How do I overcome prop walk?
Dear Boat Doctor,
I have a 1974 Cal T2-27 with a Yanmar 1GM10. My prop is a twin-blade 12RH10 and my prop walk to port when in reverse is pretty significant. My slip situation calls for backing out to starboard and when the prevailing breeze is up, it can get pretty challenging. I like my slip and I would like to stay bow forward. I can often finesse it out by alternating powering up to get steerage and gliding, but it doesn’t always work well. I sometimes end up having to go with the port side turn and back down the channel to get out of the marina, which is not difficult but not preferable.
Moss Beach, California
Prop walk can be frustrating, but at times useful. Prop walk in the proper direction can help you control your boat, but in the wrong direction it can cause you to spin out of control. Prop walk occurs when the paddlewheel effect of the prop overcomes the forward or reverse thrust and, most importantly, the water flow over the rudder. It occurs in forward or reverse, but it is more noticeable in reverse. In forward, the thrust of the prop is greater and water flows more quickly over the rudder giving steerage.
The key to backing up straight or turning against prop walk is to get way on gradually to get water flow over the rudder. You may be tempted to hit reverse hard and then back off, but that initial burst of power will pull the stern over to port. A better solution is back out with a little power and increase it as you get moving. Keep the rudder straight until you get way on, otherwise it will just stall and slow the boat down. As the boat speeds up, turn the rudder against the walk.
You may need to resort to an aft-turning spring line when the wind or current pipes up. Rig a doubled spring line that is about twice as long as your boat from your starboard stern cleat to your dock. As you back out, use the line to keep the stern close to the dock, and then pay out line you back up. When the bow is about to clear the slip, snub the spring and your bow will pivot off to port. When the boat has turned enough, drop the spring and quickly retrieve it, being careful to keep it out of the prop.
At times a good dose of prop walk can be your friend. You can also borrow a technique called back-and-fill from the powerboat world. To rotate your boat in a tight clockwise circle from a stop, set the rudder to turn to the right and leave it there. Next, give a short burst of forward power to push the stern to port, shift to neutral and give a short burst of reverse to walk the stern to port, repeat. Alternating between forward and reverse will keep the boat in one place but will rotate it in place.
Bob Pingel, a Coast Guard-licensed captain, runs Custom Line Splicing LLC. Send your questions to the Boat Doctor, SAILING Magazine, P.O. Box 249, Port Washington, WI 53074, or send email to firstname.lastname@example.org.