Section 2.0
Mooring Restraint and
Environmental Criteria
2.1 GENERAL CONSIDERATIONS
In order to design a ship's mooring system, t.he environment loads likely ro act upon the ship must
first be determined. These can be higbly variable from terminal to terminal. To ensure a minimum
standard is mel for mooring eQuipmenl on ships engaged in worldwide trades, the Standard Environ-
mental Criteria given below should be assumed. The Standard EnvironmentaJ Criteria apply to
the design of the ship mooring sytem and arc nO! criteria for pier design nor a' required operating
capacity for a pier/ship mooring plan. These panuneters are Ilot i.ntended to cover the worst possible
conditions, since this would be neither practica.l nor reasonable. La situation.s where Ihe St.andard
Bnvironmental Criteria are exceeded, such as during hurricanes or at a river berth with extremely
st.rong current, additional measurcs must be taken such as doubling mooring lines, requesting tug
assistance or leaving the berth.
Environmental loads acting upon a ship due to wind and current should be derived from specific
model test data for tbat ship des ign or from the general non-dimensioual force coefficients for oil
tankers and g, carriers contained il\ Refere,nct' 3 and Reference 5.
The wind and current coefficien I-S contained in Reference 3 were defined originaJly for VLCC size
ships above 150,000 tonnes deadweighl. More reLent model test data on the modern tanker forms
which have all accommodation superstructures aft l:Onfirms lhat tllese same coefficiellts are, in most
cases, sufficiently accurate when applied ro smaller ships, and that ihey may therefore be used for
a range of ships down 10 approx.imalcly \6,000 tonnei; deadweighl.
For gas carriers (he wind coefficients quoted in Reference 5 are recommended. These apply to
membrane and spherical tank designs in t.he range 75,000 m) to 125,000 ml. For smaller gas carriers,
generally acceptable wind coefficiel1l data is not available and, unle.ss model tests are to be carried
out in each case, a conservalive extrapolation from large gas carrier data must be adopted.
The current coefficients quoted in Reference 3 for V LCCs may be lIsed for all sizes of tankers with
similar geometry down 10 16,000 tonnes deadweight and for gas carriers of an equivalent length and
draft.
It must be recognised that the coefficients contained in Reference 3 and Reference 5 will yield
accurate results only if the ves. e l geometry and drafts are similar to Ihose of tbe model., used in
establishing the coefficienlS. Re ference 3 contains ome general guidelines for adju~tment~ if the
acmal vessel geometry is outside Ihe model range. For instance, oil tanker models used correspond
10 typical pre-MARPOL vessels with a ralio of overall length to freeboard of 50-60, and a ratio of
balla t fn.:t:board to full load [r e board of 3.1: I Ruference J suggcS"ts that wind coefficie nt s for post
MARPOL (SBT and double hull) vessels (which generally have higher free board than pre-MARPOL
vessels) be obtained by interpolation or extrapolation on tbe basis of midships freeboard. The
transverse coefficieots will generally be higher for newer vessels in fuU load condition and may be
higher in ballast conditions depending on actual baJla t draft and lriOl. Likewise, current coefficients
containe.d in Reference 3 are b<.l e d o n vessels with a It:ng1h to beam ralio of 6.. ).5: I. Some ve. sel~
have a lower ralio, and Reference 3 indicates Ihal the longitudinal correm coefficient may be 25IJio
to 30070 higher with a length to beam ratio of 5.0.