OCIMF_Mooring_Equipment_Guidelines_(Second_Edition)

Reasonably symmetrical layouts.

Venical line angles (8) less than 250 •

Head and stern line deviations from breast (0) kss than 45".

All lines of similar material, cOllstruction, make-up and size.

Lateral lines effectively grouped at head and stem.

It must be understood that tbis method only covers static strengtb requirements for a mooring

system. ~t does not make allowance for dynamic effects) neither does it evaluate vessel movements

under imposed loading. These must be considered separately.

E.S CALCULATION PROCEDURE

(Note: for spring lines substitute (3 for a)

1. Divide the mooring lines into groups for the different functions, i.c., lateral restraint at bow and
   at stem and longitudinal restraint forward and aft.


2. Assess the relevant parameters a, 8. L. = I (outboard) + 1 (inboard) for each line .. Depending
   on the accuracy required and personal preference. scale drawings or calculations may be used.
   Secondary parameters such as H, the height difference between jell), hook and vessel fai rlead ,
   may be int.roduced. The results are best tabulated as shown in the example .. A s regards accuracy.
   the procedure already includes a number of approximations which for mos( layouts have little
   effect. Furtber approximations may be made at this stage. e.g.,

Take average values for grouped lines.

Take on.iy plan lengths of lines. ignoring correction for slope.

3. Evu.luflte and t.abulat.;! cos c, cos 0 for each line.
   Cos'a


4. EvaJuate and tabulate --L for each line a.nd total (svmbol. L) for each group. In the examples

a constant of 100 is introduced for convenience. It is eliminated in the last line of the calculation.

5. Assess for each group the critical line, i.e., the one that will break or ,Up first. This is the Lioe
   cos a
   witb the bighest value of --. I! is the most efficiently placed line, with low values of c and
   L
   L. Subscript c is used to identify the relevant parameters.


6. Final step for each group:

la1eral restraint

COsla

R r =-0.55 (MBL). L--

L

which has to resist the imposed load.

The nominal remaint capability of the lines is:

nom R r = 0.55 (MBL). N where N = no. of lines

nomRr

efficiency of layout =

R.,.

longitudinal restraint may be calculated by a simi.lar formula, but often t.he lines bave very similar

values of L. {J. 8 and an approximation may be used:

Rx = 0.55 (MBL). cos Pr. cos Or