Section 1 General

1.1.1 The requirements of this Chapter are applicable to multi-hull craft of steel construction as defined in Ch 1, 1 Background.

1.2.1 Except as otherwise specified within this Chapter, the scantlings and arrangements of multi-hull craft are to be determined in accordance with the procedures described in, or required by Pt 6, Ch 3 Scantling Determination for Mono-Hull Craft for mono-hull craft, using the pressures from Pt 5 Design and Load Criteria appropriate to multi-hulls.

1.3.1 Where the craft is of unusual design, form or proportions, or where the speed of the craft exceeds 60 knots the scantlings are to be determined by direct calculation.

1.3.2 The requirements of this Chapter may be modified where direct calculation procedures are adopted to analyse the stress distribution in the primary structure.

1.4.1 Clasifications Register (hereinafter referred to as 'LR') will consider direct calculations for the derivation of scantlings as an alternative and equivalent to those derived by Rule requirements in accordance with Pt 3, Ch 1, 3 Equivalents.

1.5.1 The symbols used in this Chapter are defined below and in the appropriate Section:

1.5.2  Bottom outboard. For high speed craft, where the scantlings of the bottom shell are governed by impact pressure considerations, the bottom outboard shell is defined as the area of the hull between the outboard edge of the keel and the outer bilge tangential point. For displacement and semi displacement type craft where the scantlings of the bottom shell are governed by either hydrostatic or pitching pressures the bottom outboard shell is to extend to the chine line or 150 mm above the static load waterline, whichever is the greater.

1.5.3  Bottom inboard. For high speed craft, where the scantlings of the bottom shell are governed by impact pressure considerations, the bottom inboard shell is defined as the area of the hull between the inboard edge of the keel and the inner bilge tangential point. For displacement and semi displacement type craft where the scantlings of the bottom shell are governed by either hydrostatic or pitching pressures the bottom inboard shell is to extend to the chine line or 150 mm above the static load waterline, whichever is the greater.

1.5.4  Cross-deck. The cross-deck is defined as the structure which forms the bridge connection between any two adjacent hulls.

1.5.5  Haunch. The haunch is defined as the transition area between the cross-deck and the inboard side shell plating.

1.5.6  Side inboard. The side inboard is defined as the area between the bottom inboard shell and the wet-deck (or lower edge of the haunches, where fitted).

1.5.7  Side outboard. The side outboard is defined as the area between bottom outboard shell and the deck at side.

1.5.8  Wet-deck. The wet-deck is defined as the area between the upper edges of the side inboard plating (or upper edges of the haunches, where fitted).