MSC.1/Circ.1175/Rev.1*
9 December 2020
_________________
* Re-issued to refer to
the correct resolution MSC.474(102)
in paragraph 2 of the cover sheet.
REVISED
GUIDANCE ON SHIPBOARD TOWING AND MOORING EQUIPMENT
1 The Maritime
Safety Committee, at its eightieth session (11 to 20 May 2005), approved
guidance concerning shipboard equipment, fittings and supporting hull
structures associated with towing and mooring for the uniform implementation of
SOLAS regulation II-1/3-8, adopted by resolution MSC.194(80), which became effective on 1
January 2007.
2 The Committee, at
its 102nd session (4 to 11 November 2020), having considered a proposal by the
Sub-Committee on Ship Design and Construction, at its sixth session, with a
view to ensuring a uniform approach towards the application of the provisions
of SOLAS regulation II-1/3-8, as amended by resolution MSC.474(102), which is
expected to become effective on 1 January 2024, approved the Revised guidance
on shipboard towing and mooring equipment, as set out in the annex.
3 This revised
guidance is applicable to ships constructed on or after 1 January 2024 and does
not supersede the Guidance on shipboard towing and mooring equipment
(MSC.1/Circ.1175) which remains applicable to ships constructed on or after 1
January 2007 but before 1 January 2024.
4 Member Governments
are invited to use the annexed guidance when applying the revised SOLAS
regulation II-1/3-8, and to bring it to the attention of all parties concerned.
ANNEX
SHIPBOARD EQUIPMENT, FITTINGS AND SUPPORTING HULL STRUCTURES
ASSOCIATED WITH TOWING AND MOORING
1 Application
1.1 Under regulation
II-1/3-8 of the 1974 SOLAS Convention, as adopted by resolution MSC.474(102),
new displacement type ships, except high-speed craft and offshore units, shall
be provided with arrangements, equipment and fittings of sufficient safe
working load to enable the safe conduct of all towing and mooring operations
associated with the normal operations of the ship. The arrangements, equipment
and fittings shall meet the appropriate requirements of the Administration or
an organization recognized by the Administration.
1.2 The Revised
guidance on shipboard towing and mooring equipment (MSC.1/Circ.1175/Rev.1)
should apply to ships constructed on or after 1 January 2024. To ships
constructed on or after 1 January 2007 and before 1 January 2024, the Guidance
on shipboard towing and mooring equipment (MSC.1/Circ.1175) should apply.
1.3 This circular
provides standards for the design and construction of shipboard fittings and
supporting hull structures associated with normal towing and mooring operations
in harbours or sheltered waters, which Administrations are recommended to
implement. This circular also contains design guidance for fittings of ships
that are further intended to be towed by another ship or tug, e.g. in an
emergency. This circular does not require tow lines nor mandate standards for
mooring lines on board the ship. Furthermore, this guidance is not applicable
to the design and construction of shipboard fittings and supporting hull
structures used for special towing services defined as:
.1 Escort towing:
Towing service required in some estuaries to control the ship in case of
failures of the propulsion or steering system. It should be referred to local
escort requirements;
.2 Canal transit
towing: Towing service for ships transiting canals, e.g. the Panama Canal.
It should be referred to local canal transit requirements; and
.3 Emergency towing
for tankers: Towing service to assist tankers in case of emergency. It
should be referred to paragraph 1 of SOLAS regulation II-1/3-4.
1.4 Equipment that is
used for both towing and mooring should be in accordance with sections 3 and 4.
2 Definitions
For the purpose of this guidance:
2.1 Normal towing
means towing operations necessary for manoeuvring in ports and sheltered waters
associated with the normal operations of the ship.
2.2 Other towing means
towing by another ship or a tug, such as to assist the ship in case of
emergency.
2.3 Shipboard
fittings mean bollards and bitts, fairleads, pedestal rollers and chocks
used for mooring of the ship and similar components used for normal or other
towing of the ship. Any weld, bolt or other fastening connecting the shipboard
fitting to the supporting hull structure is part of the shipboard fitting and
subject to any industry standard applicable to such fitting.
2.4 Supporting hull
structure means that part of the ship structure on/in which the shipboard
fitting is placed and which is directly submitted to the forces exerted on the
shipboard fitting. The hull structure supporting capstans, winches, etc. used
for normal or other towing and mooring operations mentioned above
should also be subject to this guidance.
2.5 Industry
standard means international or national standards which are recognized in
the country where the ship is built, subject to the approval of the
Administration.
2.6 Safe working
load (SWL) means the safe load limit of shipboard fittings used for mooring
operations in harbours or similar sheltered waters.
2.7 Safe towing load
(TOW) means the safe load limit of shipboard fittings used for normal and
other towing.
2.8 Ship Design
Minimum Breaking Load (MBLSD) means the minimum breaking load of
new, dry mooring lines for which shipboard fittings and supporting hull
structures are designed in order to meet mooring restraint requirements.
3 Towing
3.1 Strength
The strength of shipboard fittings used for normal towing
operations and their supporting hull structures should comply with the
provisions of 3.2 to 3.6. Where a ship is equipped with shipboard fittings
intended to be used for other towing services, the strength of these fittings
and their supporting hull structures should also comply with these provisions.
The strength of shipboard fittings intended to be used for both towing and
mooring and of their supporting hull structures should also comply with the
provisions of section 4.
3.2 Arrangements
Shipboard fittings for towing should be located on stiffeners
and/or girders which are part of the deck construction so as to facilitate
efficient distribution of the towing load. Other equivalent arrangements may be
accepted (for chocks in bulwarks, etc.), provided the strength is confirmed as
adequate for the intended service.
3.3 Load considerations
3.3.1 The minimum design
load applied to supporting hull structures for shipboard fittings should be:
.1 for normal towing
operations, 1.25 times the intended maximum towing load (e.g. static bollard
pull), as indicated on the towing and mooring arrangements plan;
.2 for other towing
services, the ship design minimum breaking load of the tow line defined in
appendix A; and
.3 for fittings
intended to be used for both normal and other towing operations, the greater of
the design loads according to .1 and .2.
3.3.2 The design load
should be applied to fittings in all directions that may occur by taking into
account the arrangement shown on the towing and mooring arrangements plan.
Where the towing line takes a turn at a fitting, the total design load applied
to the fitting is equal to the resultant of the design loads acting on the line.
However, in no case does the design load applied to the fitting need to be more
than twice the design load on the line as specified in 3.3.1 (see figure
below).
3.4 Shipboard fittings
3.4.1 Shipboard fittings
may be selected from an industry standard accepted by the Administration and at
least based on the following loads:
.1 for normal towing
operations, the intended maximum towing load (e.g. static bollard pull) as
indicated on the towing and mooring arrangements plan;
.2 for other towing
services, the ship design minimum breaking load of the tow line according to
appendix A; and
.3 for fittings
intended to be used for both normal and other towing operations, the greater of
the loads according to .1 and .2.
3.4.2 When the shipboard
fitting is not selected from an accepted industry standard, the strength of the
fitting and of its attachment to the supporting hull structure should be in
accordance with 3.3 and 3.5.
3.5 Supporting hull
structure
3.5.1 The reinforcing members
beneath shipboard fittings should be effectively arranged for any variation of
direction (horizontally and vertically) of the towing forces acting upon the
shipboard fittings. Proper alignment of fitting and supporting hull structures
should be ensured.
3.5.2 The acting point of
the towing force on shipboard fittings should be taken at the attachment point
of a towing line or at a change in its direction. For bollards and bitts the
attachment point of the towing line should be taken not less than 4/5 of the
tube height above the base (see figure below).
3.5.3 Under the design
load conditions as specified in 3.3 the allowable normal stress should be taken
as 100% and the allowable shearing stress as 60% of the specified yield point
for the material used. Normal stress is the sum of bending stress and axial
stress with the corresponding shearing stress acting perpendicular to the
normal stress. No stress concentration factors being taken into account.
3.6 Safe towing load
(TOW)
3.6.1 TOW used for normal
towing operations should not exceed 80% of the design load as given in 3.3.1.1
and TOW used for other towing operations should not exceed 80% of the design
load as given in 3.3.1.2. For fittings used for both, normal and other towing
operations, the greater of the safe towing loads should be used.
3.6.2 TOW, in tonnes, of
each shipboard fitting should be marked (by weld bead or equivalent) on the
fittings intended for towing. For fittings intended to be used for both, towing
and mooring, SWL, in tonnes, according to 4.6, should be marked in addition to
TOW.
3.6.3 The above provisions
on TOW apply for the use of no more than one towing line.
3.6.4 The towing and
mooring arrangements plan described in section 5 should define the method of
use of towing lines.
4 Mooring
4.1 Strength
The strength of shipboard fittings used for mooring operations and
of their supporting hull structures, as well as the strength of supporting hull
structures of winches and capstans, should comply with the provisions of 4.2 to
4.6. The strength of shipboard fittings, intended to be used for both, mooring
and towing, and of their supporting hull structures, should also comply with
the provisions of section 3.
4.2 Arrangements
Shipboard fittings, winches and capstans for mooring should be
located on stiffeners and/or girders, which are part of the deck construction,
so as to facilitate efficient distribution of the mooring load. Other
equivalent arrangements may be accepted (for chocks in bulwarks, etc.) provided
the strength is confirmed adequate for the service.
4.3 Load considerations
4.3.1 The minimum design
load applied to supporting hull structures:
.1 of shipboard
fittings should be 1.15 times the ship design minimum breaking load of the
mooring line provided in accordance with appendix A;
.2 of winches should be
1.25 times the intended maximum brake holding load, where the maximum brake
holding load should be assumed not less than 80% of the ship design minimum
breaking load of the mooring line according to appendix A; and
.3 of capstans 1.25
times the maximum hauling-in force.
4.3.2 The design load
should be applied to fittings in all directions that may occur by taking into
account the arrangement shown on the towing and mooring arrangements plan.
Where the mooring line takes a turn at a fitting, the total design load applied
to the fitting is equal to the resultant of the design loads acting on the
line. However, in no case does the design load need to be more than twice the
design load on the line as specified in 4.3.1 (see figure in 3.3).
4.4 Shipboard fittings
4.4.1 Shipboard fittings
may be selected from industry standards accepted by the Administration at least
based on the ship design minimum breaking load of the mooring line according to
appendix A.
4.4.2 When the shipboard
fitting is not selected from an accepted industry standard, the strength of the
fittings and of its attachment to the supporting hull structure should be in
accordance with 4.3 and 4.5.
4.5 Supporting hull
structure
4.5.1 Arrangement of
reinforcing members beneath shipboard fittings, winches and capstans should
consider any variation of direction (horizontally and vertically) of the
mooring forces acting upon the shipboard fittings. Proper alignment of fitting
and supporting hull structures should be ensured.
4.5.2 The acting point of
the mooring force on shipboard fittings should be taken at the attachment point
of a mooring line or at a change in its direction. For bollards and bitts the
attachment point of the mooring line should be taken not less than 4/5 of the
tube height above the base (see figure a) below). However, if fins are fitted
to the bollard tubes to keep the mooring line as low as possible, the attachment
point of the mooring line may be taken at the location of the fins (see figure
b) below).
4.5.3 Under the design
load conditions, as specified in 4.3, the allowable normal stress should be
taken as 100% and the allowable shearing stress as 60% of the specified yield
point for the material used. Normal stress is the sum of bending stress and
axial stress with the corresponding shearing stress acting perpendicular to the
normal stress, no stress concentration factors being taken into account.
4.6 Safe working load
(SWL)
4.6.1 The SWL, for the
purpose of marking, should be equal to the ship design minimum breaking load of
the mooring line according to appendix A.
4.6.2 The SWL, in tonnes,
of each shipboard fitting should be marked (by weld bead or equivalent) on the
fittings intended for mooring. For fittings intended to be used for both
mooring and towing, TOW, in tonnes, according to 3.6, should be marked in
addition to SWL.
4.6.3 The above provisions
on SWL apply for the use of no more than one mooring line.
4.6.4 The towing and
mooring arrangements plan described in section 5 should define the method of
use of mooring lines.
5 Towing and mooring
arrangements plan
5.1 The SWL and TOW for
the intended use for each shipboard fitting should be noted in the towing and
mooring arrangements plan available on board for the guidance of the master. It
should be noted that TOW is the load limit for towing purposes and SWL is the
load limit for mooring purposes.
5.2 Information provided
in the plan should include, in respect of each shipboard fitting:
.1 location on the
ship;
.2 fitting type;
.3 SWL/TOW;
.4 purpose (mooring,
normal towing or other towing); and
.5 method of applying
load of towing or mooring line including limiting fleet angle, i.e. angle of
change in direction of a line at the fitting.
5.3 Furthermore,
information provided on the plan is to include:
.1 the arrangement of
mooring lines showing number of lines (N);
.2 the ship design minimum
breaking load of each mooring line (MBLSD);
.3 the length of each
mooring line;
.4 restrictions or
limitations on the type (including material and construction), stiffness and
diameter of mooring lines which are compatible with the mooring equipment and
fittings; and
.5 the acceptable
environmental conditions as given in appendix A, section 3 for the recommended
ship design minimum breaking load of mooring lines for ships with Equipment
Number EN > 2000:
.1 30 second mean wind
speed from any direction (vW or vW* according to 3.1.3 or
3.2.2, respectively); and
.2 maximum current
speed acting on bow or stern (±10°).
Note:
When the applied design environmental
criteria exceed the above given criteria, information provided in the plan
should include the design environmental criteria, similar to the parameters in
appendix A:
.1 wind speed and
direction; and
.2 current speed and
direction.
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
(MBLSD). 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 < A/EN ≤ 1.1,
two
lines where 1.1 < A/EN ≤ 1.2,
three
lines where 1.2 < A/EN.
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.
Table 1: Mooring and tow lines for ships with EN ≤ 2000
|
EQUIPMENT NUMBER |
MOORING LINES |
TOW LINE* |
||
|
Exceeding |
Not exceeding |
No. of mooring lines |
Ship design minimum breaking load (kN) |
Ship design minimum breaking load (kN) |
|
1 |
2 |
3 |
4 |
5 |
|
50 |
70 |
3 |
37 |
98 |
|
70 |
90 |
3 |
40 |
98 |
|
90 |
110 |
3 |
42 |
98 |
|
110 |
130 |
3 |
48 |
98 |
|
130 |
150 |
3 |
53 |
98 |
|
150 |
175 |
3 |
59 |
98 |
|
175 |
205 |
3 |
64 |
112 |
|
205 |
240 |
4 |
69 |
129 |
|
240 |
280 |
4 |
75 |
150 |
|
280 |
320 |
4 |
80 |
174 |
|
320 |
360 |
4 |
85 |
207 |
|
360 |
400 |
4 |
96 |
224 |
|
400 |
450 |
4 |
107 |
250 |
|
450 |
500 |
4 |
117 |
277 |
|
500 |
550 |
4 |
134 |
306 |
|
550 |
600 |
4 |
143 |
338 |
|
600 |
660 |
4 |
160 |
370 |
|
660 |
720 |
4 |
171 |
406 |
|
720 |
780 |
4 |
187 |
441 |
|
780 |
840 |
4 |
202 |
479 |
|
840 |
910 |
4 |
218 |
518 |
|
910 |
980 |
4 |
235 |
559 |
|
980 |
1,060 |
4 |
250 |
603 |
|
1,060 |
1,140 |
4 |
272 |
647 |
|
1,140 |
1,220 |
4 |
293 |
691 |
|
1,220 |
1,300 |
4 |
309 |
738 |
|
1,300 |
1,390 |
4 |
336 |
786 |
|
1,390 |
1,480 |
4 |
352 |
836 |
|
1,480 |
1,570 |
5 |
352 |
888 |
|
1,570 |
1,670 |
5 |
362 |
941 |
|
1,670 |
1,790 |
5 |
384 |
1,024 |
|
1,790 |
1,930 |
5 |
411 |
1,109 |
|
1,930 |
2,080 |
5** |
437** |
1,168 |
|
2,080 |
2,230 |
** |
** |
1,259 |
|
2,230 |
2,380 |
** |
** |
1,356 |
|
2,380 |
2,530 |
** |
** |
1,453 |
|
2,530 |
- |
** |
** |
1,471 |
________________
* Information is provided
in relation to 3.3.1.2 and 3.4.1.2 of the annex to Revised guidance and
provision on board of such a line is not necessary under this guidance.
** For ships with EN >
2,000 see section 3 of appendix A.
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 vw, in m/s:
vw = 25.0 - 0.002(A1 - 2,000) for passenger
ships, ferries and car carriers with 2,000 m2 < A1 ≤
4,000 m2
= 21.0 for passenger ships, ferries
and car carriers with A1 > 4,000 m2
= 25.0 for other ships
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:
MBLSD = 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 vw,*
in m/s, can be estimated as follows:
where vw is the wind speed as per 3.1.3 above, MBLSD*
the breaking strength of the mooring lines intended to be supplied and MBLSD
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:
3.2.3 If lines are intended to be supplied for an acceptable wind
speed vw* higher than vw as per 3.1.3, the ship design
minimum breaking load should be taken as:
