The wheel effect refers to the lateral displacement of the stern in motor-powered vessels.
The wheel effect occurs primarily when travelling astern, and particularly with rigid shaft propulsion. When travelling forwards, the rudder effect is much less noticeable. It is also significantly less pronounced in propulsion systems where, unlike in rigid shaft propulsion, the propeller is not located directly beneath the hull.
The direction in which the stern is displaced by the rudder effect depends on the direction of rotation of the propeller. It is therefore helpful to know the propeller’s direction of rotation when manoeuvring.
When mooring, the wheel effect can be extremely useful, as it pulls the stern of the boat towards the jetty. Of course, other factors such as wind, current and space constraints in the harbour must also be taken into account for a successful mooring manoeuvre – which is why, in reality, it is sometimes not possible to moor on the ‘optimal’ side.
This example assumes a right-hand-rotating propeller. When the throttle is open (forward), the right-hand-rotating propeller rotates clockwise when viewed from behind.
This example assumes a right-hand-rotating propeller. When the throttle is open (forward), the right-hand-rotating propeller rotates clockwise when viewed from behind.
A spiral-shaped flow towards the bow
The wake effect is particularly significant when the engine is in reverse:
When the engine is in reverse, the rotation of the propeller creates a spiral flow towards the bow (forwards). This spiral flow does not flow past the rudder blade.
The spiral flow ‘bounces’ off the side of the vessel and pushes the stern towards the other side.
The spiral-shaped flow pushes the stern to one side
Direction of rotation of the propeller as seen from astern (= from the rear):
When reversing, the wheel effect causes the stern to veer to port.
A clockwise-rotating propeller turns anti-clockwise when travelling in reverse. The wheel effect creates a spiral-shaped propeller wake towards the bow.
The propeller wash ‘strikes’ the starboard side of the ship and pushes the stern to port.
Viewed from astern (= the rear), a right-hand-rotating propeller turns clockwise when the vessel is travelling forwards.
When travelling in reverse, the stern is shifted to port by the wheel effect in the case of a right-hand-rotating propeller (which rotates anti-clockwise when travelling in reverse).
With a clockwise-rotating propeller, the port side is recommended as the mooring side, as the wake effect pulls the vessel towards the pier.
Direction of rotation of the propeller, viewed from astern (= from the rear):
When reversing, the wheel effect causes the stern to veer to starboard
A counter-rotating propeller turns clockwise when travelling in reverse. The wheel effect creates a spiral-shaped propeller wake towards the bow.
The propeller wash ‘strikes’ the port side of the ship and pushes the stern to starboard.
Viewed from astern (= the rear), a left-hand-rotating propeller turns anti-clockwise when travelling forwards.
When travelling in reverse, the stern is pushed to starboard by the wheel effect in the case of a left-hand-rotating propeller (which rotates to the right when travelling in reverse).
With a counter-clockwise-rotating propeller, the starboard side is recommended as the mooring side, because the wake effect pulls the vessel towards the pier as it brakes (the propeller rotates in reverse during braking).
The rudder effect is not only helpful when mooring, but also during the ‘turning in a tight space’ manoeuvre with a rigid shaft.
During the ‘turning in a tight space’ manoeuvre, the boat is turned as if on a ‘turntable’.
With a rigid shaft drive, there is no need to turn the rudder back and forth: the rudder remains turned in the same direction throughout the entire manoeuvre.
With a right-hand propeller, turning is achieved via the starboard side with a full turn to starboard, whilst with a left-hand propeller, turning is achieved via the port side with a full turn to port.
When shifting into reverse, the motorboat is brought to a halt from its initial forward motion, whilst the wheel effect additionally shifts the stern of the boat. The wheel effect thus aids a quicker turn.
Initial condition: Engine idling, vessel stationary
Full turn of the rudder to starboard
Forward thrust to initiate the rotational movement
Disengage the clutch as soon as the boat starts moving forwards
Reverse thrust to stop the boat’s forward motion and, through the wheel effect, enhance the turn
Disengage the clutch as soon as the boat starts moving backwards
Forward thrust to stop the boat from moving backwards and to enhance the turning manoeuvre (caused by the flow around the rudder, which has been turned to starboard)
Disengage the clutch as soon as the boat starts moving forwards
Align the oar blade straight
Stop it correctly in line with the thread (for a left-hand screw)
Error when stopping in line with the course (for a left-hand propeller)
The wheel effect is not always an advantage when manoeuvring. In some situations, the wheel effect is a hindrance and requires deliberate countersteering, for example when ‘stopping whilst maintaining course’.
To bring a motorboat travelling forwards to a halt, you must apply reverse throttle to slow the boat down. The reverse throttle creates a wheel effect, which imparts angular momentum to the stern of the boat. To stop whilst maintaining your course, you must turn the rudder during the braking manoeuvre:
When the engine is in reverse, the rudder is no longer exposed to the propeller wash but continues to be affected by the water through which the vessel is travelling, as long as the braking manoeuvre is not complete. The rudder, which has been turned to one side (known as ‘counter-rudder’), counteracts the wheel effect.
If the ‘stopping on course’ manoeuvre is successful, the boat is shifted slightly to one side, but the bow continues to point in the same direction.