Wheel fenders have a sliding axle and rollers to increase deflection and energy, so are suitable for
lock entrances and vulnerable berth corners. Roller fenders have a fixed axle to allow almost zero resistance rotation, suitable for guiding ships within locks and dry docks.

During lock and dry dock approach the ship is nearly parallel to the lock wall, but can be closer to one side. The bow contacts the wheel fender which deflects the ship. As the ship continues to enter, the roller fenders act as a guide to protect the hull and lock wall.

Some conventional berths have exposed corners which need protection from a wheel fender. Although the ship can be at a large angle to the main fenders, the effective berthing line on the wheel fender remains at 0°. In many cases mid ships impact should be considered.

SPECIAL IMPACT CASE

If the ship is moving into the lock or dry dock then impact with wheel fender can occur on the bow section. The effective berthing line is the tangent to the bow. For energy calculations, the component of velocity perpendicular to the berthing line is required:

VB = V . sin Ѳ
α = drift angle of ship (true course)

Such manoeuvres are difficult and ship forward speed is quite low. Typical design values are:

V ≤ 1m/s
α ≤ 10°
Ѳ ≤ 5°
VB < 1.0 . sin (5°+ 10°) = 0.26m/s

The angle of the effective berthing line is larger for impacts closer to the bow, but the distance from centre of mass to point of impact (R) also increases. The value of the Eccentricity Factor (CE) needs careful consideration.

Single wheel fenders are used where there is small variation in water level. Multiple or “stacked” wheel fenders are used for large tides or water level changes.

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