Page 6 - 4274

Wave Directional Spreading Function
Identification of effect of currents, seabed topography and
other factors likely to modify the above parameters
Current: Surface Current Speed
Surface Current Direction Current Profile (speed and
direction) Tidal Current Speed and Direction
Identification of low frequency components in current
velocities
Tide: Astronomical Tide
Storm Surge
Ice: The extent of snow and ice accumulation
Marine Growth: The extent to which marine growth may
form on the submerged sections of the marine vessels
Most metocean parameters vary with time in a random
manner, and extreme values to be used in design can only be
selected on a probabilistic basis.
Regulatory Framework
(I) Mobile Units
Most (though not all) maritime authorities require that
mobile offshore units comply with an internationally accepted
safety standard and, as with ships, the most effective way to
comply is to be in class such that the classification society can
issue the necessary certificates.
The most commonly used safety standard at the present
time is the Code for the Construction & Equipment of Mobile
Offshore Drilling Units (MODU Code). Prior to the introduction
of the MODU Code in 1979, surveys and certification for mobile
units were carried out under SOLAS and MARPOL.
Once a mobile unit is located on station and is engaged in
the exploration or exploitation of oil and gas, it becomes subject to
the regulations that apply in the waters of the coastal state. These
will be the same as those that apply to fixed installations in the
same waters although it is usual for mobile installations to also
maintain their class and statutory survey regime whilst on location
for the sake of convenience when it comes to moving on.
(II) Fixed Installations
Fixed installations, as their name implies, do not move
from location and there is therefore no international dimension to
their operations. They are regulated solely by the legislation that is
in force in their coastal state and this can vary from virtually zero
in some countries to the sophisticated goal setting and safety case

6