"JAXAshby" wrote in message
...
an object placed on the "suction side" of a propeller
will

there is no force in natural called "suction". Everyone with even one
semester
in physics knows that.

how many semesters did you say you had, jeffies?

There may not be a force called "suction" but I did not use the word in that
context. "Suction Side" is a commonly used engineering term, used in the
context of both propellers and compressors. If you had the even most basic
knowledge of refrigeration (you claimed family in the business) you would know
that. You've just demonstrated that you're a complete fraud, jaxie. But we all
knew that.

Subject: Thrust vectoring
From: (JAXAshby)

Jaxass, your comment has nothing to do with what he's been discussing.
It is, however, very basic knowledge, which I'm surprised you know...... it can
also be applied to moving ahead, but that's probably too much "input" for you
for one day.

Shen

schlackoff, you were told to never post in English. Adults are posting and
they use big words like "docking" and such.

Huh? What does that have to do with what he is saying .... "back up" is not
being discussed.

Shen


careful. you *must* be moving through the water for a rudder to be
effective
when trying to back up.

Thanks. One of the things I tend to talk about is the potential
advantage of using rudders when twisting (swivel) as it tends to help
when you work into how you need to set your rudders to "walk".

o

On 25 Mar 2004 19:07:46 GMT, (JAXAshby) wrote:

It is a fact of physics that
you can NOT control using rudder by *pulling* water over it. you MUST push.

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

Absolutely not true.

If there is water moving past the rudder, regardless of direction or
cause, it can be used to create a directed thrust simply by angling
the rudder away from the flow direction.

The confusion arises because the prop in forward pushes a large flow
across the rudder, whereas the prop in reverse pulls only a relatively
small amount of water across the rudder. Small, but not zero.

You don't need a degree in physics to understand this, just a little
common sense. Richard Feynman would no doubt find the discussion
amusing however.

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.

wayne, you are out of your league.

*push* is required under the laws of physics. If you can't see that, just take
Feynman's word for it.

It is a fact of physics that
you can NOT control using rudder by *pulling* water over it. you MUST
push.

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

Absolutely not true.

If there is water moving past the rudder, regardless of direction or
cause, it can be used to create a directed thrust simply by angling
the rudder away from the flow direction.

The confusion arises because the prop in forward pushes a large flow
across the rudder, whereas the prop in reverse pulls only a relatively
small amount of water across the rudder. Small, but not zero.

You don't need a degree in physics to understand this, just a little
common sense. Richard Feynman would no doubt find the discussion
amusing however.

Thanks ....comments interspersed:

Rod McInnis wrote:
With this in mind, for those with twin screw boats, if I told you that
rudders were important tools of boat handling, but not to be considered
for steering, rather for "thrust vectoring", when maneuvering around a
dock, etc., when kicking an engine ahead, both positive and negative
...... would you understand what I was saying?



No, I would think that most people would be more confused.

Why?


To begin with, I would start by pointing out that there is a big difference
between how an inboard reacts and how I/Os or outboards react. There is
also a big difference between what I call "large rudder" and "small rudder"
boats.

Sorry, I should have made it more specific that I was just talking about
"inboards" not IO's or outboards. On inboards, there can be "large
rudder" as well as "small rudder" boats (generally they tend toward
"small" but it's "not written in stone"). It's also interesting that few
talk about type of rudder when talking about it's "size" (can also be
read as "power").

A typical sail boat has a "large rudder" which becomes effective, in either
forward or reverse, as soon as the boat is making way.

A typical power boat has a "small rudder" which either needs a significant
amount of boat speed or to have the prop pushing water past it. These
rudders are generally ineffective in reverse.

see above


The basic concept of twin engine inboards is that you consider the rudder to
only be a factor when the engine is in forward. Ignore it for the engine in
reverse.

Interesting comment that I think a few have made. To check on myself, I
went back to my original post to see if I'd indicated anywhere that I
was applying this "thrust vectoring" to astern "kicks" ... I wasn't, and
in fact specifically stated "when kicking an engine ahead", so I don't
know where your last two sentences are coming from.
Hmmmm I see something ... "both positive and negative", refers to rudder
angle when doing, say, a twist or walk.

otn

On Thu, 25 Mar 2004 02:07:31 GMT, otnmbrd
wrote:

For years, on occasion, I've have been involved with teaching someone
boat handling, using single and/or twin screw inboards.....if I told you that
rudders were important tools of boat handling, but not to be considered
for steering, rather for "thrust vectoring", when maneuvering around a
dock, etc., when kicking an engine ahead, both positive and negative
...... would you understand what I was saying?

otn

Probably not, judging by one or two of the responses here.
Perhaps it would be easier for you to demonstrate the effect of
sucking a fluid past a board placed in the forward stream line.

Take a hand vacuum (I used a Bissett) and close to the suction nozzle,
place a sheet of paper parallel to the air flow into the nozzle.
Place the edge quite close to the nozzle's side.
You will see the paper move sidewards towards the airflow into the
vacuum if the flow speed is unequal on each side of the paper.
Bernouilli of course. The effect is quite small, but readily visible.

Faster flow leads to lower pressure, of course.
Extending the demo to the rudder placed behind the propellor spinning
in reverse to show the small side force on the rudder should then be
easier to communicate, I'd think.

Brian Whatcott

You're absolutely wrong about this jaxie. Feynman would think you're a complete
fool for invoking his "sprinkler paradox" in this case. The boat is not turned
directly by the propeller, it is turned because a water flow is pressing against
the rudder. "Push" and "pull" are irrelevant, and the water flow could even
come from a current, or the wash from another boat. For a variety of reasons,
the affect is far more powerful in foreword, but it is still there in reverse.

USSailing, and Boat/US both describe this on their websites.
http://www.videos.sailingcourse.com/...pring_line.htm
http://www.boatus.com/seaworthy/swlines.asp
And the Coast Guard
http://www.uscg.mil/hq/g-o/cgaux/Pub...crew/ch10d.pdf



"JAXAshby" wrote in message
...
wayne, you are out of your league.

*push* is required under the laws of physics. If you can't see that, just
take
Feynman's word for it.

It is a fact of physics that
you can NOT control using rudder by *pulling* water over it. you MUST
push.

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

Absolutely not true.

If there is water moving past the rudder, regardless of direction or
cause, it can be used to create a directed thrust simply by angling
the rudder away from the flow direction.

The confusion arises because the prop in forward pushes a large flow
across the rudder, whereas the prop in reverse pulls only a relatively
small amount of water across the rudder. Small, but not zero.

You don't need a degree in physics to understand this, just a little
common sense. Richard Feynman would no doubt find the discussion
amusing however.

Thanks. G Wasn't really interested in how you reacted to others
responses, only in how YOU reacted.
As for the rest, you seem to have also grabbed onto the "reverse"
aspect, which is NOT what I was discussing at all. I repeat, "When
kicking an engine ahead" Thrust vectoring does not apply when going
astern, unless G you have Flanking Rudders.... which is another story
entirely.

otn

Brian Whatcott wrote:

Probably not, judging by one or two of the responses here.
Perhaps it would be easier for you to demonstrate the effect of
sucking a fluid past a board placed in the forward stream line.

Take a hand vacuum (I used a Bissett) and close to the suction nozzle,
place a sheet of paper parallel to the air flow into the nozzle.
Place the edge quite close to the nozzle's side.
You will see the paper move sidewards towards the airflow into the
vacuum if the flow speed is unequal on each side of the paper.
Bernouilli of course. The effect is quite small, but readily visible.

Faster flow leads to lower pressure, of course.
Extending the demo to the rudder placed behind the propellor spinning
in reverse to show the small side force on the rudder should then be
easier to communicate, I'd think.

Brian Whatcott

On 25 Mar 2004 22:00:48 GMT, (JAXAshby) wrote:

wayne, you are out of your league.

*push* is required under the laws of physics. If you can't see that, just take
Feynman's word for it.

I have to agree with Jax on this one. Why else do you think all
airplanes have the propellor in the back.

Steve