Prop Wash vs. Prop Walk
Imagine yourself on vacation somewhere nice in the islands. You got a perfect breeze, lots of sun, and the day is coming to an end. It's time to pull into a slip at a marina and the harbormaster says you need to back in between two boats. No problem right? You line up the boat and put her in reverse. Slowly backing up, you notice that the stern is turning hard port, causing you to completely miss your slip. If you don't do something you will hit the 50 ft oyster yacht next to you. Quickly, you put the boat in forewords. The water is rushing out the back and the bow turns hard starboard! Oh no! What is going on?
Answer: You are experiencing prop walk and prop wash. Sailboats move by the water flowing down under the boat and over the rudder, which gives you the ability to steer the boat in the direction you need. When a motor gets into gear, the flow over the rudder changes and the boat is prone to react on its own, instability we call prop walk and prop wash. With a little understanding, you can predict it before you find yourself cozying up to a thousand dollar nightmare.
So what is prop walk? Prop walk is when the boat rotates when you put it in reverse with little to no steerage on the helm aka seemingly by itself. If you have a right-handed prop (prop spins clockwise in forewords), then when you are in reverse, the prop spins counterclockwise. This sudden change in rotation on the prop causes the stern of the boat to dramatically walk to the port - spins left, walks left. Prop walk occurs most frequently in reverse. You will have to be in motion for steerage to return to the wheel enough to navigate without prop walk taking you for a stroll.
Prop wash happens when changing from reverse to forwards or if you suddenly accelerate from a dead stop. These sudden movements cause the prop's spin to create turbulence over the rudder, causing instability while steering. If you have the wheel turned to the right a little bit, this will make the boat turn sharper to starboard then expected until it gains speed. If you arrive at speed gradually, your steerage scope will be returned. Some sailboats experience these effects worse than others due to the vessel's shape and where the prop is located.
Prop walk and prop wash aren't necessarily bad - they can be used to your advantage in tight docking situations. For example, if you approach the slip from an angle the boat can walk right into the slip. Parallel parking for the pros. Not only do you look like a rock star, you also work smarter, not harder. Avoid stressful situations docking (and with their expensive boats!) and use the concepts of prop walk and prop wash to your advantage next time you dock!
Cameron Sarik, Northern Virginia Sailing School