Prop Walk

[SFS]

My '83 H31 has what I consider a fair amount of prop walk to port in reverse. One thing that has helped me a great deal is something I saw in a video. When backing, I deliberately separate throttle changes from steering changes. Starting with neutral helm, I get the boat moving backward with a dose of RPM, return to idle (remaining in reverse), and only then apply some helm in the appropriate direction. If rate of turn is not enough, and I'm certain the boat is moving enough for the rudder to be effective, I add some more rudder. If the problem is lack of speed, I surge the RPM very briefly and come back to idle. I avoid changing helm inputs and RPMs at the same time. This approach keeps me focused on the variable I am changing at any given instant.

Until you know just how much throttle it takes to get the boat moving, and become familiar with how much helm it takes to move the stern by a certain amount at a given speed, it will be easy to fall into a cycle where all your control inputs become unproductive, or even counterproductive. This cycle can be entered at any point, but often starts with a shortage of way, followed by putting the rudder over farther than necessary in an attempt to compensate. The rudder can then become more of a brake in the water than a steering device. Subsequent throttle increases then SEEM necessary, but are MUCH less effective, so more helm is added, and so on.

Edit: I just reread your original post, and two things stand out. One, after your burst of throttle, just go to idle, but remain in reverse. This will help at least a little in maintaining steerage. It may also let you back at a slower speed, curing the second item - the feeling of running out of room too quickly. Good luck.

 

[Jim Legere]

All good info here, although I had never heard that sail drives don't have prop walk (still trying to get my head around that). Unless you re-power with something that has a left-hand prop, your are stuck with your H37 Cutter walking to port in reverse. The key is to try and make that work for you. The suggeston to back in your slip is a good example. When you learn to make prop walk your friend, you can do some pretty cool things. On a calm day, in a place with lots of room and no current, try playing with different throttle, rudder and boat speed combinations. Its neat what can (and can't) be done. Don't ever let go of the wheel in reverse though; on our boats you will bang the rudder stops pretty damn hard!

 

[braol]

as far as the 20hp thing way before axillary power they sailed in an out of slips and morings ...

Remember though that lots of boats back in the day had extra crew and either rowed or warped themselves in, especially larger ships.
I sailed into my mooring one time...wind was perfect and I was running in under a loose jib all set to fall. The power boaters around me were at the same time both appalled and fascinated. I don't make a habit of it, but if the wind is right it can be a very satisfying maneuver...and stress free (with the motor at idle and ready to go of course). Extra fenders all around doesn't hurt either. In fact, extra fenders and a nice pole to help fend you off are a good idea anytime.
The fact that you have a 37-footer I'm sure only adds to the stress of coming in/going out. That's a lot more boat to get moving than, say, my H27. I agree with the others in that experience is the best teacher...heck, go to the marina on a Tuesday morning when no one is around and just practice pulling in and out a few times. Like many others you can experiment with lengths of rope attached at various points that you can access quickly to get yourself attached. I find the most valuable line is a real long rope attached to a forward cleat on the boat that runs all the way to the cockpit. When you get close you can either toss the middle of the line to a dock cleat or post and then tie the end off at the back...or do the "Leap of Faith" onto the dock with line in-hand and secure. I find that if I put the boat into idle reverse just as I touch the dock (dock on port side) and secure the front of the boat, that the aft end of the boat will 'prop walk' and take up slack on that fore end rope and the boat just pivots into the dock and holds itself there. This can be valuable especially if the wind is trying to push you AWAY from the pier and into your neighbor.

 

[JohnVTX]

All good info here, although I had never heard that sail drives don't have prop walk (still trying to get my head around that).

Why a Sail drive boat does not walk..... Case 1 is sail drive. Case 2 is shaft drive
Prop Walk. An explanation of its causes and effect. Prop walk is also known as, asymmetric blade effect, asymmetric thrust and P-effect. It affects boats, propeller driven aircraft and helicopters. Here we consider the effect on boats. This paper explains how the propeller shaft angle (the angle between the surface of the water and the shaft) causes the thrust of the up-going and down-going blades to differ, so producing prop walk. The example uses a two bladed propeller; this is for ease of explanation only, the number of blades makes no difference to the effect. Case 1. A propeller with no shaft angle. Consider below, a right-handed propeller, in reverse. The propeller blades are scribing the red and blue lines on a cylinder of water. This shows the paths of the red up-going and blue down-going blades during the rotation of the propeller. The schematic below shows the cylindrical paths of the blades as a flat representation during one rotation. As can been seen the red and blue paths are of the same length, the blades travel the same distance, therefore the thrust from the up and down blades of the propeller is equal. Red up-going path, starboard side Blue down-going path, port side Right hand propeller in reverse. Boat with a horizontal shaft, in reverse. Blue down-going path, port side Red up-going path, starboard side The thrust from the port and starboard sides is equal and in line with the propeller shaft; there is no prop walk. Blue down-going path, port side Red up-going path, starboard side As can been seen the red paths are longer than the blue. This means that the up-going blade on the starboard side travels further than the down-going blade on the port side, This up-going blade travelling further pushes more water towards the bow of the boat, producing more thrust. The schematic below shows the cylindrical paths of the blades as a flat representation during one rotation. Case 2. A propeller with a shaft angle. This propeller and shaft have a shaft angle to the water surface. As in Case 1, the propeller blades scribe the red and blue lines on the surface of a cylinder. The lines show the different paths of the up-going and down-going blades. Prop walk is caused by the angle of the propeller shaft to the water surface; if there is no angle, then there is no prop walk. For an increase in either the diameter or pitch of the propeller the effect is increased. The effect is present in both forward and reverse gears. In forward gear the forces act to yaw the boat to starboard. In forward gear the effect is easily overcome by the rudder. In reverse gear the rudder is less effective making prop walk more obvious and difficult to control.

 

[Jim Legere]

John,
What you say is true for the asymmetric blade effect, which is a component of prop walk. Other components of prop walk are paddle wheel effect (at slow shaft speed) and prop to hull to rudder geometry, which varies from design to design. I believe that a sail drive has very little prop walk when compared to a conventional shaft design, but I suspect only concentric, counter-rotating props, such as the Volvo Duoprop, totally eliminate prop walk. Interesting thread; some great information here.

 

[Dennis Kitchen]

JohnVTX and Jim Legere explain the causes of prop walk very well. An additional observation I've made about sail drives is they are mounted considerably more forward on the boat, closer to the center of lateral resistance, thereby reducing the "arm" of the turning effect. If any prop walk remains it will likely be indicated by slow sideslip rather than turning; as compared to a boat with stern drive.

 

[jssailem]

Rob. It is all about practice. Get out of the marina. Find a spot where you have some space. And just drive the boat around. Forward and backward straight lines. Left and right circles forward and backwards. Think like you are 16 again and you want to drive a car. Where were you allowed to go? A big empty parking lot.

Anchor a buoy and try to approach it like you were docking. Approach going forwards and backwards ( this is also a great way to practice MOB recovery). With a little time you and the boat will start to understand each other and you'll be an old salt at finding and securing the boat in the slip.

 

[jssailem]

Oh and if the CG comes by and wants to know if you've been drinking. Nah just learning to drive. That will come later.

 

[Kings Gambit]

You make managing prop-walk sound like one needs the skill and practice of a tight-rope walker just to back of a slip. It's just not that big of a deal.

 

[bshock]

You make managing prop-walk sound like one needs the skill and practice of a tight-rope walker just to back of a slip. It's just not that big of a deal.

Finding a comfort level very much is a big deal, particularly when you're maneuvering a 7+ton boat in a close-quarters situation with other expensive boats around you. When I went from a 25 foot sailboat to the 36, it was like a completely different animal, and I had some anxiety leaving from and returning to the dock. But after taking two paid lessons on close-quarters maneuvering, and just practice practice practice, I learned how my boat behaves (mostly) and how to control it (mostly). I'm still learning, but I feel much more comfortable leaving from and returning to the dock.

 

[braol]

I learned how my boat behaves (mostly) and how to control it (mostly).

Mostly, the most applicable word in sailing!

 

[tango_51]

LOL welcome to the club... you have to get water moving over the rudder while maneuvering aft before the boat will respond.. sucks I know but once you get some momentum they easy to maneuver.. just try not to bang the boat up to much while getting out of the slip... take your time and use the wind if its in your favor.