Jax,

I may not be the brightest bulb in the box, and the last physics course
I took was well over twenty years ago (I still break out in a cold sweat
when I hear the words "Virial Theorem"), so if you can explain it to me
I'd appreciate it.

How does the rudder (or the rudder stock & pintles through which the
force is applied to the hull) know whether the water flowing past it is
being pushed or pulled?

Now if you want to argue that the water flow across the rudder is so
small that the effect of the rudder is overpowered by the prop walk,
that I can buy. But to say that the water flowing past the rudder (and
being deflected by it has no effect because it's motion was started by
some mysterious sucking force makes no sense.

Because the water column being pushed aft when in forward is of constant
diameter (at least in gross terms across the distances we are toaling
about), the velocity in the column is for practical purposes constant.
resulting in a high velocity stream being deflected by the rudder and a
large resultant lateral force.

In reverse, however, there is no such water column aft of the prop. The
water is being sucked in from all directions and thus it's velocity
falls off as the square of the distance from the prop (again, we are
taling in gross terms here). This results in a comparatively slow, but
non-zero velocity as it passes the rudder. Movement of the water
(regardless of it's cause) past the rudder, and its' being deflected by
it causes a lateral force.

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.


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.










--
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