4.5 Offshore supply vessels

• .1 The provisions given hereunder apply to offshore supply vessels, as defined in 1.3.6, of 24 m in length and over. The alternative stability criteria contained in 4.5.6 apply to vessels of not more than 100 m in length.

• .2 For a vessel engaged in near-coastal voyages, as defined in 4.5.2, the principles given in 4.5.3 should guide the Administration in the development of its national standards. Relaxations from the requirements of the Code may be permitted by an Administration for vessels engaged in near-coastal voyages off its own coasts provided the operating conditions are, in the opinion of that Administration, such as to render compliance with the provisions of the Code unreasonable or unnecessary.

• .3 Where a ship other than an offshore supply vessel, as defined in 1.3.6, is employed on a similar service, the Administration should determine the extent to which compliance with the provisions of the Code is required.

  Near-coastal voyage means a voyage in the vicinity of the coast of a State as defined by the Administration of that State.

• .1 The Administration defining near-coastal voyages for the purpose of the present Code should not impose design and construction standards for a vessel entitled to fly the flag of another State and engaged in such voyages in a manner resulting in a more stringent standard for such a vessel than for a vessel entitled to fly its own flag. In no case should the Administration impose, in respect of a vessel entitled to fly the flag of another State, standards in excess of the Code for a vessel not engaged in near-coastal voyages.

• .2 With respect to a vessel regularly engaged in near-coastal voyages off the coast of another State the Administration should prescribe design and construction standards for such a vessel at least equal to those prescribed by the Government of the State off whose coast the vessel is engaged, provided such standards do not exceed the Code in respect of a vessel not engaged in near-coastal voyages.

• .3 A vessel which extends its voyages beyond a near-coastal voyage should comply with the present Code.

• .1 Access to the machinery space should, if possible, be arranged within the forecastle. Any access to the machinery space from the exposed cargo deck should be provided with two weathertight closures. Access to spaces below the exposed cargo deck should preferably be from a position within or above the superstructure deck.

• .2 The area of freeing ports in the side bulwarks of the cargo deck should at least meet the requirements of regulation 27 of the International Convention on Load Lines, 1966. The disposition of the freeing ports should be carefully considered to ensure the most effective drainage of water trapped in pipe deck cargoes or in recesses at the after end of the forecastle. In vessels operating in areas where icing is likely to occur, no shutters should be fitted in the freeing ports.

• .3 The Administration should give special attention to adequate drainage of pipe stowage positions having regard to the individual characteristics of the vessel. However, the area provided for drainage of the pipe stowage positions should be in excess of the required freeing port area in the cargo deck bulwarks and should not be fitted with shutters.

• .4 A vessel engaged in towing operations should be provided with means for quick release of the towing hawser.

• .1 The arrangement of cargo stowed on deck should be such as to avoid any obstruction of the freeing ports or of the areas necessary for the drainage of pipe stowage positions to the freeing ports.

• .2 A minimum freeboard at the stern of at least 0.005 L should be maintained in all operating conditions.

• .1 The stability criteria given in 3.1.2 should apply to all offshore supply vessels except those having characteristics which render compliance with 3.1.2 impracticable.

• .2 The following equivalent criteria are recommended where a vessel's characteristics render compliance with 3.1.2 impracticable:

  • .2.1 The area under the curve of righting levers (GZ curve) should not be less than 0.070 metre-radians up to an angle of 15° when the maximum righting lever (GZ) occurs at 15° and 0.055 metre-radians up to an angle of 30° when the maximum righting lever (GZ) occurs at 30° or above. Where the maximum righting lever (GZ) occurs at angles of between 15° and 30°, the corresponding area under the righting lever curve should be:

    0.055 + 0.001 (30° - θ_max) metre-radians ^footnote

  • .2.2 The area under the righting lever curve (GZ curve) between the angles of heel of 30° and 40°, or between 30° and O_f if this angle is less than 40°, should be not less than 0.03 metre-radians.

  • .2.3 The righting lever (GZ) should be at least 0.20 m at an angle of heel equal to or greater than 30°.

  • .2.4 The maximum righting lever (GZ) should occur at an angle of heel not less than 15°.

  • .2.5 The initial transverse metacentric height (GM_o) should not be less than 0.15 m.

• .3 Reference is made also to recommendations contained in section 2.3 and paragraphs 3.1.2.7 to 3.1.2.9.

 The standard loading conditions should be as follows:

• .1 Vessel in fully loaded departure condition with cargo distributed below deck and with cargo specified by position and weight on deck, with full stores and fuel, corresponding to the worst service condition in which all the relevant stability criteria are met.

• .2 Vessel in fully loaded arrival condition with cargo as specified in .1, but with 10% stores and fuel.

• .3 Vessel in ballast departure condition, without cargo but with full stores and fuel.

• .4 Vessel in ballast arrival condition, without cargo and with 10% stores and fuel remaining.

• .5 Vessel in the worst anticipated operating condition.

 The assumptions for calculating loading conditions should be as follows:

• .1 If a vessel is fitted with cargo tanks, the fully loaded conditions of 4.5.7.1 and 4.5.7.2 should be modified, assuming first the cargo tanks full and then the cargo tanks empty.

• .2 If in any loading condition water ballast is necessary, additional diagrams should be calculated, taking into account the water ballast, the quantity and disposition of which should be stated in the stability information.

• .3 In all cases when deck cargo is carried a realistic stowage weight should be assumed and stated in the stability information, including the height of the cargo and its centre of gravity.

• .4 Where pipes are carried on deck, a quantity of trapped water equal to a certain percentage of the net volume of the pipe deck cargo should be assumed in and around the pipes. The net volume should be taken as the internal volume of the pipes, plus the volume between the pipes. This percentage should be 30 if the freeboard amidships is equal to or less than 0.015 L and 10 if the freeboard amidships is equal to or greater than 0.03 L. For intermediate values of the freeboard amidships the percentage may be obtained by linear interpolation. In assessing the quantity of trapped water, the Administration may take into account positive or negative sheer aft, actual trim and area of operation.

• .5 If a vessel operates in zones where ice accretion is likely to occur, allowance for icing should be made in accordance with the provisions of chapter 5.