The number of lines required to hold a vessel in a given situation would have to be assesscd by
trial and error. Very approx-imatc solutions may be obtained by use of the formulae Listed in
Section 2.6. These may then be verified by a full calculation.Sample calculations have been worked out for a 250 kdwt tanker for both [he loaded and ballasted
conditions. Thesc aIe shown on pages 167 and 169.E.6 POSSIBLE REFINEMENTS OF CALCULA liON
I. When all the lines a rc wires filfed with synthetic tails, their elast.ic propenies and consequently
the load distribution are altered. Each tail may be considered as an equivalent wire whose lcngth
is gre.ater than that of the tail in proportion to the ratio of perce ntagc elongations of the tail and
the wire at the' sam e load (this allows for tail MBL greatcT than wire MBL). In the calculation
o nly L has to be modified. For example, if each line is fitted with an 11 m tail and the r atio
of percentage elongations is 10, then II x (l0 - I) = 99 m is added to the length of each line
already assessed.- Wberea shore pulley is provided (0 take a bigh,t of a vessel's tine, both legs are effective and
assume tbe same tensions. In tbe calcuIation for each leg the average vaJues of cos a, cos () and
L for the two legs should be used.
Caution is required if tails are included as the tail on the onc line is effec tively shared by t.he
two legs.- ID iH-conditjoned la youts with several lateral restraint lines laking up vertical inclinations of 25°
or more, the accuracy may be improved by use of a more complicate d formula:
LineI
2
3"' 56
78
910
11
12
13
14COS a. cos (}
critical line has highest value of
Lcosl a • cos! e
R y = 0. 55 (MBL). E -----
La.
'(' 111 H
plo"15.0^47 3.4
17.J 46 3.4
17.2 41.S 3A
14.2 37.5 3.4
12..4 35.5 3.49.0 68 3.4
8.8 69. 5 3.410 .2 60 .5 3 .4
10.4 S9 3.411.0 40 3.4
12.8 41.5 3.4
16 .0 44 3.4
10.2 58.5 3.4- 8 65 3.4
EXAMPLE-LOADED VESSEL
250000 d\\'l tanker on 19.2 m draft
14 no. 42 mm wires of MBL 1110 kN
Layout as shown in F igure B.2.0° Iou! + I," = L cos 0 cos a
true4.1 47 + 6 = 53 0.997 0 .966
4.2 46 + 6 >= (^52) 0.997 0 .955
4.7 41.5 + 42.5 = 84 0.997 0 .955
S.2 37.5 + 44 = 81.S 0.996 0.969
5.5 35.5 + 35 = 70. 5 0 .995 0.977
2.9 68 + 35 = 103 0.999 0.988
2.8 69.5 + 35 = 10·U 0.999 0.988
3.2 60.5 + 35 = 95.5 0.998 0.984
3.3 S9 + 35 = 94 0.998 0.984
4.9 40 + 32 = 72 0.996 0.982
4.7 41.5 + 32 = 73.5 0.997 0.975
4.4 44 + 7.5 = 51.5 0.997 0.9613 .3 58.5 + 6 = 64 .S 0.998 0.984
3.0 6S + 6 = 71 0,999 0.982
~ Indicatcs critical ~ne of ~oup.cos a cos^2
lOO-- lOO-
L L1.82 1.76
1.84* 1.75
1.I4 1.09
1.19 LIS
1.39 USL = 7. 10
1.36 1.34
1.33 1.29
1.87* 1.79
1.53 1.50
1.38 1.36- 1: "" 7.29