UFC 4-159-03
3 October 2005
8-3.7
Wharf Mooring Concept. Camels and fenders are located between the
wharf and ship to offset the ship in this design. Also, the wharf breasting line bollards
are set back from the face of the wharf, so that the vertical angles of the breasting lines
are approximately 10 degrees. Figure 8-8, from a study of a number of ship moorings at
piers and wharves (NFESC TR-6005-OCN) is used to estimate that a mooring system
using synthetic lines will have an efficiency of approximately 0.67 for the case of
breasting lines with a 10-degree vertical angle. The estimated total required working
mooring line capacity is the working line capacity of the optimum ideal mooring divided
by the efficiency. In this case, the estimated working line capacity required is 1243
kips/0.67 or approximately 1855 kips.
For extra safety, the selected concept `Model 2' is given 11 mooring lines
of three parts each of aramid mooring line, as shown in Figure 8-9. A single part of line
is taken as having a break strength of 215 kips (9.2 E5 newtons). These lines have a
combined working strength of 11*3*215/3 = 2365 kips with a factor of safety of 3. These
lines are selected to provide extra safety. A component analysis, Figure 8-10, suggests
that this mooring concept has adequate mooring line capacity in the surge and sway
directions.
Quasi-static analyses are performed by computer using a fixed mooring
software program (W.S. Atkins Engineering Sciences, AQWA Reference Manual).
Analyses are performed for various wind directions around the wind rose. Results show
that the mooring line factors of safety are larger than the required minimum of 3 (i.e.,
line tensions divided by the new line break strength is less than 0.33), as shown in
Figure 8-11. In this concept the spring lines are especially safe with a factor of safety of
about 10. These analyses show ship motions of approximately 1 foot (0.3 meter) under
the action of the 75-mph (33.5-m/s) design winds.
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