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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction
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  #1  
Old 07-21-2011
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Prop walk

I have a new-to-me Bristol 27. It has a cut-away full keel with attached rudder. The prop is in an apature between the keel and rudder. I don't seem to get any prop walk in either direction. Although, I really don't get much thrust in reverse either. Do you think it is normal not to get any prop walk for this design?
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Old 07-21-2011
grumpy old man
 
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Barq:
No, I think you got lucky.
Don't go putting the whammy on yourself!
What kind of prop do you have?
What kind of tip clearance do you have?
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Old 07-21-2011
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Two blades, less pitch, smaller engine.....all these may have an effect. Prop walk is usually subtle. You may have it and not find it to be a problem. I can make my prop walk increase by sudden increases in throtle ("goosing" the engine) or I can have less prop walk with slowly increasing rpm. Take care and joy, Aythya crew

Last edited by CaptainForce; 07-21-2011 at 06:18 PM.
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Old 07-21-2011
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Prop walk is very often far more than subtle and usually does not come and go. Almost all boats with props in apertures experience it to some degree. If Barq doesn't have any then he is fortunate.
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Old 07-22-2011
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Quote:
Originally Posted by bobperry View Post
Prop walk is very often far more than subtle..........
Maybe it is better observed this way than my comment. This got me thinking about the events when prop walk has the least subtle effect for us. When approaching a dock alligned to our starboard, a wharf or face dock, and backing down in reverse to stop our forward momentum; we find it necessary to turn to port, away from the dock, when engaging reverse, to keep the prop walk from turning our bow into the dock. Turning the bow to the dock when stopping alongside to port also keeps us better alligned, but it has more impact on our maneuvering when the dock is to starboard. Take care and joy, Aythya crew
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Old 07-22-2011
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I think I am usually rather gentle with the throttle. Also, I'm not sure if reverse is really engaging as much as it should (Atomic 4). Took an ASA course on an Islander 36. It was actually a nice feeling to be able to suck the stern into the dock using the prop walk. Does in make any difference how long the keel is? Maybe just more lateral resistance with more keel surface? (BTW, the previous owners named the boat 'Circus'. Probably after they tried backing up a few times)
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Old 07-22-2011
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Barq:
When you have a long keel with the rudder attached you can expect very poor control in reverse. I wrote an article on rudders for GOB and I go into the reasons for this. Essentially in reverse you have no turning arm. The center of pressure on the hull is so far aft in reverse that you lose steering power. The best boats in reverse are modern racing boats.
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Old 07-22-2011
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With my long full keel I do best backing into a slip first set from a point that puts my stern aimed well starboard, about 45 degrees, of my desired track and, with intermittant bursts of reverse, my prop walk turns me into the slip. This use of prop walk would not be necessary with a cut-a-way foot or a fin keel that allows effective steerage with the rudder in reverse. Take care and joy, Aythya crew
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Old 07-22-2011
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The type of prop installed makes a tremendous amount of difference in the amount of prop walk in my experience. We went from a fixed three blade power boat type prop that would spin us in a circle if left unchecked with rudder, to an Autoprop which had no discernible prop walk at all. Our current boat has a fixed three blade Campbell sail prop and the prop walk is considerable, but somewhat controllable with increased rpm's and rudder once we are moving.
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Old 07-22-2011
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Thanks for all the input everyone. Bob, love the design series in Good Old Boat.
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