boats, and cops too if you can. Have a beer or two first,
'cuz it is so easy.

schlackoff, yesterday you flip-flopped rather nicely. today, you are back to
saying what you originally said. i.e. that you are a dummy.

Jax writes garbage based on what he's read and heard, not on what he knows
from
practical experience ..... HE HAS NONE !!!

Shen

schlackoff, I have understood this simple stuff for more than forty years.
You
don't understand it even to this day.

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve because of the prop. None. Nada. Zip. Zero. Nothing.

That's a fact of physics, schlackoff. get used to it.


Jaxoff, get used to it.... it's one thing to be able to quote a bunch of
stuff
you read in a book and say you know what it means. It's another thing,
entirely
to be able to apply that information to practical use.
It it more evident with every post you make, that you can quote crap you've
read, all day, but don't have a clue as to what it means or how to use it in
a
practical sense.

I've had my fun with you on another one of your stupid attempts at showing us
what you know, and as per usual, you've failed miserably .....see ya.....

Shen

Thrust vectoring
 

on an Irwin 37? what watertight door?

Aww now, come on Shen. Why not ask the dummy to ride with you for a
week for some real world experience .... just be sure he signs the
release form ... dipsquat will probably fall on his ass, the first time
he goes through a watertight door.

Shen44 wrote:
Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/27/2004 18:23 Pacific Standard Time
Message-id:

Jax writes garbage based on what he's read and heard, not on what he knows
from
practical experience ..... HE HAS NONE !!!

Shen

schlackoff, I have understood this simple stuff for more than forty years.
You
don't understand it even to this day.

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve because of the prop. None. Nada. Zip. Zero. Nothing.

That's a fact of physics, schlackoff. get used to it.



Jaxoff, get used to it.... it's one thing to be able to quote a bunch of
stuff
you read in a book and say you know what it means. It's another thing,
entirely
to be able to apply that information to practical use.
It it more evident with every post you make, that you can quote crap you've
read, all day, but don't have a clue as to what it means or how to use it
in a
practical sense.

I've had my fun with you on another one of your stupid attempts at showing
us
what you know, and as per usual, you've failed miserably .....see ya.....

Shen

Thrust vectoring
 

gould, you are right *IF* the boat is moving. However, not right if the boat
is not moving. That's a fact of physics. What's more I explained in easy
terms why. What's more I gave unimpeachable references to backup what I
explained. In addition, I gave the name of a famous physicist to google to
your hearts content, as this particular physicist actually made a movie of the
effect because so many people could not believe something they did not
understand intuitively.

the prop has zero effect on the rudder when in reverse. zip. nada. squat.
nothing.

it can't.

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve because of the prop. None. Nada. Zip. Zero. Nothing.

That's a fact of physics, schlackoff. get used to it.

Your premise is wrong.

As the vessel goes in reverse, water presses against the face of the rudder
if
it is turned to port or starboard. The greater the speed, the more the water
force on the rudder. At sufficient speed, the force of the water against the
rudder overcomes the prop walk and the boat will follow the rudder, not the
prop.

When speed is reduced, the vessel will reach a point where the prop walk
force
is greater than the rudder force and the rudder will not be useful to
steering.

It could be argued that at sternway at all, there is some effect from the
rudder. It may not be enough to overcome the prop walk at the slowest speeds,
but in principle the prop walk is finitely reduced
with even the slightest pressure against an opposing rudder.

The water hitting the rudder is not being pulled over the rudder by the prop,
any more than the bow wake is created by water being pulled against the bow
when going forward. I think everybody agrees on that. But to say a rudder as
NO
effect on a boat going in reverse because of prop walk is not correct. The
rudder exerts increasing influence as speed increases.

This may not be true for boats with itsy bitsy rudders, btw. It might not be
possible to get enough water pressure on an 8 1/2 X 11" rudder to offset prop
walk. :-)

Thrust vectoring
 

JAXAshby wrote in message
...
There's very little prop walk on traditional wood trawlers,
when
the prop is set almost half way down a 3m deep keel

That's because there is almost no "end-plate" effect from the
hull.

Correct. I was just pointing out some other low prop walk cases.

JimB

Thrust vectoring
 

Shen44 wrote in message
...
Subject: Thrust vectoring

There's very little prop walk on traditional wood trawlers,
when
the prop is set almost half way down a 3m deep keel in a
cutaway.

Please explain what you mean by "trawler" (fishing or yacht)
and "cutaway" and
what the depth of the prop has to do with it.

To be exact, a Brixham Trawler, a 75ft gaff rigged ketch,
designed with a powerful rig for sail trawling. The keel is
straight from stem to stern, about 1m draft at the stem, 3m draft
at the stern. The rudder is mounted 20degrees off vertical. The
aft hull is flat, wide beamed, and lifts above waterline at the
rudder post. The prop is mounted 1.5m deep, in a 60cm (2ft!) arc
cut into the keel just forward of the rudder hinge. The effect is
that the reverse wash of the prop runs down each side of a
vertically straight keel - which I assume kills the spiralling of
the prop wash on both sides equally. Whereas most modern vessels
have the upper part of their prop wash losing energy to the hull
bottom through friction, and no other interference.

I don't know a Kort nozzle, but if it's a protective cylinder
around the prop with a skeg and cross shaped blades supporting
it
in front, that's what I meant by 'shield'. Some old, single
engined tugs used to use these and I suspect the Greek
approach
is a half way house.

I can see where this stuff together would cut down propwalk. A
Kort nozzle can
be found on fishing boats, but your main application will be
tugs. It's a
shaped cylinder, generally attached to the hull, which
surrounds the prop,
entirely.
It's main function is to increase "bollard pull", but because
it surrounds the
prop, the prop can not "pull" to one side (propwalk) since all
thrust is
directed out the nozzle, either ahead or astern.

I think the key factor here is the cruciform blades supporting
the cylinder in front of the prop, which act as flow
straighteners. No spiral flow along the hull = no prop walk.

Also on hydrofoils, where the prop is 2m deep with no hull
interference in sight. But that's a bit exotic, since most
hydrofoils are twin screw.

Not sure why this reference to depth of a prop in relation to a
hull. I may be
reading you wrong, but, for instance, take a single screw ship
where the prop
is generally set fairly deep on the hull..... they tend to
torque to a
fairtheewell.

If the prop's deep, but close to a horizontal surface (the hull)
you'll get good prop walk. Because the hull, through friction,
kills the lateral velocity of the spiralling wash on top, but the
lower spiral rushes off, giving you asymmetric reverse thrust.
Paddle wheel effect if you like. If the prop is well clear of the
hull, just look at the shaft supports to design prop walk out. If
you've got a vertical blade supporting the shaft, stick a
balancing skeg below it. Keeps the ropes clear too.

JimB

Thrust vectoring
 

gould, you are right *IF* the boat is moving. However, not right if the boat
is not moving.

We agree.

I took issue with your statement:

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve because of the prop.

because the phrase "which way a boat is going in reserve (sic)" implies the
boat is in motion. Rather obviously, if the boat is going somewhere, it must be
in motion.

Putting the boat in reverse will (after a split second) result in sternway
unless the engine is not running
or the vessel is lashed to the dock. When the sternway becomes sufficient, the
rudder exerts greater influence on the direction of boat than the prop walk
does.
In my experience. Unlike some here I don't have a string of degrees and
abbreviations following my name, (unless S.O.B. counts), so I can't argue the
applicable theories of physics or fluid dynamics....... but by the same token I
don't have to conduct an "experiment" to know how a single screw with a fair
size rudder behaves in reverse. :-)

Thrust vectoring
 

gould, you are right *IF* the boat is moving. However, not right if the
boat
is not moving.

We agree.

I took issue with your statement:

Let me help you out here. a rudder has NO effect on which way a boat is
going
in reserve ******* because of the prop*********.

sorry, the sentence structure may not have been clear. I was saying the prop
caused no change in boat direction because of the rudder. The prop and rudder
are net zero between them

yup, the prop can make the boat move and then the rudder can steer the boat.
but the prop wash in reverse does nothing to the rudder, as opposed to prop
wash in forward which does.

sorry about my sentence structure not being clear as to what I was trying to
say.



because the phrase "which way a boat is going in reserve (sic)" implies the
boat is in motion. Rather obviously, if the boat is going somewhere, it must
be
in motion.

Putting the boat in reverse will (after a split second) result in sternway
unless the engine is not running
or the vessel is lashed to the dock. When the sternway becomes sufficient,
the
rudder exerts greater influence on the direction of boat than the prop walk
does.
In my experience. Unlike some here I don't have a string of degrees and
abbreviations following my name, (unless S.O.B. counts), so I can't argue the
applicable theories of physics or fluid dynamics....... but by the same token
I
don't have to conduct an "experiment" to know how a single screw with a fair
size rudder behaves in reverse. :-)

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)

What Irwin 37? If you think I own one, you're thinking of the wrong guy .....
sides, I'm thinking of a "motorsailer" so I can enjoy the pleasures of both
worlds.

Shen

on an Irwin 37? what watertight door?

Aww now, come on Shen. Why not ask the dummy to ride with you for a
week for some real world experience .... just be sure he signs the
release form ... dipsquat will probably fall on his ass, the first time
he goes through a watertight door.

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/28/2004 05:18 Pacific Standard Time
Message-id:

go ahead, schlackoff. try to back up a boat using the prop and rudder. do
it
around expensive boats, and cops too if you can. Have a beer or two first,
'cuz it is so easy.

It is, if you know how to do it and can make use of the various factors
involved, and/or compensate between their effects.

schlackoff, yesterday you flip-flopped rather nicely. today, you are back to
saying what you originally said. i.e. that you are a dummy.

It would appear that you don't have a clue WHAT I said, much less understand
the meaning.

Shen

Thrust vectoring
 

"motorsailor", eh? that's a hermaphordite that nobody on either side of the
bed wants to play with. a twig too small to be a stick, and too long to be a
clit.






What Irwin 37? If you think I own one, you're thinking of the wrong guy .....
sides, I'm thinking of a "motorsailer" so I can enjoy the pleasures of both
worlds.

Shen

on an Irwin 37? what watertight door?

Aww now, come on Shen. Why not ask the dummy to ride with you for a
week for some real world experience .... just be sure he signs the
release form ... dipsquat will probably fall on his ass, the first time
he goes through a watertight door.

Thrust vectoring
 

there you have if, folks. schlackoff declares himself a greater physicist than
Feynman. Wait until the Nobel Committee learns fo schlackoff. Fame and
fortune will soon be his.

go ahead, schlackoff. try to back up a boat using the prop and rudder. do
it
around expensive boats, and cops too if you can. Have a beer or two first,
'cuz it is so easy.

It is, if you know how to do it and can make use of the various factors
involved, and/or compensate between their effects.

schlackoff, yesterday you flip-flopped rather nicely. today, you are back
to
saying what you originally said. i.e. that you are a dummy.

It would appear that you don't have a clue WHAT I said, much less understand
the meaning.

Shen

Thrust vectoring
 

Subject: Thrust vectoring
From: "JimB"

Shen44 wrote in message

Subject: Thrust vectoring

There's very little prop walk on traditional wood trawlers,
when
the prop is set almost half way down a 3m deep keel in a
cutaway.

Please explain what you mean by "trawler" (fishing or yacht)
and "cutaway" and
what the depth of the prop has to do with it.

To be exact, a Brixham Trawler, a 75ft gaff rigged ketch,
designed with a powerful rig for sail trawling. The keel is
straight from stem to stern, about 1m draft at the stem, 3m draft
at the stern. The rudder is mounted 20degrees off vertical. The
aft hull is flat, wide beamed, and lifts above waterline at the
rudder post. The prop is mounted 1.5m deep, in a 60cm (2ft!) arc
cut into the keel just forward of the rudder hinge. The effect is
that the reverse wash of the prop runs down each side of a
vertically straight keel - which I assume kills the spiralling of
the prop wash on both sides equally.

OK, think I see what you're saying.
First off, I used to run a 65 foot boat with a similar configuration and
remember a beautiful old 45' ketch with the same thing ... both had large
degrees of "propwalk".
Secondly, I think we may have different views of what is the major cause of
prop walk (I attribute it to the pitch of the blades pulling to a greater
degree on the "down stroke" side of the revolution, than the "upstroke side").

Whereas most modern vessels
have the upper part of their prop wash losing energy to the hull
bottom through friction, and no other interference.

I think we're on the same track but drawing different conclusions.


I can see where this stuff together would cut down propwalk. A
Kort nozzle can
be found on fishing boats, but your main application will be
tugs. It's a
shaped cylinder, generally attached to the hull, which
surrounds the prop,
entirely.
It's main function is to increase "bollard pull", but because
it surrounds the
prop, the prop can not "pull" to one side (propwalk) since all
thrust is
directed out the nozzle, either ahead or astern.

I think the key factor here is the cruciform blades supporting
the cylinder in front of the prop, which act as flow
straighteners. No spiral flow along the hull = no prop walk.

In the case of a Kort nozzle, there are no cruciform blades supporting the
nozzle in front of the prop. The nozzle is "hung" beneath the hull and left as
clear as possible in front to aid a clear flow to the prop (kinda like the
nacelle surrounding a jet engine).


If the prop's deep, but close to a horizontal surface (the hull)
you'll get good prop walk. Because the hull, through friction,
kills the lateral velocity of the spiralling wash on top, but the
lower spiral rushes off, giving you asymmetric reverse thrust.

Here I have to disagree that the prop has to be close to the hull when deep to
get a good degree of walk .... take for instance any twin screw vessel where
the props are away ... you still get good prop walk (Before some one says this
is due to off center thrust .... shift to inboard turning wheels and you'll see
a marked difference).

Paddle wheel effect if you like. If the prop is well clear of the
hull, just look at the shaft supports to design prop walk out. If
you've got a vertical blade supporting the shaft, stick a
balancing skeg below it. Keeps the ropes clear too.

BG Why would I want to design "propwalk" out? "Propwalk" is my friend!

Shen

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)

One thing I've learned from reading Jaxcrap ....his opinion is basically
useless and based solely on what he's read and misinterpreted.


"motorsailor", eh? that's a hermaphordite that nobody on either side of the
bed wants to play with. a twig too small to be a stick, and too long to be a
clit.

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/28/2004 09:31 Pacific Standard Time
Message-id:

there you have if, folks. schlackoff declares himself a greater physicist
than
Feynman. Wait until the Nobel Committee learns fo schlackoff. Fame and
fortune will soon be his.


G Never hoid of this Feynman character, before this thread, but if he, like
you cannot back a boat up and steer it using prop and rudder, then that's a
boat handling problem first, a physics problem second.
Hey, for $500/hr (you supply the boat) I'll gladly try and teach you, although
I've noticed you have a serious problem translating what you read into
practical use, so it may get expensive and I doubt you'll ever be any good at
it.G

Shen

Thrust vectoring
 

I attribute it to the pitch of the blades pulling to a greater
degree on the "down stroke" side of the revolution, than the "upstroke side"

This is only true -- for a fixed blade prop -- when the shaft is angled AND the
boat is moving.

Thrust vectoring
 

Never hoid of this Feynman character ...

here you go. 467,000 hits for you read. next time you will know who this
famous man was.

http://www.google.com/search?hl=en&i...59-1&q=feynman

btw schlackoff, Feynman won his Nobel prize in physics long ago, which he got
his before you'll get yours.

... before this thread, but if he, like
you cannot back a boat up and steer it using prop and rudder, then that's a
boat handling problem first, a physics problem second.
Hey, for $500/hr (you supply the boat) I'll gladly try and teach you,
although
I've noticed you have a serious problem translating what you read into
practical use, so it may get expensive and I doubt you'll ever be any good at
it.G

Shen

Thrust vectoring
 

you are right about one thing, schlackoff. I don't have any personal experience
with hermaphordites. you have me beat on that score.


One thing I've learned from reading Jaxcrap ....his opinion is basically
useless and based solely on what he's read and misinterpreted.


"motorsailor", eh? that's a hermaphordite that nobody on either side of the
bed wants to play with. a twig too small to be a stick, and too long to be
a
clit.

Thrust vectoring
 

schlackoff, three day ago you said a prop in reverse would affect a rudder,
then you read my explanation of the phenomenon and flip-flopped. Now, you have
forgotten what your read, or remember what you understood then, and have
flip-flopped back.

tell us again how you are going to win the Nobel prize in physics as you prove
Feynman wrong.

Shen44 wrote in message

Subject: Thrust vectoring

There's very little prop walk on traditional wood trawlers,
when
the prop is set almost half way down a 3m deep keel in a
cutaway.

Please explain what you mean by "trawler" (fishing or yacht)
and "cutaway" and
what the depth of the prop has to do with it.

To be exact, a Brixham Trawler, a 75ft gaff rigged ketch,
designed with a powerful rig for sail trawling. The keel is
straight from stem to stern, about 1m draft at the stem, 3m draft
at the stern. The rudder is mounted 20degrees off vertical. The
aft hull is flat, wide beamed, and lifts above waterline at the
rudder post. The prop is mounted 1.5m deep, in a 60cm (2ft!) arc
cut into the keel just forward of the rudder hinge. The effect is
that the reverse wash of the prop runs down each side of a
vertically straight keel - which I assume kills the spiralling of
the prop wash on both sides equally.

OK, think I see what you're saying.
First off, I used to run a 65 foot boat with a similar configuration and
remember a beautiful old 45' ketch with the same thing ... both had large
degrees of "propwalk".
Secondly, I think we may have different views of what is the major cause of
prop walk (I attribute it to the pitch of the blades pulling to a greater
degree on the "down stroke" side of the revolution, than the "upstroke
side").

Whereas most modern vessels
have the upper part of their prop wash losing energy to the hull
bottom through friction, and no other interference.

I think we're on the same track but drawing different conclusions.


I can see where this stuff together would cut down propwalk. A
Kort nozzle can
be found on fishing boats, but your main application will be
tugs. It's a
shaped cylinder, generally attached to the hull, which
surrounds the prop,
entirely.
It's main function is to increase "bollard pull", but because
it surrounds the
prop, the prop can not "pull" to one side (propwalk) since all
thrust is
directed out the nozzle, either ahead or astern.

I think the key factor here is the cruciform blades supporting
the cylinder in front of the prop, which act as flow
straighteners. No spiral flow along the hull = no prop walk.

In the case of a Kort nozzle, there are no cruciform blades supporting the
nozzle in front of the prop. The nozzle is "hung" beneath the hull and left
as
clear as possible in front to aid a clear flow to the prop (kinda like the
nacelle surrounding a jet engine).


If the prop's deep, but close to a horizontal surface (the hull)
you'll get good prop walk. Because the hull, through friction,
kills the lateral velocity of the spiralling wash on top, but the
lower spiral rushes off, giving you asymmetric reverse thrust.

Here I have to disagree that the prop has to be close to the hull when deep
to
get a good degree of walk .... take for instance any twin screw vessel where
the props are away ... you still get good prop walk (Before some one says
this
is due to off center thrust .... shift to inboard turning wheels and you'll
see
a marked difference).

Paddle wheel effect if you like. If the prop is well clear of the
hull, just look at the shaft supports to design prop walk out. If
you've got a vertical blade supporting the shaft, stick a
balancing skeg below it. Keeps the ropes clear too.

BG Why would I want to design "propwalk" out? "Propwalk" is my friend!

Shen

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/28/2004 15:26 Pacific Standard Time
Message-id:

you are right about one thing, schlackoff. I don't have any personal
experience
with hermaphordites. you have me beat on that score.

I believe it's spelled "hermaphrodite", and I've only sailed on one such Brig
....... oh! Wait ... You're talking about your sexual proclivities again.
Jaxoff, you need to get yer mind outa da gutter.

Shen

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/28/2004 15:22 Pacific Standard Time
Message-id:

Never hoid of this Feynman character ...

here you go. 467,000 hits for you read. next time you will know who this
famous man was.

http://www.google.com/search?hl=en&i...59-1&q=feynman

btw schlackoff, Feynman won his Nobel prize in physics long ago, which he got
his before you'll get yours.

....but can you or this Feynman handle a boat? We know you can't, and if Mr
Feynman can't apply his scientific "stuff" to boat handling, what good is he,
his nobel prize, or all his scientific papers to this discussion?

Sorry Jax, I larn't my boat handling by doing, not reading books.
My offer will increase to $600/hr at the end of the day, simply because you're
a useless aggravation and I know I'll need a new pair of steel toed shoes,
after the first hour, to get your attention.

Shen

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/28/2004 15:17 Pacific Standard Time
Message-id:

I attribute it to the pitch of the blades pulling to a greater
degree on the "down stroke" side of the revolution, than the "upstroke side"

This is only true -- for a fixed blade prop -- when the shaft is angled AND
the
boat is moving.

Wrong on every point. Spout all the scientific crap you want .... can be fixed
or variable pitch, horizontal or angled, moving or at the initial start before
moving. .... what's most important is what the boat handler can see or feel.

A variable pitch prop will generally cause walk even at so called zero
pitch(the degree may vary, but it will still be a factor you need to address);
a boat with a horizontal shaft will have prop walk, just like one with an
angled shaft (the degree may vary, but it will still be a factor you have to
address); immediately upon turning the prop, before you get sternway, you will
get "propwalk"(the degree may vary, but it will still be a factor you will have
to address).
Fer cripes sake, Jax, take some courses, get some experience .....hell, I'll
give you a bargain basement rate .... $800/hr.

Shen