3 October 2005
BUOYS. There are two buoys commonly used on U.S. Navy Fleet
moorings: an 8-foot diameter buoy and a 12-foot diameter buoy. These buoys have a
polyurethane shell, are filled with foam, and have a tension bar to transmit mooring
loads to the chain. Properties of these buoys are given in Table 6-6. Some of the key
features of these buoys are that they require little maintenance and they are self-
fendering. A variety of older steel buoys in use are being phased out, due to their
relatively high maintenance cost. Some of the factors to consider in selecting the type
of mooring buoy to use are: availability, size, cost, durability, maintenance, inspection,
disposal and similar factors.
SINKERS. Sinkers are placed on fleet moorings to tune the static and
dynamic behavior of a mooring. Sinkers are usually made of concrete or low cost
metal. Key sinker parameters that can be specified in design include:
Special care needs to be taken in the design and inspection of lifting eyes and
attachment points on sinkers to ensure that they are safe.
MOORING LINES. The most common tension member lines used are
synthetic fiber ropes and wire rope. Synthetic lines have the advantage of easy
handling and some types have stretch, which can be used to fine tune static and
dynamic mooring behavior and aid in load sharing between tension members. Wire rope
has the advantage of durability.
Synthetic Fiber Ropes. Mooring lines are formed by weaving a number
of strands together to form a composite tension member. Lines are made of different
types of fiber and various constructions. Stretch/strain properties of selected lines are
shown in Table 6-7 and Figure 6-2. Engineering characteristics of some double braided
nylon and polyester lines are given in Tables 6-8 and 6-9. Additional information is
provided in NFESC TR-6014-OCN, Mooring Design Physical and Empirical Data. The
size and type of synthetic line specified in a given design will depend upon parameters
such as those shown in Table 6-10. A discussion of the use of various mooring line
types is given in Appendix A.