push vs pull vis a vis rudders
 

Rodney Myrvaagnes wrote in message
...
On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"
wrote:


[snip]
I'm trying to square Jax's flat 'nada' with rudder kick I've
observed, and an impression that the rudder direction affects
boat yaw when in reverse and not moving,
[snip]

I have observed the rudder kick in reverse, but only with the
boat in
motion. Does yours do this when tied to the dock?

It did in two previous vessels I've skippered, both of which had
big props a small distance from big rudders. Both also had
tillers, so force feedback was not hidden by gearing. It wasn't
big, but was apparent.

JimB

push vs pull vis a vis rudders
 

Steven Shelikoff wrote in message
...
On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"

So I hung the spatula just behind the fan. Lo and behold, the
same
thing happens but just a little less. When I rotate the
spatula to the
left, there is a noticable *left* motion to the blade... i.e.,
it's not
only drawn forward into the blade but it also moved to the left
from
where it was when the spatula blade was perpendicular to the
fan. When
I turn it to the right, the spatula swings to the right.

Steve, that was the experiment I first did. Then I realised that,
to yaw the boat, I had to look solely at lateral force. To do
this I had to constrain the card so that it could only hinge
laterally (no fore and aft motion permitted). This is where the
bits of wire came in. The card had a bit of wire attached rigidy
to the top, sticking at 45 deg horizontal angle to the card. The
card end of the wire bent down to stop the card swinging around
the wrong end of the wire. I hung the card (your spatula I
guess!) through two loops (hinges) first mounted parallel to the
centre line of the fan, then at right angles.

This gave a different result, very little lateral swing, lots of
fore and aft swing. Of course (a weakness in the experiment) it
didn't check for any lateral force effects on the fan of changes
in airflow, nor was it a very good representaion of relative
sizes of prop and rudder.

That proves to my satisfaction that if the rudder is close
enough to the
prop, it's direction will have some effect on the motion of the
boat
when you throw it in reverse even before the boat starts making
sterway.

My initial conclusion too, until I changed the hinging
arrangement.

JimB

push vs pull vis a vis rudders
 

Steven Shelikoff wrote in message
...
On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"

So I hung the spatula just behind the fan. Lo and behold, the
same
thing happens but just a little less. When I rotate the
spatula to the
left, there is a noticable *left* motion to the blade... i.e.,
it's not
only drawn forward into the blade but it also moved to the left
from
where it was when the spatula blade was perpendicular to the
fan. When
I turn it to the right, the spatula swings to the right.

Steve, that was the experiment I first did. Then I realised that,
to yaw the boat, I had to look solely at lateral force. To do
this I had to constrain the card so that it could only hinge
laterally (no fore and aft motion permitted). This is where the
bits of wire came in. The card had a bit of wire attached rigidy
to the top, sticking at 45 deg horizontal angle to the card. The
card end of the wire bent down to stop the card swinging around
the wrong end of the wire. I hung the card (your spatula I
guess!) through two loops (hinges) first mounted parallel to the
centre line of the fan, then at right angles.

This gave a different result, very little lateral swing, lots of
fore and aft swing. Of course (a weakness in the experiment) it
didn't check for any lateral force effects on the fan of changes
in airflow, nor was it a very good representaion of relative
sizes of prop and rudder.

That proves to my satisfaction that if the rudder is close
enough to the
prop, it's direction will have some effect on the motion of the
boat
when you throw it in reverse even before the boat starts making
sterway.

My initial conclusion too, until I changed the hinging
arrangement.

JimB

push vs pull vis a vis rudders
 

Brian Whatcott wrote in message
...
On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"
wrote:
....

Asking for explanations from experimental rigs is the royal
road to
progress. Congratulations!

Limitations of the experiment:
It didn't check for associated force changes at the fan
The scale of 'rudder' against fan size is way out
The wire had a little flexibility
Fag ends produced smoke which rose too fast
Reynolds numbers were wrong.

And, just in case you mis-understood, my hinges were pendulum
hinges which did not allow the 'rudder' to rotate around its
vertical axis (except in the 'rudder kick' experiment). They only
allowed pendulum movement laterally, or when re-oriented, fore
and aft (subject to wire flexibility).

If a hinge surface is hinged more than about 1/4 aft of its
present
leading edge it is unstable in the fluid flow. ('rudder kick')

Agreed, and not necessarily a proof that there's a net force at
right angles to the centreline of the boat (my earlier
assumption)

If a surface *is* hinged about 1/4 from the leading edge, it
can
still break into oscillations which are quickly destructive,
unless
the mass is balanced closer to the hinge line.

Good old flutter.

If a FLAT surface is inclined slightly ( 20 degrees) to the
fluid
flow, the flow over the 'upper' surface is faster and provides
lower
pressure than the flow over the lower surface. The streamlines
do not
follow the (flat) surface of the test article (of course!),
they kick
up in a smooth curve over the top. This applies to an airfoil
flown
upside down too. The streamlines look similar to the
streamlines
over a right way up foil, but less efficient and with lower
pressure
difference from top/bottom.

If the foil is asymmetric.

Agreed, though Jax seems to challenge the association of local
water speed and pressure. I'll suck him in a bit further on that
one.

It is not necessary for a lump of fluid dividing past the foil
to
join up again after it has passed..
When providing lift, the lump of fluid does not join up again,
in
fact.

We seem to agree on basic aerodynamics. I'm looking forward to
hearing more about modern advanced fluid dynamics from Jax in the
'lift over foils' thread. Perhaps you can act as moderator?

JimB

push vs pull vis a vis rudders
 

Brian Whatcott wrote in message
...
On Wed, 31 Mar 2004 10:20:59 +0100, "JimB"
wrote:
....

Asking for explanations from experimental rigs is the royal
road to
progress. Congratulations!

Limitations of the experiment:
It didn't check for associated force changes at the fan
The scale of 'rudder' against fan size is way out
The wire had a little flexibility
Fag ends produced smoke which rose too fast
Reynolds numbers were wrong.

And, just in case you mis-understood, my hinges were pendulum
hinges which did not allow the 'rudder' to rotate around its
vertical axis (except in the 'rudder kick' experiment). They only
allowed pendulum movement laterally, or when re-oriented, fore
and aft (subject to wire flexibility).

If a hinge surface is hinged more than about 1/4 aft of its
present
leading edge it is unstable in the fluid flow. ('rudder kick')

Agreed, and not necessarily a proof that there's a net force at
right angles to the centreline of the boat (my earlier
assumption)

If a surface *is* hinged about 1/4 from the leading edge, it
can
still break into oscillations which are quickly destructive,
unless
the mass is balanced closer to the hinge line.

Good old flutter.

If a FLAT surface is inclined slightly ( 20 degrees) to the
fluid
flow, the flow over the 'upper' surface is faster and provides
lower
pressure than the flow over the lower surface. The streamlines
do not
follow the (flat) surface of the test article (of course!),
they kick
up in a smooth curve over the top. This applies to an airfoil
flown
upside down too. The streamlines look similar to the
streamlines
over a right way up foil, but less efficient and with lower
pressure
difference from top/bottom.

If the foil is asymmetric.

Agreed, though Jax seems to challenge the association of local
water speed and pressure. I'll suck him in a bit further on that
one.

It is not necessary for a lump of fluid dividing past the foil
to
join up again after it has passed..
When providing lift, the lump of fluid does not join up again,
in
fact.

We seem to agree on basic aerodynamics. I'm looking forward to
hearing more about modern advanced fluid dynamics from Jax in the
'lift over foils' thread. Perhaps you can act as moderator?

JimB

push vs pull vis a vis rudders
 

Expert is a relative term. Compared to the majority of this news
group, he is a profesional expert in fluid flow. Different types
of fluid flow compared to those you were thinking of, maybe. I
speculate; hydraulics perhaps? A mere tool to him?

self-proclaimed "expert" or not, he made statements to this group as fact that
were not fact. And he did it from the get-go in a fashion to tell one and all
he was b/sing.

he is an electrical engineer by training, training he received in the later
1960's in a country with more sheep than people.

in an email to me he tried to justify his stance by saying something to effect
that the friction in the rudder bearing made the difference.

I suspect the good professor had something to contribute, but he claim b/sing,
so much I so I figureed someone hijacked his email address and he didn't know.

push vs pull vis a vis rudders
 

Expert is a relative term. Compared to the majority of this news
group, he is a profesional expert in fluid flow. Different types
of fluid flow compared to those you were thinking of, maybe. I
speculate; hydraulics perhaps? A mere tool to him?

self-proclaimed "expert" or not, he made statements to this group as fact that
were not fact. And he did it from the get-go in a fashion to tell one and all
he was b/sing.

he is an electrical engineer by training, training he received in the later
1960's in a country with more sheep than people.

in an email to me he tried to justify his stance by saying something to effect
that the friction in the rudder bearing made the difference.

I suspect the good professor had something to contribute, but he claim b/sing,
so much I so I figureed someone hijacked his email address and he didn't know.

push vs pull vis a vis rudders
 

On 01 Apr 2004 03:15:26 GMT, (JAXAshby) wrote:

yeah, sure. rudder right, tranny forward, throttle forward and what
happens
....???

Most times you go right. Sometimes you go left. If you've never gone
left when doing the above, you need some more experience.

sherr tells us the more experience he has the more he don't know which way
his
boat is gonna go thusly:

Joxie, say it ain't so! With all your claimed sea experience you've
never had the boat turn in a different direction than where you had the
rudder pointed? Oh, that's right. You're just a hired hand with no
helm experience. If you had any time at the helm in poor conditions
you'd know just how foolish you're looking right about now.

schlackoff, when the wind and/or current was pushing me one way or the other I
knew it long before I put the boat in forward or reverse.

Of course. Just like you *should* know about prop walk but apparently
don't if you don't know which way you boat will turn when you throw it
in reverse.

Steve

push vs pull vis a vis rudders
 

On 01 Apr 2004 03:15:26 GMT, (JAXAshby) wrote:

yeah, sure. rudder right, tranny forward, throttle forward and what
happens
....???

Most times you go right. Sometimes you go left. If you've never gone
left when doing the above, you need some more experience.

sherr tells us the more experience he has the more he don't know which way
his
boat is gonna go thusly:

Joxie, say it ain't so! With all your claimed sea experience you've
never had the boat turn in a different direction than where you had the
rudder pointed? Oh, that's right. You're just a hired hand with no
helm experience. If you had any time at the helm in poor conditions
you'd know just how foolish you're looking right about now.

schlackoff, when the wind and/or current was pushing me one way or the other I
knew it long before I put the boat in forward or reverse.

Of course. Just like you *should* know about prop walk but apparently
don't if you don't know which way you boat will turn when you throw it
in reverse.

Steve

push vs pull vis a vis rudders
 

On Thu, 01 Apr 2004 13:01:41 GMT, (Steven Shelikoff)
wrote:

On 01 Apr 2004 03:15:26 GMT, (JAXAshby) wrote:

yeah, sure. rudder right, tranny forward, throttle forward and what
happens
....???

Most times you go right. Sometimes you go left. If you've never gone
left when doing the above, you need some more experience.

sherr tells us the more experience he has the more he don't know which way
his
boat is gonna go thusly:

Joxie, say it ain't so! With all your claimed sea experience you've
never had the boat turn in a different direction than where you had the
rudder pointed? Oh, that's right. You're just a hired hand with no
helm experience. If you had any time at the helm in poor conditions
you'd know just how foolish you're looking right about now.

schlackoff, when the wind and/or current was pushing me one way or the other I
knew it long before I put the boat in forward or reverse.

Of course. Just like you *should* know about prop walk but apparently
don't if you don't know which way you boat will turn when you throw it
in reverse.

And in those conditions, just like prop walk in reverse, you won't know
which way an unfamiliar boat will turn when you put the rudder one way
or another. In all cases, that doesn't mean the rudder has no effect.
It only means it can't overcome other effects

Steve