Subject: Thrust vectoring
From: "JimB" j
Shen44 wrote in message

OK, think I see what you're saying.
First off, I used to run a 65 foot boat with a similar
configuration and
remember a beautiful old 45' ketch with the same thing ... both
had large
degrees of "propwalk".

Interesting. Some of the older boats had engines added later, of
course, and sensibly had prop shafts installed with an offset so
you could remove the shaft without taking the rudder off. That
changed the prop wallk picture a bit!

True There are many varying degrees of propwalk, for varying reasons (offsets,
kort nozzles, rope guards, to name a few). I normally board a boat and find out
type and rotation of prop to determine expected direction of walk, then as soon
as possible, if it's new to me I'll try to create a situatuion to test it out.
I've learned to expect a certain direction and amount of walk for some boats,
but always keep in mind that sometimes, especially on some boats they may walk
opposite to the expected (normally this will be a wind, current, or existing
turn situation, but not always.). .... at any rate, expect it, test it, and
then be ready for the unexpected.


Secondly, I think we may have different views of what is the
major cause of
prop walk (I attribute it to the pitch of the blades pulling to
a greater
degree on the "down stroke" side of the revolution, than the
"upstroke side").

OK. The only certainty about prop walk is that it must be caused
by the prop in reverse squirting more water to one side of the
boat than the other. We could discuss the mechanism for ages -
but there wouldn't be much practical use to that unless we were
designers!

Again true, although there is still prop walk when going fwd, it's just not
normally as noticeable.

BG Why would I want to design "propwalk" out? "Propwalk" is
my friend!

Especially pulling the stern in as you come alongside.... bit of
a sod when it's the wrong side though.

G Can also be used when docking the other side too, to stop the stern coming
alongside as you stop.
There is no doubt, that at times, prop walk is a pita, because it is contrary
to what you want and need to do, but in a high percentage of cases, it can be
made to work for you.

Shen