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  #1  
Old 03-30-2013
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Minimizing prop walk...

Full keel boats have their advantages.... and parking in tight places ain't one of them! My boat LOVES to prop walk (to starboard) in a big way. My usual procedure is to back up with the engine at low rpm and rudder hard to port, and begin swearing promptly when the stern goes to starboard as it always does.

Is there an accepted way to minimize prop walk? Would I have less walk if I used quick bursts of throttle in reverse instead of a steady low/med rpm? Is there something else (besides a bow thruster) that I should be doing different?

Backing out of my slip is always the part of the voyage that I worry about, and dread the most.

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Re: Minimizing prop walk...

Quick burst of high revs will minimize prop walk until you get some steerage. You could also look at a feathering prop. Most of the feathering props will generate a fraction of the walk that a fixed prop will.
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Old 03-30-2013
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Re: Minimizing prop walk...

Less rudder, small bursts of throttle the get things going followed by waiting a moment in neutral to see wheich way she is going.
Your biggest enemy is going to full rudder, it seems to block part of the water flow to the wheel (storry old tug boater term) which causes negative pressure on one side of the boat.

from Wilkipedia

Propeller walk is the term for a propeller's tendency to rotate a boat as well as accelerating it forwards or backwards.

A right-handed propeller (which rotates clockwise [as viewed from the stern] when in forward gear) will tend to push the stern of the boat to starboard, thereby pushing the bow to port and turning the boat counter-clockwise unless the rotation is corrected for.. When in reverse gear, the effect will be much greater and opposite. A right-handed propeller run in reverse will push the aft of the boat to port.

Knowing of and understanding propeller walk is important when maneuvering in small spaces. It can be used to one's advantage while mooring off, or it can complicate a maneuver if the effect works against the pilot.

Propeller walk is a complicated effect which depends on ship geometry, direction of travel, propeller direction, vessel speed and depth of water. Three causes are identified for a vessel in deep water:-

Upward oblique flow at the propeller location.
Vertical wake distribution at the propeller.
Unbalanced lateral forces on the rudder (when set amidships) arising from the propeller slipstream impinging on the rudder blade.
The first of these results from there being a measurable difference in speed of water flowing close to the hull and that at lower depths which has not been affected by the vessel's motion. At low speeds the last effect is most pronounced and when going astern has even more influence.

In shallow water the upwards flow from under the vessel becomes much less strong and ultimately disappears. Model tests carried out show that, at a very small underkeel clearance, screw bias caused a ship to shear to starboard (rather than port) when moving ahead and that there is an intermediate depth where the shear from bias is neither one thing nor the other.

Finally, when moving ahead with the propeller moving astern, flow into and around the propeller is very confused. Generally the overall result for a single screw ship when stopping is a shear to starboard, but this is not always guaranteed; sometimes it may go the other way, depending often on any yaw rate on the vessel when the propeller starts to turn astern.

sounds like a simple answer, you need a sli[p with an adjustable depth
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Old 03-30-2013
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Re: Minimizing prop walk...

To decrease prop walk sail drives might be an option. The prop is close to the center of the boat and the prop walk tries to "walk" the whole boat to one side instead of pushing the boat from a long distance from the center.
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Old 03-30-2013
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Re: Minimizing prop walk...

I don't know it would work on a boat as heavy as yours but on some boats I have been able to counter act the prop walk by having a crew member shove the stern hard the opposite the stern will move once the prop walk starts.
That give you another second to two of stern-way before you have throttle back.

As an alternative a loose stretchy stern line looped over the cleat.
You start in reverse and when the stern line fetches up the stretch gives your boat a little way to counteract the prop walk then at the right moment you flip off the stern line.

In both cases the attempt it to over correct for the prop-walk with lateral force to give you a couple more seconds going mostly backwards.
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Re: Minimizing prop walk...

Quote:
Originally Posted by MedSailor View Post
Full keel boats have their advantages.... and parking in tight places ain't one of them! My boat LOVES to prop walk (to starboard) in a big way. My usual procedure is to back up with the engine at low rpm and rudder hard to port, and begin swearing promptly when the stern goes to starboard as it always does.

Is there an accepted way to minimize prop walk? Would I have less walk if I used quick bursts of throttle in reverse instead of a steady low/med rpm? Is there something else (besides a bow thruster) that I should be doing different?

Backing out of my slip is always the part of the voyage that I worry about, and dread the most.

MedSailor
Every boat has it's quirks..

I have found that the best way to sort them out with a new boat (or testing new techniques) is to locate some empty mooring bouys to use for testing - not so hard if you miss

Some things to try.
  1. More speed going aft (I know it feels frightening)
  2. Turn to starboard before going aft countering the prop walk after engaging revers (assuming you get steering going aft with increased speed se 1)
  3. When going aft keep the rudder to port, it wont be able to counteract the propwalk anyway), use bursts of forward to move the stern back in line
  4. Test the other suggestions in this thread
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Old 03-30-2013
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Re: Minimizing prop walk...

Med- our boat isn't full keel, but a long fin and large skeg hung rudder with a three blade fixed prop. It turns to port in reverse, a lot. I've found that putting the rudder just a bit to starboard and an initial blast of throttle until the boat is moving at least a knot or better and then shift to neutral is the best that can be done to try and back out reasonably straight. If I just let the engine idle in reverse I would hit the boat to port and the bow would scrape along the finger pier. If I have crew I will have them walk along trying to hold the starboard bow off until they have to climb aboard. I really wish I had a port tie slip because coming back in is not much better :-(( I think a Max Prop is in my future (when I save up 4K).
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Re: Minimizing prop walk...

Thanks for the suggestions so far. One thing I haven't tried is anything less than full port rudder when I really want to counteract the starboard walk in reverse. I could try a little less.

I have used bursts of forward to good effect to get her back in line, but then again we often end up loosing our sternway.

I don't have the coin for a feathering prop, though I covet them. This week we're going in the yard and I'm adding an inch of pitch back to the prop. It seems to me that this problem magnified significantly when I took 3 inches of prop out.

As for the slip, I need to experiment with lines to help. I do own the slip and can modify it, so I should take advantage of that. I've been meaning to try something I saw in "Good Old Boat" whereby you run a taught line or wire along your finger peer. You then have a short line with a sliced eye that slides along the wire as you back up. You can pull on the line while you're backing up and it will always be perpendicular to the slip.

MedSailor
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Re: Minimizing prop walk...

Don't know if it will work for your boat, but I've found that giving the engine a rev in reverse to get the boat moving and then putting it in neutral will usually allow me to steer while moving backwards. Once the engine is in neutral the prop walk stops and if you've got steerage the rudder should control things.
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Re: Minimizing prop walk...

Quote:
Originally Posted by billyruffn View Post
Don't know if it will work for your boat, but I've found that giving the engine a rev in reverse to get the boat moving and then putting it in neutral will usually allow me to steer while moving backwards. Once the engine is in neutral the prop walk stops and if you've got steerage the rudder should control things.
This is what I do as well (I probably wasn't clear about that) but what I think I need to experiment with next is how to get that initial steerageway. I've been using low/med rpm to get that initial steerageway but I think today I'll try more of a burst.

Agreed +1 about putting the engine in neutral once we're going backwards a little. Usually by then, I'm crooked in the slip and my bowsprit is about to snuggle up with a piling.

MedSailor
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