Mooring Loads Due to Parallel Passing Ships - State Lands ...

Modification of PASS-MOOR
In order to improve the predictions from PASS-MOOR, the empirical correction
factors of Seelig (2001) were re-derived using the data obtained in the present study.
The following results were obtained:
Cx - empirical
30.0
25.0
20.0
15.0
10.0
5.0
0.0
C = 1 + 170 . e e
X
C = 1 + 052 . e e
Y
C = 1 + 048 . e e
M
2
( 2.94( Dd / )) ( −0. 08(( GB / ) −3)
)
2
( 4.33( Dd / )) ( −0. 08(( GB / ) −2)
)
2
( 387 . ( Dd / )) ( −008 . (( GB / ) −2)
)
These are shown graphically in Figure 22. As noted in Equation (4), the experimental
results for Fx- and M- were slightly higher than the corresponding positive values, so the
negative peaks of these parameters and Fy+ were used to develop equation (10).
These expressions have the same general form as those by Seelig in equation
(9). Several differences are noted however. First, the new correction for surge force is
a non-linear function of the draft-to-depth ratio. Seelig had more limited data and
adopted a linear relationship as there was insufficient data to adopt any other
functional form. The corrections for sway force and yaw moment retain the strong nonlinear
dependence on (D/d). Second, because PASS-MOOR generally under-predicts
the surge and sway force, the new corrections are larger in order to eliminate this bias.
Third, while Seelig found the same correction for sway force and yaw moment, the new
data suggests less correction is needed for the yaw moment than for sway force.
Predictions carried out using PASS-MOOR with the revised coefficients are
shown in
Figure 23.
0.0 2.0 4.0 6.0 8.0 10.0
G/B
D/d=0.90
D/d=0.82
D/d=0.76
D/d=0.44
D/d=0.26
Figure 22a. Surge force correction factor for PASS-MOOR from equation (10)
NFESC TR-6056-OCN
32
(10)