Doin' Da prop walk Boogie

[Wahoo Sails]

Our "new to us" Nomade has a 2 bladed prop, and prop walks worse than anything I've ever been on. Obviously, a 3 bladed prop will help the sutuation, but in the meantime are there any techniques to help minimize the situation?

L S/V Love Nest
Bob & Lynn

[GordMay]

Boat Handling advice: http://cruisersforum.com/showthread....&threadid=1462

[Alan Wheeler]

It's not so much the number of blades, but the surface area and pitch that causes the prop walk. In other words, the amount of rotational friction the prop has in the water. This can be improved with Propellor design. However, the most important thing you can do, is ensure you have the correct size and pitch to match your boat. Oh and boat hull can an an effect. If it has little lateral resistance at the point that effort placed on the hull, it will cause the hull to pivot easier than a design that has greater lateral resistance at that point. ie. large rudder/keel.

[GordMay]

What Wheels said, and the basic standards for prop’ and pitch could be stated:
Slow Displacement Hulls (Sailboats): Bigger Diameter, Less Pitch = Power
Fast Planing Hulls: More Pitch, Smaller Diameter = Speed

[BC Mike]

I keep hearing about this prop walk thing and feel like I am missing something. Why don't I get it. I bung it in reverse and give it some throttle and we go backwards. The steering is no good until we hit about two knots and then everything is fine. If you do not give it enough throttle to get the required speed then the steering will be no good. I have been backing out of my stall for a long time in all conditions and it works every time. What am I doing wrong?
Michael

[Wahoo Sails]

Thanks guys!
Gordy, you bet prop walk can be a good thing! When we went to leave the dock she was tied to, I used it to good advantage, she was in a 50' wide canal (36' boat) and the prop walk turned us so smartly that friends aboard accused me of having practiced the night before
Wheels, Hull design you say? This is s swing keel boat, and we had her cranked all the way up (wind had driven the water out of the river we were in) ... duh ... ya think that could have anything to do with it?
BC Mike, Count yer blessings! Have never yet ben aboard a sailboat that backed down "nicely" ... but this one really takes the cake ... put her in reverse & for every foot that you go astern, you go 3 to port!
As for planning to depart before you tie up ... that's why we tie stern into our slip ... departure is a piece of cake that way. Once knew a guy that used to hang a trolling motor over the port stern quarter to counteract the effect of prop walk ... not ready to go to that extreme ... but I sure understand why he did it

L S/V Love Nest
Bob & Lynn

[Alan Wheeler]

Don't worry ya self Mike. I don't get any prop walk either. But then the boat is 26T, 46ft, and has a 7ft draft with full keel and a barn door for a rudder. As for steering in reverse, or I should say lack of it. Firstly, a Propellor is working in two ways. One, it is "propelling" itself through the water. The thrust is transfered via the shaft and to the hull and pushes it through the water. But a second energy source is the water moving away from the boat. This movment of water is used to move the boat in a different way. When in forward, the prop is delivering a fast moving volume of water over/around and past your rudder. When you turn the rudder, you deflect/direct this flow of water. The water pushing against one side of the rudder causes causes a high pressure side and the otherside is low pressure, thus the rudder moves to the low pressure. The Rudder being attached to the boat drags the hull along with it. This very reason of rudder being virtually sucked to the direction of low pressure and thus dragging the rear of the vessel around, is why the boat pivots around a point further along her hull. But thats a side track.
When the propeller is in reverse, the flow of water is no longer around the rudder. So the only time the rudder will have any influence on direction, is when the water is moving fast enough for a sufficient force to be formed against the rudder. This is why a vessel moving in reverse pivots at a different point than when it was moving forward.
You also have to be careful of vessels with very large barn door type rudders. The force exerted against a rudder when reversing is huge and very different than the propeller wash. It does require some speed, but the rudder or/and it's steering components can in fact be damaged in extreme situations.

[David W]

to figure out how much throttle in reverse would get me moving backwards enough to get steerage so I could use the rudder to counter steer. That said once I have enough momentum, I put her in neutral, steer and use occasional shots of reverse if I slow down too much.

I have a 34 ft tiller steered boat and I stand facing aft when backing to make sure I point the tiller the right way... there's enough going on without adding tiller direction confusion to the mix!

Cheers
David

[harryrezz]

Dave W made a very important point. You'll only experience than pull to port when the prop is turning fast enough to be "pulling" the boat backwards. As soon as you cut the throttle or shift into neutral the effect will stop and you can steer ... more or less, depending on other characteristics of your boat. So the key is to gun the throttle anough to get the boat moving sufficiently to generate a water flow past the rudder. Then cut her back and steer, giving occasional bursts of throttle as needed.
Another hint - if you plan ahead you can use that "walk" to you advantage sometimes. When docking go in portside to the dock when possible, and approach at a small angle. then, just as you reach the point where you want to stop, pop her into reverse and give her a good burst of power. This will stop the boat and the "walk" will pull the stern along side very nicely. Takes a little practice, but you can look like a real pro in no time.
The reverse can also sometimes be used. When leaving a dock when you are starboard to, leave in reverse and the "walk" will pull the stern away from the dock for you allowing you a nice, clean exit.
Of course, don't forget thefenders!