(a) As used in this section, Rule means the current Rules of the American Bureau of Shipping or other recognized classification society, as appropriate for the vessel's present service and regardless of the year the vessel was constructed.

(b) The requirements of this section apply to all in-service, unclassed tank vessels certificated to carry a pollution category I oil cargo listed in 46 CFR Table 30.25-1.

(c) For all vessels except those limited on their Certificate of Inspection to river routes only, the minimum midship section modulus must be—

(1) At least 90 percent of that required by Rule; or

(2) Where there is no specific Rule requirement, at least 100 percent of that which is necessary to meet the bending moment developed under a full load condition in still water, using a permissible bending stress of 12.74 kN/cm2 (1.30 t/cm2, 8.25 Ltf/in2).

(d) Within the 40-percent midship length, the average flange and web thicknesses of each longitudinal stiffener must be as follows:

(1) For deck and bottom stiffeners: at least 85 percent of Rule thickness, unless a buckling analysis demonstrates that lesser thicknesses can be safely tolerated. However, the average thickness must never be less than 80 percent of Rule thickness; and

(2) For side stiffeners: at least 75 percent of Rule thickness.

(e) Within the 40-percent midship length, the average thickness for longitudinal strength plating must be at least as follows:

(1) Weather deck: 75 percent of Rule thickness;

(2) Hatch: 70 percent of Rule thickness;

(3) Trunk: 75 percent of Rule thickness;

(4) Sheer strake: 75 percent of Rule thickness;

(5) Outer sideshell: 75 percent of Rule thickness;

(6) Inner sideshell: 75 percent of Rule thickness;

(7) Outer bottom; 75 percent of Rule thickness;

(8) Inner bottom: 70 percent of Rule thickness;

(9) Keel: 75 percent of Rule thickness;

(10) Bulkheads: 75 percent of Rule thickness.

[CGD 91-209, 58 FR 52602, Oct. 8, 1993]