2 Vertical Still Water Hull Girder Loads

2.1 General

2.1.1 Seagoing and harbour/sheltered water conditions

The designer is to provide the permissible still water bending moment and shear force for seagoing and harbour/sheltered water operations.

The permissible still water hull girder loads are to be given at each transverse bulkhead in the cargo hold region, at the middle of cargo compartments, at the collision bulkhead, at the engine room forward bulkhead and at the mid-point between the forward and aft engine room bulkheads. The permissible hull girder bending moments and shear forces at any other position may be obtained by linear interpolation.

Note 1: It is recommended that, for initial design, the permissible hull girder hogging and sagging still water bending moments are at least 5% above the maximum still water bending moment from loading conditions in the loading manual, and the permissible hull girder shear forces are at least 10% above the maximum still water shear force from loading condition in the loading manual, to account for growth and design margins during the design and construction phase of the ship.

2.1.2 Flooded condition

The designer is to provide the envelope of permissible still water bending moment and shear force in flooded condition.

2.1.3 Still water loads for the fatigue assessment

The still water bending moment and shear force values and distribution to be used for the fatigue assessment are to be taken as the most typical values applicable for the loading conditions that the ship will operate in for most of its life. Typically, these conditions will be the normal ballast condition and full homogeneously loaded condition for double hull oil tankers. For bulk carriers, these will be the normal ballast condition, heavy ballast condition, full homogeneously loaded condition and full alternate loaded condition; note the latter is only applicable to BC-A bulk carriers. The definition of loading conditions to use is specified in Ch 9.

2.2 Vertical still water bending moment

2.2.1 Minimum still water bending moment

The minimum still water bending moment, M_sw-h-min and M_sw-s-min, in kNm, in hogging and sagging condition, respectively is to be taken as:

Hogging conditions:

M_{sw – h – min} = f_sw (171C_w L² B(C_B + 0.7) 10^–3 – M_{wv –
h – mid})

Sagging conditions:

M_{sw – s – min} = –0.85 f_sw (171C_w L² B(C_B + 0.7) 10^–3 + M_{wv –
s – mid})

where:

M_wv-h-mid : Vertical wave bending moment for strength assessment in hogging condition, as defined in [3.1.1] using f_p and f_m equal to 1.0.

M_wv-s-mid : Vertical wave bending moment for strength assessment in sagging condition, as defined in [3.1.1] using f_p and f_m equal to 1.0.

f_sw : Distribution factor along the ship length. To be taken as, see Figure 1:

f_sw = 0.0 for x ≤ 0
f_sw = 0.15 at x = 0.1 L
f_sw = 1.0 for 0.3 L ≤ x ≤ 0.7 L
f_sw = 0.15 at x = 0.9 L
f_sw = 0.0 for x ≥ L
Intermediate values of f_sw are to be obtained by linear interpolation.

Figure 1 : Distribution factor f_sw

2.2.2 Permissible vertical still water bending moment in seagoing condition

The permissible vertical still water bending moments, M_sw-h and M_sw-s in seagoing condition at any longitudinal position are to envelop:

The most severe still water bending moments calculated, in hogging and sagging conditions, respectively, for the seagoing loading conditions defined in Ch 4, Sec 8.
The most severe still water bending moments for the seagoing loading conditions defined in the loading manual.
The minimum still water bending moment defined in [2.2.1]

2.2.3 Permissible vertical still water bending moment in harbour/sheltered water and tank testing condition

The permissible vertical still water bending moments in the harbour/sheltered water and tank testing condition M_sw-p-h and M_sw-p-s at any longitudinal position are to envelop:

The most severe still water bending moments, in hogging and sagging conditions, respectively, for the harbour/sheltered water loading conditions defined in Ch 4, Sec 8.
The most severe still water bending moments for the harbour/sheltered water loading conditions defined in the loading manual.
The permissible still water bending moment defined in [2.2.2].
The minimum still water bending moment defined in [2.2.1] increased by 25%.

2.2.4 Permissible vertical still water bending moment in flooded condition at sea

The permissible vertical still water bending moments in flooded condition M_sw-f at any longitudinal position are to envelop:

The most severe still water bending moments, in hogging and sagging conditions, respectively, for the intact and flooded seagoing loading conditions defined in Ch 4, Sec 8. Loading conditions encountered during ballast water exchange need not to be considered for the flooded condition.
The most severe still water bending moments for the intact and flooded seagoing loading conditions defined in the loading manual.
The permissible still water bending moment defined in [2.2.2] increased by 10%.

2.3 Vertical still water shear force

2.3.1 Minimum still water shear force in seagoing conditions for oil tankers

The minimum hull girder positive and negative vertical still water shear force, Q_sw-min in kN, in way of transverse bulkheads between cargo tanks in the seagoing condition is to be taken as:

a) For oil tankers with three cargo tanks across the breadth of the ship:
and is to be taken as the maximum value of Q_sw-min calculated for cargo/ballast tanks forward and aft of the transverse bulkhead.
b) For oil tankers with two cargo tanks across the breadth of the ship:
and is to be taken as maximum value of Q_sw-min calculated for cargo/ballast tanks forward and aft of the transverse bulkhead.

where:

B_local : Local breadth, in m, at T_SC at the middle length of the tank under consideration.

_tk : Length of cargo tank under consideration, in m, taken at the forward or aft side of the transverse bulkhead under consideration, in m.

V_CT : Volume of centre cargo tank, in m³, taken for the cargo tank on the forward or aft side of the transverse bulkhead under consideration.

V_ST : Volume of side cargo tank, in m³, taken for the cargo tank on the forward or aft side of the transverse bulkhead under consideration.

2.3.2 Minimum still water shear force in harbour/sheltered water conditions for oil tankers

The minimum hull girder positive and negative vertical still water shear force, Q_sw-p-min in kN in the harbour/sheltered water condition in way of transverse bulkheads between cargo tanks are to be taken as:

a) For oil tankers with three cargo tanks across the breadth of the ship:
and is to be taken as the maximum value of Q_sw-p-min calculated for cargo/ballast tanks forward and aft of the transverse bulkhead.
b) For oil tankers with two cargo tanks across the breadth of the ship:
and is to be taken as maximum value of Q_sw-p-min calculated for cargo/ballast tanks forward and aft of the transverse bulkhead.

2.3.3 Permissible still water shear force in seagoing condition

The permissible vertical still water shear forces, Q_sw for oil tankers and bulk carriers, in seagoing condition at any longitudinal position are to envelop:

The most severe still water shear forces, positive or negative, for the seagoing loading conditions defined in Ch 4, Sec 8 after shear force correction in case of bulk carrier.
The most severe still water shear forces for the seagoing loading conditions defined in the loading manual after shear force correction in case of bulk carrier.
For oil tankers, the minimum still water shear forces for seagoing conditions defined in [2.3.1].

2.3.4 Permissible still water shear force in harbour/sheltered water and tank testing condition

The permissible vertical still water shear forces, Q_sw-p for oil tankers and bulk carriers, in the harbour/sheltered water and tank testing condition at any longitudinal position are to envelop:

The most severe still water shear forces, positive or negative, for the harbour/sheltered water loading conditions defined in Ch 4, Sec 8 after shear force correction in case of bulk carrier.
The most severe still water shear forces for the harbour/sheltered water loading conditions defined in the loading manual after shear force correction in case of bulk carrier.
For oil tankers, the minimum still water shear forced for harbour/sheltered water conditions defined in [2.3.2].

The following value may be used as guidance at preliminary design stage:

Q_{sw – p} = Q_sw + 0.6Q_wv

where:

Q_sw : Permissible still water shear force Q_sw, as defined in [2.3.3].

Q_wv : Vertical wave shear force for strength assessment Q_wv-pos and Q_wv-neg, as defined in [3.2.1] using f_p equal to 1.0.

2.3.5 Permissible still water shear force in flooded condition at sea

The permissible vertical still water shear forces, Q_sw-f for oil tankers and bulk carriers, in flooded condition at any longitudinal position are to envelop:

The most severe still water shear forces, positive or negative, for the flooded seagoing loading conditions defined in Ch 4, Sec 8 after shear force correction in case of bulk carrier. Loading conditions encountered during ballast water exchange need not be considered for the flooded condition.
The most severe still water shear forces for the flooded seagoing loading conditions defined in the loading manual after shear force correction in case of bulk carrier.
The permissible still water shear force is defined in [2.3.3].