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Old 01-25-2012
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Question Prop Walk

Can anyone answer the following:
On single prop sailing vessels, is there any difference in the degree of "prop walk" exhibited by a sail drive equipped vessel, as opposed to a conventional shaft and stuffing box driven vessel?
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Old 01-25-2012
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Good question.... can't say I've ever compared them directly, but it seems to me that the prop itself will be a bigger factor than the strut/shaft vs saildrive configuration. Probably similar lateral plane on both when you take everything into account.

So I'd guess the prop itself in combination with the hull form/keel configuration would be the larger factors.
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Old 01-25-2012
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Yes, most sail drive installations are on modern designs with shortish chord keels and spade rudders. This type of boat rarely has a major prop walk problem anyway. With a sail drive prop walk is almost non existant on this type of boat. The boats with the worst prop walk are boats with props in apertures. I think the aperture sort of funnels and concentrates the flow. If you dangle a line over the stern down by your prop while you are tied up at the dock you will see the line head straight towards the aperture. I am not advising you to do this. I am just saying that I did it.
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Old 01-25-2012
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Quote:
Originally Posted by dstew View Post
Can anyone answer the following:
On single prop sailing vessels, is there any difference in the degree of "prop walk" exhibited by a sail drive equipped vessel, as opposed to a conventional shaft and stuffing box driven vessel?
Yes there's a difference. It's due to the location of the wheel (prop) behind the keel and the size of the rudder. Boats with full or cut back keels are more susceptible to prop walk than a sail drive behind a fin keel. The whole prop walk issue is complicated and related to the hydrodynamic and turbulence created by the wheel over the rudder and is usually the opposite of the wheel rotation. Heavy, full keeled boats suffer more prop prop walk, than lighter, fin keeled, but can even be seen in single screwed power boats.
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Old 01-25-2012
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Wouldn't it make sense the the further a prop is towards the back of the boat the more leverage it could possibly have to to turn the boat to the side.

The closer the prop is to the center of the boat the less leverage it will have.

Since a saildrive boat usually has the prop more forward it should have less propwalk.
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Prop walk is inversely affected by its usefulness in any given situation.
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Old 01-25-2012
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David:
I think that is a big part of it. Good work.
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Prop walk (magnitude) is typically & principally attributed to the distance between the tip of the spinning prop and a surface of the hull, or aperture, etc. ... "tip-clearance" of the prop.

A saildrive usually has the prop mounted on a fixed vertical shaft assembly ... and the prop is held at relative greater distance from the actual hull. If the prop on a saildrive is in close proximity to the hull, then 'prop walk'.
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I thought prop walk was an effect of depth of the lower blade .The larger diameter prop has greater effect. The upper blade bites less (dense?} water so the lower one pulls the boat in its direction of rotation. Imagine the prop half way out so only one blade in the water .Does it in forward too but rudder tends to control the issue.
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Old 01-25-2012
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Rich:
Not sure I agree with your police work there.
The worst cases of prop walk I have known have been with full keel boats with the prop in an aperture.

I also had pretty bad prop walk on one of my boats that had the prop just aft of the keel and quite a distance from the rudder and plenty of tip clearance. I generally allow for 15%.

I'm not saying you are wrong but I think there is more to it than tip clearance. I associate prop vibration and noise with tip clearance.

An interesting contrast was the Valiant 40 compared the to Esprit 37. Both canoe sterned, skeg hung rudder boats that were close to identical in the geometry of the rudder, skeg and prop. The Valiant 40 has no noticable prop walk at all while the Esprit had some. Not much but enough to get your attention in the marina. I wish I had an answer.
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