OCIMF_Mooring_Equipment_Guidelines_(Second_Edition)

The appropriate formulae for mooring restraint requirements per Section 2.6 are less sensitive to
freeboard changes (since tbe breast line requiremeots are based on the transverse coefficient at the
aft perpendicular, where the differences between fuJI load and ballast coefficients are much smaller
than for the total latcral coefficients). Therefore, tbese formulae may be used also for newer vessels
with higher freeboard.

2.2 STANDARD ENVIRONMENTAL CRITERIA

For all tankers above 16,000 tonnes deadweight intended for general worldwide trading, the mooring
restraint available onboard the ship as permanent equipment should be sufficient to satisfy the
following conditions:

60 knots wind from lln~' di.reclion simultaneously with either:

J knots curren t at 00 or 1800 ;

or

2 knots current al 100 or 1700 ;.

or

0.75 knots current from tbe direction of maximum beam current loading.

Water depth to draft ratios for these conditions are to be lakeo as 1.1: I when loaded and 3.0: I

when in ballast.

While a number of tenuioals have a minimum depth to draught ratio alongside the berth of 1.05: I
this ratio will inevitably prevail around low slack water wben average curreot velocities would be less
tban when lhe water level is at a depth to draught ratio of 1.1: I. 11 is therefore suggested that the
average velocities previously recommended be used witb the 1.1: I ratio.

Obviously when a lerminal designer is reviewing the need for shore augmentation, he will find it

necessary to be more precise and should use actual site data for his calculations.

The ballast coorution is to correspond to the mean 1 MO ballast draft given approximately by

0.02LBP + 2.0m.

Wind velocity is the velocity measured at the standard datum height of 10 m above ground/water

surface and is representative of a 30 second average mean velocity. The seleclioo of the 30 second

wind is based on the time it takes the forces in a mooring system to respond to wind velocity changes.

Thirty seconds is a typical value for a baJlasted VLCC. Smaller vessels will respond more quickly;

and a fully laden VLCC may require 60 seconds to respond. However, for consistency, a 30 second

average period is suggested for aJI vessel sizes and loading condilions.

The current velocity is to be taken as the average velocity over the draft of the ship.

For gas carriers above 150 melres in length the same standard environmental criteria should be

applied. However. the water depth [0 draft ratio should be taken as 1.1: 1 for all conditions. since

the draft of a gas carrier changes little during nonnal cargo transfer operations.

The above criteria are intended to cover conditions that could readily be encountered on worldwide

trade, but (hey cannot possibly cater for the most extreme combination of environmental conditions

at every terminal worldwide. Panicularly exposed terminals, or those where for some reason !.he cri-

teria are likely to be exceeded, are expected to supplement ships' mooring restraint with appropriate

shore-based equipment.

Where a ship is operating exclusively on a dedicated route using tenninals whose specific environ-

mental data is available the recommended criteria way be revised to suit the local conditions.