Appendix A - Mooring and Tow Lines

 1 General

1.1 The mooring lines for ships with Equipment Number (EN) of less than or equal to 2,000 are given in section 2. For other ships the mooring lines are given in section 3.

1.2 The applicable provisions for tow lines are given in section 2.

1.3 The EN should be calculated in compliance with appendix B. Deck cargo as given by the loading manual should be included for the determination of side-projected area A.

1.4 Sections 2 and 3 specify the minimum recommended number and minimum strength of mooring lines (MBL_SD). The designer should consider verifying the adequacy of mooring lines based on assessments carried out for the individual mooring arrangement, expected shore-side mooring facilities and expected prevalent environmental conditions.

 2 Mooring lines for ships with EN ≤ 2000 and tow lines

2.1 The minimum recommended mooring lines for ships having an EN of less than or equal to 2,000 are given in table 1.

2.2 For ships having the ratio A/EN > 0.9 the following number of lines should be added to the number of mooring lines as given in table 1:

• one line where 0.9 < ≤ 1.1,

• two lines where 1.1 < ≤ 1.2,

• three lines where 1.2 < .

2.3 The tow lines are given in table 1 and are intended as own tow line of a ship to be towed by a tug or another ship.

 3 Mooring lines for ships with EN > 2,000

3.1 General

3.1.1 The following is defined with respect to the purpose of mooring lines (see also figure below):

• .1 Breast line: A mooring line that is deployed perpendicular to the ship, restraining the ship in the off-berth direction;

• .2 Spring line: A mooring line that is deployed almost parallel to the ship, restraining the ship in fore or aft direction; and

• .3 Head/Stern line: A mooring line that is oriented between longitudinal and transverse direction, restraining the ship in the off-berth and in fore or aft direction. The amount of restraint in fore or aft and off-berth direction depends on the line angle relative to these directions.

  

• .4 Breast lines provide the maximum transverse restraint and spring lines the maximum longitudinal restraint against vessel movement in athwart and in fore-aft direction, respectively. Head and stern lines are much less effective for these purposes. The applied mooring layout should follow these principles as far as possible with respect to the port facilities and as far as reasonable with respect to the vertical line angles.

3.1.2 The strength of mooring lines and the number of head, stern and breast lines for ships with an EN > 2,000 are based on the side-projected area A₁. Side projected area A₁ should be calculated similar to the side-projected area A according to appendix B but considering the following conditions:

• .1 For oil tankers, chemical tankers, bulk carriers and ore carriers the lightest ballast draft should be considered for the calculation of the side-projected area A₁. For other ships the lightest draft of usual loading conditions should be considered if the ratio of the freeboard in the lightest draft and the full load condition is equal to or above two. Usual loading conditions mean loading conditions as given by the trim and stability booklet that are to be expected to regularly occur during operations, excluding light weight conditions, propeller inspection conditions, etc.

• .2 Wind shielding of the pier can be considered for the calculation of the side-projected area A₁ unless the ship is intended to be regularly moored to jetty-type piers. A height of the pier surface of 3 m above the waterline may be assumed, i.e. the lower part of the side-projected area with a height of 3 m above the waterline for the considered loading condition may be disregarded for the calculation of the side-projected area A₁.

• .3 Deck cargoes as given by the loading manual should be included for the determination of side-projected area A₁. Deck cargo may not need to be considered if a usual light draft condition without cargo on deck generates a larger side-projected area A₁ than the full load condition with cargo on deck. The larger of both side-projected areas should be chosen as side-projected area A₁.

3.1.3 The mooring lines as given hereunder are based on a maximum current speed of 1.0 m/s and the following maximum wind speed v_w, in m/s:

3.1.4 The wind speed is considered representative of a 30 second mean speed from any direction and at a height of 10 m above the ground. The current speed is considered representative of the maximum current speed acting on bow or stern (±10°) and at a depth of one-half of the mean draft. Furthermore, it is considered that ships are moored to solid piers that provide shielding against cross current.

3.1.5 Additional loads caused by, for example, higher wind or current speeds, cross currents, additional wave loads or reduced shielding from non-solid piers may need to be particularly considered. Furthermore, it should be observed that unbeneficial mooring layouts can considerably increase the loads on single mooring lines.

3.2 Ship design minimum breaking load

3.2.1 The ship design minimum breaking load, in kN, of the mooring lines should be taken as:

• MBL_SD = 0.1 · A₁ + 350

3.2.2 The ship design minimum breaking load may be limited to 1,275 kN (130 t). However, in this case the moorings are to be considered as not sufficient for environmental conditions given by A.3.1.3. For these ships, the acceptable wind speed v_w,^footnote in m/s, can be estimated as follows:

• v_w^footnote = v_w · ^footnote

where v_w is the wind speed as per 3.1.3 above, MBL_SD^footnote the breaking strength of the mooring lines intended to be supplied and MBL_SD the breaking strength as recommended according to the above formula. However, the ship design minimum breaking load should not be taken less than corresponding to an acceptable wind speed of 21 m/s:

• MBL_SD^footnote ≥ · MBL_SD

3.2.3 If lines are intended to be supplied for an acceptable wind speed v_w^footnote higher than v_w as per 3.1.3, the ship design minimum breaking load should be taken as:

• MBL_SD^footnote = ^footnote · MBL_SD

3.3 Number of mooring lines

3.3.1 The total number of head, stern and breast lines should be taken as:

• n = 8.3·10^-4 · A₁ + 6

3.3.2 For oil tankers, chemical tankers, bulk carriers and ore carriers, the total number of head, stern and breast lines should be taken as:

• n = 8.3·10^-4 · A₁ + 4

3.3.3 The total number of head, stern and breast lines should be rounded to the nearest whole number.

3.3.4 The number of head, stern and breast lines may be increased or decreased in conjunction with an adjustment to the strength of the lines. The adjusted strength, MBL_SD,^footnote should be taken as:

• MBLSDfootnote = 1.2 · MBLSD · n/nfootnote ≤ MBLSD	for increased number of lines,
  MBLSDfootnote = MBLSD · n/nfootnote	for reduced number of lines,

where MBL_SD is MBL_SD or MBL_SD^footnote specified in 3.2, as appropriate; n^footnote is the increased or decreased total number of head, stern and breast lines and n the number of lines for the considered ship type as calculated according to 3.3.1 or 3.3.2 without rounding.

3.3.5 Vice versa, the strength of head, stern and breast lines may be increased or decreased in conjunction with an adjustment to the number of lines.

3.3.6 The total number of spring lines should be taken not less than:

• two lines where EN < 5,000; and

  four lines where EN ≥ 5,000.

3.3.7 The strength of spring lines should be the same as that of the head, stern and breast lines. If the number of head, stern and breast lines is increased in conjunction with an adjustment to the strength of the lines, the number of spring lines should be taken as follows, but rounded up to the nearest even number:

• n_S^footnote = MBL_SD/ MBL_SD^footnote · n_S

where MBL_SD is MBL_SD or MBL_SD^footnote specified in 3.2, as appropriate, MBL_SD^footnote the adjusted strength of lines as specified in 3.3.4, n_S the number of spring lines as given in 3.3.6 and n_S^footnote the increased number of spring lines.