8.1.2 Mooring forces on piles
Mooring structures are not required to carry any pull from ropes during the operation of
berthing ships other than a restraining longitudinal movement at the final stages of the
berthing operation.
When the ship is fully moored four ropes are attached to bollards or bitts fixed to the jetty
structure or mounted on independent mooring dolphins in positions such as those shown in
Figure 8.7. Using this type of layout the ship is restrained from excessive ranging against the
fenders and also from moving away from the berth under the influence of offshore waves or
currents. The load on any individual rope due to winds or currents acting on the ship or to
checking the way of a ship during berthing cannot be calculated with any accuracy.
It depends on the tensioning of the rope and its angle to the berthing line.
The wind and current forces on the ship can be calculated using the equations given
below for calculating the current force on a pile (equation 8.10) or the wind force on a pile
(equation 8.14).
Mooring dolphins should be designed to be as rigid as possible. This is to restrict the
ranging of ships which is exaggerated by the lifting and sagging of the mooring ropes.
Independent mooring dolphins can take the form of pile groups set back from the berthing
line as shown in Figure 8.7, or placed beyond the ends of the berthing head. Piles in mooring
dolphins can be raked in two directions to resist longitudinal, transverse and torsional pulls
(Figure 8.10). Where rock is present at or at a short distance below the sea bed, anchorages
are required to withstand the uplift on tension piles as described in Section 6.2.4.
Guidance on the design of mooring structures is given in Part 4 of BS6349.
8.1.3 Wave forces on piles
Jetties are normally sited in sheltered waters or in locations selected as not being subject to
severe storm waves. Consequently, the forces on piles due to wave action are considerably
less severe than those caused by the impact from berthing or the pull from mooring ropes.
Also, berthing operations are not expected to take place when heavy wave action is occur-
ring. Therefore, it is the usual practice to disregard wave forces on piles forming the berthing
head of a jetty and any associated independent dolphin structures where these are sited in
Piling for marine structures 407Figure 8.10Mooring dolphin with piles raked in two directions.Bollard