Section 4 Shell envelope plating

4.1.1 On ships over 50 m in length, where there is a centreline well, or where hopper doors are fitted on the ship's centreline, i.e. where no centreline box keel is fitted in a hopper, a keel strake is to be fitted on each side of the well or hopper door opening, dependent upon the proposed docking arrangements for the ship. The width of each keel strake is to be not less than half that required for a centreline keel nor less than 400 mm. The thickness of each keel strake is to be not less than the thickness required for a centreline keel in Pt 4, Ch 1, 5.2 Keel.

4.2.1 The minimum thickness of bottom shell plating amidships on hopper dredgers and hopper barges classed for unrestricted service is to be 15 per cent greater than that required by Pt 4, Ch 1, 5.3 Bottom shell and bilge. The thickness of bottom shell plating on ships classed A1 protected waters service is to be not less than:

or that required for Pt 4, Ch 1, 5.3 Bottom shell and bilge, whichever is the lesser, but with an overall minimum thickness of 6 mm.

4.2.2 Where hoppers extend outside 0,4L amidships, the thicknesses required for the bottom shell amidships are to be maintained for at least two frame spaces beyond the ends of the hoppers before being tapered to the end thicknesses.

4.3.1 For ships intended to operate aground, see Pt 4, Ch 12, 7 Bottom strengthening for operating aground.

4.4.1 The corners of hopper door openings and of bucket and ladder wells are generally to be parabolic or elliptical on all ships where L is greater than 50 m, and should generally be rounded on smaller ships. On ships where L is greater than 90 m, the arrangement of hopper and well corners within 0,5L amidships should generally be as required for deck hatch corners. The sealing arrangements for hopper doors may lie within the line of the corners, provided that the construction is such as to avoid high stress concentrations in the structure.

4.5.1 On ships arranged with two chines each side, the bilge plating should generally be calculated from the bottom plating formulae. On hard chine ships, flanged chines will not generally be approved, but where a chine is formed by knuckling the shell plating, the radius of curvature, measured on the inside of the plate, is to be not less than 10 times the plate thickness. Where a solid round chine bar is fitted, the bar diameter is to be not less than 50 mm or three times the thickness of the thickest abutting plate, whichever is the greater. Where welded chines are used, the welding is to be built up as necessary to ensure that the shell plating thickness is maintained across the weld.

4.6.1 The thickness of the side shell is to be in accordance with Pt 4, Ch 1, 5.4 Side shell. On ships classed A1 protected waters service the thickness of the side shell throughout, including at ends, may be reduced by 20 per cent from that required by Pt 4, Ch 1, 5.4 Side shell and Pt 3, Ch 5 Fore End Structure and Pt 3, Ch 6 Aft End Structure as appropriate, provided that the combined shear stress does not exceed 110 N/mm².

4.6.2 Where high compressive loads occur in the sheerstrake, the thickness may be required to be increased to minimise the likelihood of buckling.

4.7.1 The plating of swim ends is to have a thickness not less than that required for the bottom shell up to the waterline at draught T, see also Table 12.7.1 Bottom strengthening for operating aground. It is to have a thickness not less than that required for side shell in the areas more than 1,0 m above the waterline at draught T _m. In intermediate areas the thickness may be tapered from the bottom to the side shell requirements.