Owner, Green Bay Packers
Join Date: Sep 2006
Location: SW Michigan
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I stand out on the bridge wing and give my commands to the helmsman and mate in the wheelhouse. Oops...actually i sit thwartships on my small boat and look in the most relevant direction, relieing on perripheral vision to catch the bow swing.
Underwater hull configuration as well as prop location dictate the amount of prop walk along with propeller pitch. With a right hand screw or wheel, the wheel throws water out and forward, against the starboard side of the hull while going astern. This, combined with the semi-vacuume of water the wheel has caused to port, by pulling the water into itself, causes the stern to walk. The shallower the water and the slower the boat is moving, the greater the prop walk.
When going ahead or turning the wheel clockwise, the prop throws the water out to port and aft, where-there is no hull to strike, as well as a rudder to flow over providing directional stability to the prop wash.
The obvious solution that minimizes the effect is an adjustable pitch propeller. By varying the pitch of the propeller, instead of propeller shaft speed, one can go ahead or astern slowly while minimizing the walking of the wheel. This set-up is fairly common on your gas turbine equipped sea-going vessels,usually upwards of 50,000 tons displacement, where the addition of a half million dollar wheel and attendant hydraulic control system is not felt to be an onerous expense.
The only really practical thing one can do to minimize prop walk on a really crabby boat is to reduce the pitch of the prop, which also will reduce the overall speed of the vessel under power, a tough trade-off. Some boats have the propeller shaft offset from the center line of the vessel, that is, not running directly fore and aft, to minimize the effect. I'm not sure that this is an area that has reached an exact science or effectiveness.
On the other hand, the vast majority of us would have the devil's own time docking without prop walk. Once one knows one's boat, and how much she walks, it can be an indispensable manoeuvering aid, at speeds where it has much more effect than the rudder alone.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.