The wheel effect

How the propeller pushes the stern sideways (exam term D.1).

What is it?

The propeller doesn't only push forward or backward; it also pushes the stern sideways. The spinning screw acts like a wheel pressing on the water: the lower blades turn in deeper, denser water (more grip) than the upper ones, and that difference creates a sideways force on the stern.

Try it yourself

push on the stern bow swings along

Right-hand screw, reverse → the stern goes to port (left) — strong, clearly felt.

Bank effect (bank suction)

Too fast close to the bank in shallow, narrow water? The stern is sucked in and the bow pushed off — the bow sheers to port. Drag the speed to see the effect grow.

Speed

slowtoo fast

The bow sheers to port (away from the bank).

Skipper

The skipper's tip

Remember just one case — right-hand screw, reverse → stern to port. You can derive all the rest: forward is the opposite and weaker, and a left-hand screw is the mirror image.

Skipper

And when berthing

With a right-hand screw, pick a berth on the port side. A short burst of reverse to brake near the quay swings the stern towards the wall.

The direction (right-hand screw = standard)

	Stern to	Bow to	Strength
Forward	starboard	port	weak
Reverse	port	starboard	strong

With a left-hand screw everything is mirrored. Memory aid: right-hand screw + reverse → stern to port (left).

Turning: wide vs. narrow fairway

In wide water you simply make a wide turn. In narrow water you turn 'in a tight spot' using the wheel effect: a right-hand screw turns most easily to starboard, a left-hand screw to port. Pick the propeller and the fairway.

Propeller

Fairway

right-hand screw — This screw turns most easily to starboard.

In a narrow fairway you turn 'in a tight spot' with short bursts of forward and reverse. Because you now have to go astern, you turn the opposite way to wide water — to starboard — since in reverse the wheel effect pulls the stern to port.

Go slow; put the rudder hard to starboard. The bow starts to swing to starboard.
Give a short reverse. The wheel effect pulls the stern to port, so the bow swings further to starboard (= turning to starboard).
Go briefly forward again with the rudder to starboard. The bow swings further still.
Repeat forward/reverse until you have turned 180° — almost on the spot.

Why stronger in reverse?

The propeller is built to push forward; then it cuts cleanly through the water and the side effect is small. In reverse it works much more turbulently — that's when you clearly feel the wheel effect.

What do you use it for?

Mooring: with a right-hand screw you berth more easily on the port side. A short burst of reverse to brake near the quay pulls the stern towards the wall.
Turning in a tight spot: combine a short forward (rudder hard over) with a short reverse (the wheel effect pulls the stern along) to turn almost on the spot.
Leaving: you can push the stern off the quay by cleverly choosing forward/reverse.