3 October 2005
Further quasi-static analyses show this concept is safe in up to 87-mph (38.9-m/s)
winds with a factor of safety of 3 or more on all the mooring lines. The computed
mooring efficiency for `Model 2' at this limiting safe wind speed is 0.705, which is slightly
higher than the estimated value of 0.67, as shown in Figure 8-5.
These preliminary calculations show that this fixed mooring concept could
safely secure the ship. Figure 8-12 illustrates the mooring concept in perspective view.
Further information on this example is provided in NFESC TR-6004-OCN, Wind Effects
on Moored Aircraft Carriers.
SPREAD MOORING - BASIC APPROACH. Design of a spread mooring
for a nest of ships is illustrated in this section.
Background for Example. SPRUANCE class (DD 963) destroyers are
scheduled for inactivation and a mooring is required to secure four of these vessels
(NFESC SSR-6119-OCN, D-8 Mooring Upgrade Design Report). These ships are
inactive and cannot go out to sea, so the mooring must safely secure the vessels in a
hurricane using Mooring Service Type IV design criteria. At this location, wind is the
predominant environmental factor of concern. At this site the tidal range and tidal
current are small. Soil conditions at the site consist of an upper soft silty layer between
50 to 80 feet in depth (15 to 24 meters) over a stiff clay underneath. Water depth at the
site ranges between 31 to 35 feet (9.4 to 10.7 meters) MLLW.
to moor four
DD 963 class destroyers
spread mooring. Use Mooring Service Type IV criteria and a design wind speed of 78.3
mph (68 knots or 35 m/s).
The ships are assumed
to be at one-third stores/cargo/ballast
condition, since DD-963 vessels are unstable in the light condition. Table 8-3 gives
some ship parameters. Additional information is found in the NAVFAC Ships