§ 157.10d Double hulls on tank vessels.

(a) With the exceptions stated in § 157.08(n), this section applies to a tank vessel—

(1) For which the building contract is awarded after June 30, 1990;

(2) That is delivered after December 31, 1993;

(3) That undergoes a major conversion for which;

(i) The contract is awarded after June 30, 1990; or

(ii) Conversion is completed after December 31, 1993; or

(4) That is otherwise required to have a double hull by 46 U.S.C. 3703a(c).

(b) Each vessel to which this section applies must be fitted with:

(1) A double hull in accordance with this section; and

(2) If § 157.10 applies, segregated ballast tanks and a crude oil washing system in accordance with that section.

(c) Except on a vessel to which § 157.10d(d) applies, tanks within the cargo tank length that carry any oil must be protected by double sides and a double bottom as follows:

(1) Double sides must extend for the full depth of the vessel's side or from the uppermost deck, disregarding a rounded gunwale where fitted, to the top of the double bottom. At any cross section, the molded width of the double side, measured at right angles to the side shell plating, from the side of tanks containing oil to the side shell plating, must not be less than the distance w as shown in Figure 157.10d(c) and specified as follows:

(i) For a vessel of 5,000 DWT and above: w = [0.5 + (DWT/20,000)] meters; or, w = 2.0 meters (79 in.), whichever is less, but in no case less than 1.0 meter (39 in.).

(ii) For a vessel of less than 5,000 DWT: w = [0.4 + (2.4)(DWT/20,000)] meters, but in no case less than 0.76 meter (30 in.).

(iii) For a vessel to which paragraph (a)(4) of this section applies: w = 0.76 meter (30 in.), provided that the double side was fitted under a construction or conversion contract awarded prior to June 30, 1990.

(2) At any cross section, the molded depth of the double bottom, measured at right angles to the bottom shell plating, from the bottom of tanks containing oil to the bottom shell plating, must not be less than the distance h as shown in Figure 157.10d(c) and specified as follows:

(i) For a vessel of 5,000 DWT and above: h = B/15; or, h = 2.0 meters (79 in.), whichever is less, but in no case less than 1.0 meter (39 in.).

(ii) For a vessel of less than 5,000 DWT: h = B/15, but in no case less than 0.76 meter (30 in.).

(iii) For a vessel to which paragraph (a)(4) of this section applies: h = B/15; or, h = 2.0 meters (79 in.), whichever is the lesser, but in no case less than 0.76 meter (30 in.), provided that the double bottom was fitted under a construction or conversion contract awarded prior to June 30, 1990.

(3) For a vessel built under a contract awarded after September 11, 1992, within the turn of the bilge or at cross sections where the turn of the bilge is not clearly defined, tanks containing oil must be located inboard of the outer shell—

(i) For a vessel of 5,000 DWT and above: At levels up to 1.5h above the base line, not less than the distance h, as shown in Figure 157.10d(c) and specified in paragraph (c)(2) of this section. At levels greater than 1.5h above the base line, not less than the distance w, as shown in Figure 157.10d(c) and specified in paragraph (c)(1) of this section.

(ii) For a vessel of less than 5,000 DWT: Not less than the distance h above the line of the mid-ship flat bottom, as shown in Figure 157.10d(c)(3)(ii) and specified in paragraph (c)(2) of this section. At levels greater than h above the line of the mid-ship flat bottom, not less than the distance w, as shown in Figure 157.10d(c)(3)(ii) and specified in paragraph (c)(1) of this section.

(4) For a vessel to which § 157.10(b) applies that is built under a contract awarded after September 11, 1992.

(i) The aggregate volume of the double sides, double bottom, forepeak tanks, and afterpeak tanks must not be less than the capacity of segregated ballast tanks required under § 157.10(b). Segregated ballast tanks that may be provided in addition to those required under § 157.10(b) may be located anywhere within the vessel.

(ii) Double side and double bottom tanks used to meet the requirements of § 157.10(b) must be located as uniformly as practicable along the cargo tank length. Large inboard extensions of individual double side and double bottom tanks, which result in a reduction of overall side or bottom protection, must be avoided.

(d) A vessel of less than 10,000 DWT that is constructed and certificated for service exclusively on inland or limited short protected coastwise routes must be fitted with double sides and a double bottom as follows:

(1) A minimum of 61 cm. (2 ft.) from the inboard side of the side shell plate, extending the full depth of the side or from the main deck to the top of the double bottom, measured at right angles to the side shell; and

(2) A minimum of 61 cm. (2 ft.) from the top of the bottom shell plating, along the full breadth of the vessel's bottom, measured at right angles to the bottom shell.

(3) For a vessel to which paragraph (a)(4) of this section applies, the width of the double sides and the depth of the double bottom may be 38 cm. (15 in.), in lieu of the dimensions specified in paragraphs (d)(1) and (d)(2) of this section, provided that the double side and double bottom tanks were fitted under a construction or conversion contract awarded prior to June 30, 1990.

(4) For a vessel built under a contract awarded after September 11, 1992, a minimum 46 cm. (18 in.) clearance for passage between framing must be maintained throughout the double sides and double bottom.

(e) Except as provided in paragraph (e)(3) of this section, a vessel must not carry any oil in any tank extending forward of:

(1) The collision bulkhead; or

(2) In the absence of a collision bulkhead, the transverse plane perpendicular to the centerline through a point located:

(i) The lesser of 10 meters (32.8 ft.) or 5 percent of the vessel length, but in no case less than 1 meter (39 in.), aft of the forward perpendicular;

(ii) On a vessel of less than 10,000 DWT tons that is constructed and certificated for service exclusively on inland or limited short protected coastwise routes, the lesser of 7.62 meters (25 ft.) or 5 percent of the vessel length, but in no case less than 61 cm. (2 ft.), aft of the headlog or stem at the freeboard deck; or

(iii) On each vessel which operates exclusively as a box or trail barge, 61 cm. (2 ft.) aft of the headlog.

(3) This paragraph does not apply to independent fuel oil tanks that must be located on or above the main deck within the areas described in paragraphs (e)(1) and (e)(2) of this section to serve adjacent deck equipment that cannot be located further aft. Such tanks must be as small and as far aft as is practicable.

(f) On each vessel, the cargo tank length must not extend aft to any point closer to the stern than the distance equal to the required width of the double side, as prescribed in § 157.10d(c)(1) or § 157.10d(d)(1).

[CGD 90–051, 57 FR 36239, Aug. 12, 1992, as amended by USCG–1999–6164, 65 FR 39262, June 23, 2000]