Prop walk is an interesting marine phenomenon that occurs when a yacht or boat’s propeller generates a sideways force or movement as it is drives forward or backwards. This lateral movement can make it challenging for boat operators when they try and manoeuvre their vessels, especially at low speed or when docking.
It is usually associated with boats that use a single screw propeller and the magnitude of the effect can vary depending on several factors, including the design of the boat, the type and size of the prop, and the engine’s power.
Some key points about prop walk include:
- Direction: When your propeller spins in gear, it produces thrust that drives the boat forward. However, props are far from 100% efficient, so some of that forward thrust will also be converted to a sideways force.At high revolutions per minute (RPM), the ratio of the forward thrust to the sideways force is overwhelming, and prop walk becomes negligible. But when a boat’s speed is close to idle, the forward thrust is less pronounced, and prop walk will visibly swing the stern.Prop walk can occur in either a port or starboard direction, depending on the specific boat and propeller design. When a boat is put into gear (forward or reverse), it may move to one side rather than going straight.A single right-handed fixed propeller will tend to push the stern of a vessel to starboard when going forward and to port when going in reverse.
- Causes of Prop walk: Prop walk is primarily caused by the way water flows over the blades of the propeller. As the propeller rotates, it creates a flow of water, and this flow can exert a sideways force on the stern of the boat, causing it to move to one side.The sideways force can be further exacerbated if the prop is not parallel to the water’s surface. In fact, most sailboat shaft angles will be between 8 and 14 degrees and therefore the thick twist of the blades act like a paddlewheel, creating a sideways thrust away from the spin direction.If you want to see this effect on your own boat, find an open water spot on a calm day. Drop your boat into reverse and leave it to idle in the water with the rudder centred. Now wait. Almost all boats will walk. At the extreme level, a boat will spin full circle if you let it.
- Resistance to Steering: Prop walk can create resistance to turning the boat’s wheel or tiller. When trying to make a turn while at low speeds, you may feel the boat resisting your efforts to steer in the desired direction. This can make turning and manoeuvring more challenging.
- Sensation of Drag: Some boat operators describe prop walk as a feeling of drag or resistance on one side of the boat, which can make it feel sluggish or less responsive to steering inputs.
- Effect on Manoeuvring: Prop walk can be used to your advantage when manoeuvring your boat. However, for inexperienced operators, prop walk can be challenging to control and may lead to difficulties in docking or navigating in close quarters.Skilled operators learn to anticipate and harness prop walk to assist in making tight turns or docking in specific situations. For example, when doing low-speed manoeuvring coming into dock, your prop walk can act almost like a low power stern thruster.
Tips for using Prop Walk for close quarter manoeuvring
- Use Short Bursts of Power: When manoeuvring in tight spaces, use short bursts of power rather than prolonged, continuous throttle. This method gives you better control over the boat’s movement and allows you to make adjustments more easily.
- Practice in an Open Area: If you’re new to a boat with prop walk or need to build up some confidence in handling, practice in a safe, open space. Try using different throttle settings and steering inputs to see how your boat responds.
- Experiment with Propeller Settings: Experiment with different propeller settings to see if adjusting the pitch or angle can help mitigate the effects.
- Use Bow Thrusters: Some boats are equipped with bow thrusters, which are small, sideways-facing propellers at the front of the boat. These can be used to counteract the lateral force of prop walk and make manoeuvring easier.
- Learn to “Walk” the Boat: A skilled boat operator can use prop walk to their advantage by using it to pivot the boat in tight spots. To do this, engage forward or reverse power and then shift into neutral while using bursts of throttle to control the direction and degree of turn.
- Practice Docking: Propeller walk is often most noticeable and challenging when you are trying to dock. Practice docking in various conditions and at different docks to become proficient. Don’t forget to use fenders and lines to protect your boat and minimise any damage when you are practicing.
It is important for boat operators to understand how prop walk can affect the manoeuvrability of a boat. However, with a bit of practice, you will become more confident in your ability to handle your boat in various situations, including tight manoeuvres and docking.