On Mon, 29 Mar 2004 21:00:56 -0700, Keith Hughes
wrote:



Steven Shelikoff wrote:

Consider that it doesn't really matter as long as there is flow of fluid
media over the rudder.

Again, here you're assuming laminar (or at least unidirectional)
flow. When inserted into a laminar flow stream, and angled surface,
such as a rudder, will certainly be subjected to a force related to
the mass of the fluid deflected. Fluid flow on the 'suction' side is
nowhere near laminar, and will in fact be totally non-uniform around
the rudder. All fluid will be redirected immediately upon clearing

That's ok. Fluid on the pressure side of the prop is nowhere near
laminar either and will in fact be totally non-uniform around the
rudder. Yet the rudder still has an effect on the boat's direction.

Consider the fact that fluid drawn over a rudder by a prop may have an
effect on how the stern moves,

It *may* for a brief instant until an equilibrium is reached and the
pressure equalizes on both rudder surfaces (remember, water is *not*
elastic in the way air is, so you can't create a vacuum in water
like you do in air - if you do, you cavitate and dissolve gases come
out of solution until the partial pressures equalize and/or until
water 'fills in the void' and the gases redissolve).

Sure you can create a vacuum in water, just like in air. The only
difference is that water doesn't change it's volume (as much, but it
does a small amoutn) when the pressure changes. There's still a vacuum
though.

And you can certainly create a vacuum in water without cavitation.
Cavitation only occurs if the pressure of the water drops below it's
vapor pressure. There's a whole art/science of creating props that work
without cavitation for use with submarines.

but one that is much less then prop walk.

Many orders of magnitude less IME and IMO.

Especially with an angled propshaft. But there nontheless.

Steve