3 External Impact Pressures for the Bow Area

3.1 Application

3.1.1 The impact pressures for the bow area are only to be applied for strength assessment.

3.2 Bottom slamming pressure

3.2.1 The bottom slamming pressure PSL, in kN/m², for the bottom slamming design load scenario is to be evaluated for the following two cases:

Case 1: An empty ballast tank or a void space in way of the bottom shell.

for L < 170 m

for L ≥ 170 m

Case 2: A full ballast tank in way of the bottom shell.

for L < 170 m

for L ≥ 170 m

where:

c₁ : Coefficient to be taken as:

c₁ = 0 for L ≤ 180 m
c₁ = –0.0125(L – 180)^0.705 for L > 180 m

c_SL-et : Slamming coefficient for case with an empty ballast tank or void space:

c_SL-ft : Slamming coefficient for case with a full ballast tank:

f_SL : Longitudinal slamming distribution factor, to be taken as:

f_SL = 0 for x ⁄ L ≤ 0.5
f_SL = 1.0 for x ⁄ L = 0.5 + c₂
f_SL = 1.0 for x ⁄ L = 0.65 + c₂
f_SL = 0.5 for x ⁄ L ≥ 1
Intermediate values of f_SL are to be obtained by linear interpolation.

c₂ : Coefficient to be taken as:

but not to be taken greater than 0.35.

T_F-e : Design slamming draught at the FP to be provided by the Designer. T_F-e is not to be greater than the minimum draught at the FP indicated in the loading manual for all seagoing conditions where any of the ballast tanks within the bottom slamming region are empty. This includes all loading conditions with tanks inside the bottom slamming region that use the ‘sequential’ ballast water exchange method, if relevant.

T_F-f : Design slamming draught at the FP to be provided by the Designer. T_F-f is not to be greater than the minimum draught at the FP indicated in the loading manual for all seagoing conditions where all ballast tanks within the bottom slamming region are full. This includes all loading conditions with tanks inside the bottom slamming region that use the ‘flow-through’ ballast water exchange method, if relevant.

z_top : Z-coordinate of the highest point of the tank, excluding small hatchways, in m.

For strength assessment of double bottom floors and girders, z_top is not to be taken greater than the double bottom height.

3.2.2 Loading manual information

The loading guidance information is to clearly state the design slamming draughts and the ballast water exchange method used for each ballast tank, if any.

Figure 12 : Definition of bow geometry

3.3 Bow impact pressure

3.3.1 Design pressures

The bow impact pressure P_FB, in kN/m², to be considered for the bow impact design load scenario is to be taken as:

where:

f_FB : Longitudinal bow flare impact pressure distribution factor. To be taken as:

f_FB = 0.55 for x ⁄ L ≤ 0.9
f_FB = 4 (x ⁄ L – 0.9) + 0.55 for 0.9 < x ⁄ L ≤ 0.9875
f_FB = 8(x ⁄ L – 0.9875) + 0.9 for 0.9875 < x ⁄ L ≤ 1.0
f_FB = 1.0 for x ⁄ L > 1.0

V_im : Impact speed, in knots, to be taken as:

V_ref : Forward speed, in knots, to be taken as:

V_ref = 0.75 V but not less than 10.

α_wl : Local waterline angle, in deg, at the considered position, but not less than 35 deg. See Figure 12.

γ_wl : Local bow impact angle, in deg, measured in a vertical plane containing the normal to the shell, from the horizontal to the tangent line at the considered position but not less than 50 deg, as shown in Figure 12. Where this value is not available, it may be taken as:

β_pl : Local body plan angle, in deg, at the considered position from the horizontal to the tangent line, but not less than 35 deg.

c_FB : Coefficient to be taken as:

c_FB = 1.0 for positions between draughts T_BAL and T_SC.
for positions above draught T_SC.

h_fb : Vertical distance, in m, from the waterline at the draught T_SC to the highest deck at side. See Figure 12.

h₀ : Vertical distance, in m, from the waterline at the draught T_SC to the considered position. See Figure 12.