3 Oil Tankers

3.1 Specific design loading conditions

3.1.1 Seagoing conditions

3.1.2 Additional loading conditions

3.2 Design load combinations for direct strength analysis

3.2.1 The design load combinations for FE analysis are given in Table 1 as follows:

3.2.2 For tankers with two oil-tight longitudinal bulkheads, where the cargo tank length is less than 0.15 L, the draughts given in Table 2, Table 4, Table 6 and Table 8 are subject to special consideration by the Society.

3.2.3 For tankers with one centreline oil-tight longitudinal bulkhead, where the cargo tank length is less than 0.11 L, the draughts given in Table 3, Table 5, Table 7 and Table 9 are subject to special consideration by the Society.

3.2.4 For seagoing conditions, the dynamic load cases required to be investigated for each loading pattern are indicated in Table 2 to Table 9. Dynamic load cases are defined in Ch 4, Sec 2.

3.2.5 Ships with structure symmetrical about centreline

For ships with structure symmetrical about the centreline, the loading pattern mirrored about centreline of another pattern may be omitted provided the results (yield and buckling) are mirrored, e.g. Table 2 A7b, A12b.

3.2.6 Tankers with two oil-tight longitudinal bulkheads except with a cross tie arrangement in the wing cargo tanks

For tankers with two oil-tight longitudinal bulkheads except with a cross tie arrangement in the wing cargo tanks, loading patterns A7 and A12 in Table 2, Table 4, Table 6 and Table 8 are to be examined for the possibility that unequal filling levels in transversely paired wing cargo tanks would result in a more onerous stress response. Loading pattern A7 is required to be analysed only if such a non-symmetric seagoing loading condition is included in the ship loading manual. The actual loading pattern, draught, GM and k_r from the loading manual are to be used in the FE analysis. Where the GM and k_r are not given in the ship’s loading manual, GM and k_r are to be determined in accordance with Ch 4, Sec 3.

If loading patterns A7 and A12 are not considered, an operational restriction describing that the difference in filling level between corresponding port and starboard wing cargo tanks is not to exceed 25% of the filling height in the wing cargo tank, is to be added in the loading manual.

Loading patterns A7 and A12 need not be examined for tankers with a cross tie arrangement in the wing cargo tanks.

3.2.7 For tankers with two oil-tight longitudinal bulkheads, seagoing loading pattern A3 and harbour loading pattern A13, with all cargo tanks abreast empty, in Table 2, Table 4, Table 6 and Table 8 are to be analysed with a ship draught of 0.65 T_SC and 0.7 T_SC respectively. If conditions in the ship loading manual specify greater draughts for loading pattern A3 or A13, then the maximum specified draught in the ship’s loading manual for the loading pattern is to be used.

3.2.8 For tankers with two oil-tight longitudinal bulkheads, seagoing loading pattern A5 and harbour loading pattern A11, with all cargo tanks abreast fully loaded, in Table 2, Table 4, Table 6 and Table 8 are to be analysed with a ship draught of 0.65 T_SC and 0.6 T_SC respectively. If conditions in the ship loading manual specify lesser draughts for loading pattern A5 or A11, then the minimum specified draught in the ship’s loading manual for the loading pattern is to be used.

3.2.9 For loading patterns A1, A2, B1, B2 and B3, with cargo tank(s) empty, in Table 2 to Table 9, a minimum ship draught of 0.9 T_SC is to be used in the analysis. If conditions in the ship loading manual specify greater draughts for loading patterns with empty cargo tank(s), then the maximum specified draught for the actual condition is to be used.

3.2.10 Ballast conditions

Where a ballast condition is specified in the ship loading manual with ballast water filled in one or more cargo tanks, loading patterns A8 or B7 in Table 2 or Table 3 are to be examined.

The actual loading pattern, draught, GM and k_r from the loading manual are to be used in the FE analysis. Where the GM and k_r are not given in the ship’s loading manual, GM and k_r are to be determined in accordance with Ch 4, Sec 3.