Understanding prop walk, or how to use the direction the propeller is turning, will help you control your single-screw boat in low-speed and docking situations. Here’s a great primer from iNavX that tells how to do it:
When your propeller spins in gear, it produces thrust that drives your boat forward. Indeed, most of the force of the propeller contributes to the direction of motion. But not all of it.
A propeller is far from 100% efficient, and a simple unidirectional propeller pushes water in multiple directions. The primary direction of thrust is aft when the transmission is in forward of, and forward when the boat is in reverse. But there is also an element of side thrust, akin to what a paddle-wheel produces. And this causes the propeller to “walk” to one side of the other.
At high revolutions per minute, the ratio of forward thrust to the side force is overwhelming, and prop walk becomes negligible. But at speeds close to idle, the forward thrust is less pronounced, and prop walk will visibly swing the stern. And you can use this.
Right and Left Handed
To envision how your prop walk develops, picture your propeller spinning at low speed. Viewed from the stern, a right-handed propeller rotates clockwise to go forward. Now, swing your view around to the side of the boat and look at that propeller. It’s not flat, not even close to it – propellers are pitched screws, and they’re always several inches deep.
That thick twist of the blades acts like a paddlewheel, creating a sideways thrust away from the spin direction. So a right-handed propeller in forward gear will push the stern of the boat to starboard. In reverse, it will push it to port.
More Walk in Reverse
Propellers are optimized for forward motion, and for most of us, that means our boats back much more slowly than they go forward. This also means that in reverse gear, prop walk is stronger because the propeller pitch is so much more inefficient.
If you want to see the effect on your own boat, just go to some open water on a flat day. Pop your boat into reverse and leave it in idle with the rudder centered.
Using your prop walk
For low-speed maneuvering, your prop walk is almost like a low power stern thruster if you work it right. It can help you with several tight maneuvers and make you look like a pro in close quarters.
These techniques don’t work at high speeds, you need to let the walk do the work.
Cautions:
- Go EASY on the throttle. Do most of this at idle.
- Always pause between forward and reverse to let the transmission stop spinning every time. Do NOT slam it back and forth without pause or you may damage your transmission.
- Keep a sharp eye on your overhangs. You don’t want to clip your davits or anchor on something!
- Don’t forget about wind and current, both can make these maneuvers more difficult. Read more: https://inavx.com/2023/05/05/prop-walk-your-low-speed-friend%EF%BB%BF
