3 October 2005
Forces/Moments. Methods in Section 4 are used to compute the forces
and moments on the ship. These values are summarized in Figure 8-4.
Definitions. In this example we define a global coordinate system with
"X" parallel to the wharf, as shown in Figure 8-5. Then "Y" is a distance perpendicular
to the wharf in a seaward direction and "Z" is a vertical distance. Let "Pt 2" be the ship
chock coordinate and "Pt 1" be the pier fitting. A spring line is defined as a line whose
angle in the horizontal plane is less than 45 degrees and a breasting line whose angle
in the horizontal plane is greater than or equal to 45 degrees, as shown in Figure 8-5.
Preliminary Analysis. The first step for fixed mooring design is to analyze
the mooring requirements for the optimum ideal mooring shown in Figure 8-6.
Analyzing the optimum ideal arrangement is recommended because: (1) calculations
can be performed by hand and; (2) this simple arrangement can be used as a standard
to evaluate other fixed mooring configurations (NFESC TR-6005-OCN, EMOOR - A
Quick and Easy Method for Evaluating Ship Mooring at Piers and Wharves.
The optimum ideal mooring shown in Figure 8-6 consists of two spring
lines, Lines 1 and 4, which are assumed to resist longitudinal forces. There are two
breast lines, Lines 2 and 3, which are assumed to resist lateral forces and moments for
winds with directions from 0 to 180 degrees. Fenders are not shown. All lines are
assumed to be parallel to the water surface in the ideal mooring.
A free body diagram is made of the optimum ideal mooring for a loaded
CVN-68 in 75-mph (33.5-m/s) winds. It is found that the sum of the working mooring
capacity required for Lines 1 and 4 is 174 kips (7.7 E5 newtons) and the sum of the
working mooring capacity required for Lines 2 and 3 is 1069 kips (4.76 E5 newtons), as
shown in Figure 8-7. Note that no working line capacity is required in the `Z' direction,
because the ship's buoyancy supports the ship. The sum of all the mooring line working
capacities for the optimum ideal mooring is 1243 kips (5.53 E6 newtons).