1 -5 F(!)l'Ward Breast LInes
10-14 Aft Breast LJnes
6·9 Sp"ng~!JJ.QQru:Q...l&agtb,LOf lines
length Length
Line No. In Metres line No. In Metres(^1 6 8 35)
2 6 9 35
3 42.5 (^10 32)
4 44
5 35 l' 12 7.5^32
(^6 35 13 6)
7 35 14 6
FIGURE 2.9: MOORING LAYOUT USED FOR COMPUTATIONAL PURPOSES
Pre-tensioning of the mooring lines may be taken into account in determining the mooring line
forces. When this is done, tbe force calculated in Step 4 is added to the pre-tension force. The
mooring line force calculated in Step 4 may be negative reducing the pre-tension provided. that [he
net load is never negative. The pre-tension forces in the lines and the forces in the breasling dolphins
should be in equilibrium before applying forces due to wind, currenr and other environmental factors.
2.5.3 Hand Calculation Procedures
Tbe hand calculation method for assessing tbe restraint capabilities of mooring layouts is intended
for use when circumstances preclude (he application of more sophisticated computer O'lethods. Tn
addition, it can be used to improve the quantitative understanding of good mooring principles_
The method is described in det.ail in Appendix D.
It uses the basic principles outlined. earlier in this chapter but includes a Dumber of assumptions and
approximations to yield a workable procedure. As a result it is reasonably accurate provided certain
limitations are observed. The mooring layout should comply witn the Principles of Mooring given i.n
Section t, notably the separation of lateral and longitudinal restraint functions, symmetry of layout.
avoidance of poorly angled head and stem lines, similarity of line type and size. If such criteria are
observed the answers produced are within IOOJo of those from computer methods. Bearing in mind
the accuracy of other input data, it is considered Ihat th.e method has quite adequate validity jf
applied with discretion.
Appendix D includes a worked example and the results are compared with a computer method
solution. The particuJar mooring layout used is well-conditioned and thus tbe results agree quite
closely wit h I hose of the computer method.
Another way to derermine a vessel's general monring line requirement without [he knowledge of a
specific tenninal geometry is to base the requirement on the maximum components of the eovi-
ronmental forces. and an efficiency factor for each line group. Such method is (he basis for the