Thrust vectoring
 

tern will tend to follow the direction
of the top blade of the prop rotation, not the bottom.

yes, that is true. I misspoke by trying to remember which direction my prop
blades are twisted rather than remember which way my engine turns. sorry.

Thrust vectoring
 

Gould 0738 wrote:
Thanks. Actually, I am talking about "wash over the rudder", but I'm
trying to get away from the term "Steering" and it's overall sense of
driving the boat, to concentrate on the effects/advantages of a "kick"
ahead when using or not using the rudder.


From a dead stop, with rudder amidships, you'll experience only a minor amount
of crabbing in the stern when selecting forward. IME. The forward efficiency of
the prop will begin moving the boat ahead so quickly that you can't count on
much useful kick in the stern.

If the wind has you pinned against the dock, you won't realize enough kick to
get the stern free. If the wind is blowing you off the dock, you won't need to
worry about it in any event.

All true .... I should have left "or not using" the rudder out of my
statement above.

otn

Thrust vectoring
 

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".

otn

Thrust vectoring
 

Are you claiming that an object placed on the "suction side" of a propeller
will
not feel an affect, that is it cannot be deflected to one side if it
asymmetrical?

yes, of course I am saying that. you would too if you had the degree in
physics you claim you have.

Thrust vectoring
 

sorry, Dan. don't try to noodle this one out. It is a fact of physics that
you can NOT control using rudder by *pulling* water over it. you MUST push.

lay people often don't that know, for intuitively it doesn't seem "right". but
jeffies has in the past claimed specifically not to be a layperson regarding
physics.

Sorry Jax, sometimes you get it right, but this time your habit of
stating absolutes where not appropriate is showing again. The
underwater lawn sprinkler is an imperfect model for the mechanics of a
boat's prop and rudder. Now, a prop in reverse creates very little
water movement past the rudder compared to one in forward, but very
little is not the same as none. As long as there is water being moving
past and deflected by the rudder there will be some lateral force
generated. Not much in this case, but some. This can be readily
demonstrated as another poster pointed out.

JAXAshby wrote:
The exercise was
repeated in reverse hanging off a bow line, proving (contrary to jaxie's
claim)
the affect works in reverse,


geezus kriste, jeffies, you claim to have a degree in physics and have
NEVER --
to this moment -- heard of classic "under water lawn sprinkler" paradox
that
ALL physics students learn.

Get your wife to explain it to you. It is impossible to steer by *pulling*
water over a rudder with a prop. Can't be done, except when under the
influence of hard drugs.



--
Dan Best - (707) 431-1662, Healdsburg, CA 95448
B-2/75 1977-1979
Tayana 37 #192, "Tricia Jean"
http://rangerbest.home.comcast.net/TriciaJean.JPG

Thrust vectoring
 

gould, NOT unless the boat is making way in all cases where the prop is
*pulling* water over the rudder.

Get your wife to explain it to you. It is impossible to steer by *pulling*
water over a rudder with a prop. Can't be done, except when under the
influence of hard drugs.



It's possible to steer when sternway creates water pressure against the
rudder.

Stick a flat board in the water and try to move it directly forward while
holding it at a fixed angle. :-)

Where can I buy one of those underwater lawn sprinklers that dispenses hard
drugs? :-)



NEVER --
to this moment -- heard of classic "under water lawn sprinkler" paradox that
ALL physics students learn.

Thrust vectoring
 

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?

Thrust vectoring
 

Subject: Thrust vectoring
From: (JAXAshby)

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".

otn

Thrust vectoring
 

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.

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.

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.

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.


Rod

Thrust vectoring
 

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".

otn