Subject: Thrust vectoring
From: "JimB"
Date: 03/27/2004 04:21 Pacific Standard Time
Message-id: Sre9c.1164$aQ3.634@newsfe1-win
otnmbrd wrote in message
nk.net...
Single screw .... With full left rudder, kick ahead, bow will
swing to
port .... due mainly to rudder and some prop walk (right hand
prop).
With rudder hard left, kick astern, stern will swing to port
.... all
prop walk, has nothing to due with rudder placement(rudder
could be hard
left or hard right, initial affect will be the same).
The only way to shield a prop from prop walk, that I know of is
a Kort
Nozzle or similar shield.
There's very little prop walk on traditional wood trawlers, when
the prop is set almost half way down a 3m deep keel in a cutaway.
Please explain what you mean by "trawler" (fishing or yacht) and "cutaway" and
what the depth of the prop has to do with it.
Also, many Greek fishing vessels (enormously over-engined with
old bus engines 300hp driving a 30ft caique) to put long skegs in
front of the prop and big lateral plates extending sideways at
water level to stop air being drawn into these mammoth blades.
This also keeps nets and ropes clear, and seems to minimise prop
walk.
Interesting.
I don't know a Kort nozzle, but if it's a protective cylinder
around the prop with a skeg and cross shaped blades supporting it
in front, that's what I meant by 'shield'. Some old, single
engined tugs used to use these and I suspect the Greek approach
is a half way house.
I can see where this stuff together would cut down propwalk. A Kort nozzle can
be found on fishing boats, but your main application will be tugs. It's a
shaped cylinder, generally attached to the hull, which surrounds the prop,
entirely.
It's main function is to increase "bollard pull", but because it surrounds the
prop, the prop can not "pull" to one side (propwalk) since all thrust is
directed out the nozzle, either ahead or astern.
Also on hydrofoils, where the prop is 2m deep with no hull
interference in sight. But that's a bit exotic, since most
hydrofoils are twin screw.
JimB
Not sure why this reference to depth of a prop in relation to a hull. I may be
reading you wrong, but, for instance, take a single screw ship where the prop
is generally set fairly deep on the hull..... they tend to torque to a
fairtheewell.
Shen