3 October 2005
Design Methods. All moorings should be designed by
skilled/knowledgeable professional personnel. Methods must be used that assure that
ships are safely moored. Below are some guidelines.
Mooring Service Type I and II moorings can often be designed using
quasi-static tools with 3 degrees-of-freedom (surge, sway and yaw). Examples of tools
include FIXMOOR (Note: FIXMOOR is available from NAVFAC Atlantic CIENG
WATERS TOOLBOX; hereinafter referred to as WATERS TOOLBOX), OPTIMOOR,
AQWA LIBRIUM, etc. Specialized tools need to be considered for cases of high
currents, high tidal ranges, passing ship effects, ship waves, multiple/nested ships,
situations that are likely to be dynamic and other specialized cases. It is valuable to
ships' and port operations personnel to provide generalized mooring designs for
Mooring Service Types I and II.
Mooring Service Types III and IV must be designed on a case-by-case
basis using dynamic methods because of the extremely high loading that occurs during
extreme storms. It is recommended that NFESC be contacted concerning the design of
these types of moorings.
General Mooring Integrity. For multiple-member moorings, such as for a
ship secured to a pier by a number of lines, the mooring system strongly relies on load
sharing among several members. If one member is lost, the ship should remain
moored. Therefore, design multiple member mooring to ensure that remaining members
maintain a factor of safety at least 75 percent of the intact mooring factors of safety
shown in Table 3-7 with any one member missing.
Quasi-Static Safety Factors. Table 3-7 gives recommended minimum
factors of safety for "quasi-static" design based on material reliability.
Allowable Ship Motions. Table 3-8 gives recommended operational ship
motion criteria for moored vessels. Table 3-8(a) gives maximum wave conditions for
manned and moored small craft (Permanent International Association of Navigation
Congresses (PIANC), Criteria for Movements of Moored Ships in Harbors; A Practical
Guide, 1995). These criteria are based on comfort of personnel on board a small boat,
and are given as a function of boat length and locally generated.
Table 3-8(b) gives recommended motion criteria for safe working
conditions for various types of vessels (PIANC, 1995).
Table 3-8(c) gives recommended velocity criteria and Table 3-8(d) and (e)
give special criteria.