Annex 12 - Criteria for Longitudinal
Strength of Hull Girder for Oil Tankers
1.1 These criteria should be used for the evaluation
of longitudinal strength of the ship's hull girder as required by
1.2 In order that ship's longitudinal strength
to be evaluated can be recognized as valid, fillet welding between
longitudinal internal members and hull envelopes should be in sound
condition so as to keep integrity of longitudinal internal members
with hull envelopes.
2 Evaluation of longitudinal strength
On oil tankers of 130 m in length and upwards and of over
10 years of age, the longitudinal strength of the ship's hull girder
should be evaluated in compliance with the requirements of this annex
on the basis of the thickness measured, renewed or reinforced, as
appropriate, during the renewal survey of the Cargo Ship Safety Construction
Certificate or Cargo Ship Safety Certificate (SC renewal survey).
The condition of the hull girder for longitudinal strength
evaluation should be determined in accordance with the methods specified
in appendix 3.
2.1 Calculation of transverse sectional
areas of deck and bottom flanges of hull girder
2.1.1 The transverse sectional areas of deck flange
(deck plating and deck longitudinals) and bottom flange (bottom shell
plating and bottom longitudinals) of the ship's hull girder should
be calculated by using the thickness measured, renewed or reinforced,
as appropriate, during the SC renewal survey.
2.1.2 If the diminution of sectional areas of
either deck or bottom flange exceeds 10 % of their respective as-built
area (i.e. original sectional area when the ship was built), either
one of the following measures should be taken:
.1 to renew or reinforce the deck or bottom flanges
so that the actual sectional area is not less than 90% of the as-built
.2 to calculate the actual section moduli (Zact)
of transverse section of the ship's hull girder by applying the calculation
method specified in appendix 1, by using the thickness measured, renewed
or reinforced, as appropriate, during the SC renewal survey.
2.2 Requirements for transverse section modulus
of hull girder
2.2.1 The actual section moduli of transverse
section of the ship's hull girder calculated in accordance with paragraph
188.8.131.52 should satisfy either of the following provisions, as applicable:
.1 for ships constructed on or after 1 July 2002,
the actual section moduli (Zact
) of the transverse
section of the ship's hull girder calculated in accordance with the
requirements of paragraph 184.108.40.206 should be not less than the diminution
limits determined by the Administration, taking into account the recommendations
adopted by the Organization; or
.2 for ships constructed before 1 July 2002, the
actual section moduli (Zact
) of the transverse
section of the ship's hull girder calculated in accordance with the
requirements of paragraph 220.127.116.11 should meet the criteria for minimum
section modulus for ships in service required by the Administration
or recognized classification society, provided that in no case Zact
should be less than the diminution limit of the minimum
section modulus ( Zmc
) as specified in appendix
Appendix 1 - Calculation Criteria Of Section Moduli Of Midship
Section Of Hull Girder
1 When calculating the transverse section modulus
of the ship's hull girder, the sectional area of all continuous longitudinal
strength members should be taken into account.
2 Large openings, i.e. openings exceeding 2.5m
in length or 1.2m in breadth and scallops, where scallop welding is
applied, are always to be deducted from the sectional areas used in
the section modulus calculation.
3 Smaller openings (manholes, lightening holes,
single scallops in way of seams, etc.) need not be deducted provided
that the sum of their breadths or shadow area breadths in one transverse
section does not reduce the section modulus at deck or bottom by more
than 3% and provided that the height of lightening holes, draining
holes and single scallops in longitudinals or longitudinal girders
does not exceed 25% of the web depth, for scallops maximum 75mm.
4 A deduction-free sum of smaller opening breadths
in one transverse section in the bottom or deck area of 0.06 (B - Sb) (where B = breadth of ship, Sb =
total breadth of large openings) may be considered equivalent to the
above reduction in sectional modulus.
5 The shadow area will be obtained by drawing
two tangent lines with an opening angle of 30°.
6 The deck modulus is related to the moulded deck
line at side.
7 The bottom modulus is related to the base line.
8 Continuous trunks and longitudinal hatch coamings
should be included in the longitudinal sectional area provided they
are effectively supported by longitudinal bulkheads or deep girders.
The deck modulus is then to be calculated by dividing the moment of
inertia by the following distance, provided this is greater than the
distance to the deck line at side:
from neutral axis to top of continuous strength member
from top of continuous strength member to centreline of the ship
x and y to be measured to the point
giving the largest value of y
9 Longitudinal girders between multi-hatchways
will be considered by special calculations.
Appendix 2 - Diminution Limit Of Minimum Longitudinal Strength
Of Ships In Service
2 Scantlings of all continuous longitudinal members
of the ship's hull girder based on the section modulus requirement
in 1 above should be maintained within 0.4 L amidships.
However, in special cases, based on consideration of type of ship,
hull form and loading conditions, the scantlings may be gradually
reduced towards the end of 0.4 L part, bearing in mind
the desire not to inhibit the ship"s loading flexibility.
3 However, the above standard may not be applicable
to ships of unusual type or design, e.g. for ships of unusual main
proportions and/or weight distributions.
Appendix 3 - Sampling method of thickness measurements for
longitudinal strength evaluation and repair methods
1 Extent of longitudinal strength evaluation
Longitudinal strength should be evaluated within 0.4L amidships
for the extent of the hull girder length that contains tanks therein
and within 0.5L amidships for adjacent tanks which may extend beyond
0.4L amidships, where tanks means ballast tanks and cargo tanks.
2 Sampling method of thickness measurement
2.1 Pursuant to the requirements of section 2.5
of Annex B, transverse sections should be chosen such that thickness
measurements can be taken for as many different tanks in corrosive
environments as possible, e.g. ballast tanks sharing a common plane
boundary with cargo tanks fitted with heating coils, other ballast
tanks, cargo tanks permitted to be filled with sea water and other
cargo tanks. Ballast tanks sharing a common plane boundary with cargo
tanks fitted with heating coils and cargo tanks permitted to be filled
with sea water should be selected where present.
2.2 The minimum number of transverse sections
to be sampled should be in accordance with annex 2 to Annex B. The
transverse sections should be located where the largest thickness
reductions are suspected to occur or are revealed from deck and bottom
plating measurements prescribed in 2.3 and should be clear of areas
which have been locally renewed or reinforced.
2.3 At least two points should be measured on
each deck plate and/or bottom shell plate required to be measured
within the cargo area in accordance with the requirements of annex
2.4 Within 0.1D (where D is the ship's moulded
depth) of the deck and bottom at each transverse section to be measured
in accordance with the requirements of annex 2, every longitudinal
and girder should be measured on the web and face plate, and every
plate should be measured at one point between longitudinals.
2.5 For longitudinal members other than those
specified in 2.4 to be measured at each transverse section in accordance
with the requirements of annex 2, every longitudinal and girder should
be measured on the web and face plate, and every plate should be measured
at least in one point per strake.
2.6 The thickness of each component should be
determined by averaging all of the measurements taken in way of the
transverse section on each component.
3 Additional measurements where the longitudinal
strength is deficient
3.1 Where one or more of the transverse sections
are found to be deficient in respect of the longitudinal strength
requirements given in this annex, the number of transverse sections
for thickness measurement should be increased such that each tank
within the 0.5L amidships region has been sampled. Tank spaces that
are partially within, but extend beyond, the 0.5L region, should be
3.2 Additional thickness measurements should also
be performed on one transverse section forward and one aft of each
repaired area to the extent necessary to ensure that the areas bordering
the repaired section also comply with the requirements of Annex B.
4 Effective repair methods
4.1 The extent of renewal or reinforcement carried
out to comply with this annex should be in accordance with 4.2.
4.2 The minimum continuous length of a renewed
or reinforced structural member should be not less than twice the
spacing of the primary members in way. In addition, the thickness
diminution in way of the butt joint of each joining member forward
and aft of the replaced member (plates, stiffeners, girder webs and
flanges, etc.) should not be within the substantial corrosion range
(75% of the allowable diminution associated with each particular member).
Where differences in thickness at the butt joint exceed 15% of the
lower thickness, a transition taper should be provided.
4.3 Alternative repair methods involving the fitting
of straps or structural member modification should be subject to special
consideration. In considering the fitting of straps, it should be
limited to the following conditions:
.1 to restore and/or increase longitudinal strength;
.2 the thickness diminution of the deck or bottom
plating to be reinforced should not be within the substantial corrosion
range (75% of the allowable diminution associated with the deck plating);
.3 the alignment and arrangement, including the
termination of the straps, is in accordance with a standard recognized
by the Administration;
.4 the straps are continuous over the entire 0.5L
amidships length; and
.5 continuous fillet welding and full penetration
welds are used at butt welding and, depending on the width of the
strap, slot welds. The welding procedures applied should be acceptable
to the Administration.
4.4 The existing structure adjacent to replacement
areas and in conjunction with the fitted straps, etc. should be capable
of withstanding the applied loads, taking into account the buckling
resistance and the condition of welds between the longitudinal members
and hull envelope plating.