For years, on occasion, I've have been involved with teaching someone
boat handling, using single and/or twin screw inboards.
Naturally, (especially on twin screw+) the issue of rudder use arises (
from here we will consider this a twin screw+ discussion).
So that everyone knows, I am a STRONG proponent of rudder use, but I
understand many of the arguments against (G just don't agree with all
of them or feel the argument doesn't really address the issue).
In all of my discussions, I have had a problem with the term "steering",
as in "the boats moving too slow to steer with rudders", or "rudders are
not effective at these speeds".
At any rate, I knew I was never able to explain my point clearly and
concisely.
Recently, for some unknown reason, I remembered a TV show on jet
fighters which discussed (I believe) thrust vectoring, and it dawned on
me that this may be just the term to describe what I am trying to get
across to those I am teaching.
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?

otn

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?

I would know you are bull****ting, for pulling water over a rudder with a prop
does not -- and can not under the laws of physics -- affect the direction a
boat is moving.

otn

Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/24/2004 19:39 Pacific Standard Time
Message-id:

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?

I would know you are bull****ting, for pulling water over a rudder with a
prop
does not -- and can not under the laws of physics -- affect the direction a
boat is moving.

otn

Since I know Otn has jaxass killfiled, I'll quote this nonsense so otn can read
it.

Shen

Otn has jaxass killfiled,

is over the nee a blockhead?

Interesting. I can't think of too many boats that "pull" water over a
rudder for steering, except in reverse, and this is well known to be,
generally, of little effect.
Of course, considering the source of that statement, we realize it has
no value, other than to say he didn't understand what I was saying, nor
does he have any knowledge of the subject.
G I'll call that a "negative", with reservations.....
Come-on group, I'm looking for some pos/neg responses from people with
some knowledge and experience, not jaxasses .....

otn

Shen44 wrote:
Subject: Thrust vectoring
From: (JAXAshby)
Date: 03/24/2004 19:39 Pacific Standard Time
Message-id:

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?

I would know you are bull****ting, for pulling water over a rudder with a
prop
does not -- and can not under the laws of physics -- affect the direction a
boat is moving.

otn


Since I know Otn has jaxass killfiled, I'll quote this nonsense so otn can read
it.

Shen

In article .net,
otnmbrd wrote:

For years, on occasion, I've have been involved with teaching someone
boat handling, using single and/or twin screw inboards.
Naturally, (especially on twin screw+) the issue of rudder use arises (
from here we will consider this a twin screw+ discussion).
So that everyone knows, I am a STRONG proponent of rudder use, but I
understand many of the arguments against (G just don't agree with all
of them or feel the argument doesn't really address the issue).
In all of my discussions, I have had a problem with the term "steering",
as in "the boats moving too slow to steer with rudders", or "rudders are
not effective at these speeds".
At any rate, I knew I was never able to explain my point clearly and
concisely.
Recently, for some unknown reason, I remembered a TV show on jet
fighters which discussed (I believe) thrust vectoring, and it dawned on
me that this may be just the term to describe what I am trying to get
across to those I am teaching.
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?

otn


I believe I know what you're talking about, having learned how to "walk"
a cat sidewards (using prop wash against rudder, and prop walk from the
reversed engine) but I don't think I would understand "thrust vectoring"
in that context unless I'd done it. It IS, to a certain extent, of
course.

Then again, I may be thinking too far in advance. If you're talking
about swinging the bow about, I am thinking "torque" or possibly
"balanced (or imbalanced) opposing forces".

I don't think you're simply talking about the wash over the rudder. That
is clearly thrust vectoring, but should be easy enough to explain as
"kicking the ass over".

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

Jere Lull wrote in message
...
In article
.net,
otnmbrd wrote:

I don't think you're simply talking about the wash over the
rudder. That
is clearly thrust vectoring, but should be easy enough to
explain as
"kicking the ass over".

I like Jere's approach. It correctly describes both phenomena you
get using rudder with power; first, a rotation, secondly, a
lateral movement.

When teaching, I've found it useful to separate the two
phenomena.

First, how to point the boat. If you're static, that's using one
engine ahead and one astern to swivel around a point with rudder
neutral. If you're moving forward significantly (or aft) that's
using rudder or differential engine to steer.

Second, how to shift the boat (or part of it) bodily sideways.
That's using wind, and/or prop walk, and/or power with rudder
(the other engine being used to control the degree of fore/aft
movement), and/or bow thruster. The last three I certainly
understand as 'thrust vectoring' (I'm familiar with the term as
an ex VTOL pilot, and most numerate people would be OK with
'vectoring').

When teaching, though, I'd test my pupil's understanding of the
phrase before using it. After all, the student may be numerate -
as an accountant - rather than a physics major. And 'kicking ass'
does have a nice ring to it . . .

JimB, Yacht Rapaz, sadly, for sale to buy that nice new Greek
house:
http://www.homepage.ntlworld.com/jim...cification.htm

Hello otn,

I wasn't quite sure what you were driving at until I read your last
sentence and then it all became crystal clear. So the answer is "yes"
I would understand what you were saying and "yes" it would help me
understand the concept. But even though the term "thrust" is easy for
most people to understand, the concept of a "vector" (magnitude and
direction) may not be. But only you know who your target audience is,
and whether they would understand what a vector is. Hope this helps,

Bob Whitaker
"Free Spirit"


otnmbrd wrote in message hlink.net...
For years, on occasion, I've have been involved with teaching someone
boat handling, using single and/or twin screw inboards.
Naturally, (especially on twin screw+) the issue of rudder use arises (
from here we will consider this a twin screw+ discussion).
So that everyone knows, I am a STRONG proponent of rudder use, but I
understand many of the arguments against (G just don't agree with all
of them or feel the argument doesn't really address the issue).
In all of my discussions, I have had a problem with the term "steering",
as in "the boats moving too slow to steer with rudders", or "rudders are
not effective at these speeds".
At any rate, I knew I was never able to explain my point clearly and
concisely.
Recently, for some unknown reason, I remembered a TV show on jet
fighters which discussed (I believe) thrust vectoring, and it dawned on
me that this may be just the term to describe what I am trying to get
across to those I am teaching.
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?

otn

Interesting. I can't think of too many boats that "pull" water over a
rudder for steering, except in reverse, and this is well known to be,
generally, of little effect.

zero effect. none.

On 25 Mar 2004 01:32:19 -0800, (Bob Whitaker)
wrote:
I wasn't quite sure what you were driving at until I read your last
sentence and then it all became crystal clear. So the answer is "yes"
I would understand what you were saying and "yes" it would help me
understand the concept. But even though the term "thrust" is easy for
most people to understand, the concept of a "vector" (magnitude and
direction) may not be. But only you know who your target audience is,
and whether they would understand what a vector is.
===============================

From a teaching standpoint, I think it might be more clear, and to a
wider audience, if you referred to the concept as "directed thrust",
i.e., using the rudder to direct the prop thrust to port or starboard.
It means the same thing but to me it's more intuitive.

I think the most difficult concept to visualize is "prop walk". It's
not instantly clear what is generating the side force, or in which
direction. Prop walk is important to understand because it seems to
cause much of the consternation when backing a single screw. I like
to think of it as a jet of water created between the prop tips and the
hull, but I'm not sure if that's an accurate visualization or not. If
true, it would imply that deeply mounted props, away from the hull,
should generate less "walk" but I'm not sure if that is valid.

It seems to be a consensus among experienced twin screw captains that
leaving the rudders amidship is good practice for most maneuvers.
There are exceptions of course but having the rudders amidship leads
to more predictable response in my experience.

Comments?