Section 3 Hull girder load criteria for multi-hull craft
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Special Service Craft, July 2022 - Part 5 Design and Load Criteria - Chapter 5 Global Load and Design Criteria - Section 3 Hull girder load criteria for multi-hull craft

Section 3 Hull girder load criteria for multi-hull craft

Parent topic: Chapter 5 Global Load and Design Criteria

3.1 General

3.1.1 The vertical bending moments specified here are applicable to all multi-hull craft as defined in Pt 1, Ch 2, 2.2 Definitions 2.2.15.

3.1.2  L R and T are as defined in Pt 3, Ch 1, 6 Definitions.

3.2 Vertical wave bending moments and associated shear forces

3.2.1 The vertical wave bending moments, MMW, including wave and still water effects, at amidship is given by the following:

where
MM = S f Gf Ef CWP LS 2,5 BM kN m
CWP = the waterplane area coefficient and is to be taken not less than 0,5
Gf = service group factor, see Pt 1, Ch 2, 3.5 Service area restriction notations 3.5.5
= 0,5 for G1 craft and Zone 3 craft
= 0,6 for G2 craft and Zone 2 craft
= 0,65 for G2A craft and Zone 1 craft
= 0,7 for G3 craft
= 0,8 for G4 craft
= 1,0 for G5 and G6 craft
Sf = 1,1 for passenger and cargo craft
= 1,15 for craft other than cargo and passenger craft
Ef = 0,125 for sagging moment
= 0,2 for hogging moment
Ff = - 1,0 for sagging (negative) moment
= 1,0 for hogging (positive) moment
Df = 0 at aft end of L R
= 1,0 between 0,4L R and 0,65LR from aft end of LR
= 0 at forward end of LR
BM = total breadth of hulls or struts at LCG at the waterline, in metres, excluding tunnels
LS = Rule length, LR, in metres, for partially submerged hulls
= strut length, in metres, for fully submerged hulls

3.2.2 The wave shear force, QMW, at any position along the craft is given by:

where MM is as defined in Pt 5, Ch 5, 3.2 Vertical wave bending moments and associated shear forces 3.2.1 and Kf is as defined in Pt 5, Ch 5, 2.4 Wave shear force 2.4.1.

3.3 Dynamic bending moments

3.3.1 The dynamic bending moments, including wave and still water effects, specified here are applicable to all non-displacement multi-hull craft as defined in Pt 1, Ch 2, 2.2 Definitions 2.2.15.

3.3.2 The dynamic bending moment, M MDW, due to slamming effects at amidships is to be calculated using the following expression:

where
M MD = 52 Δ L S(20 a v - 5) x 10-3 kNm
F f = - 1,0 for sagging (negative) moment
= 1,0 for hogging (positive) moment
D f = 0 at aft end of L R
= 1,0 between 0,4L R and 0,65L R from aft
= 0 at forward end of L R
a v = vertical acceleration at the LCG, in terms of g, as defined in Pt 5, Ch 2, 3.2 Vertical acceleration 3.2.5 as appropriate, see also Pt 5, Ch 5, 1.1 Introduction 1.1.6
Δ = displacement, in tonnes, as defined in Pt 5, Ch 2, 2.2 Symbols 2.2.2

L S is as defined in Pt 5, Ch 5, 3.2 Vertical wave bending moments and associated shear forces 3.2.1.

3.3.3 The bottom longitudinals amidships are additionally subjected to the following effective pressure, P s:

where

P dl is as defined in Pt 5, Ch 2, 5.2 Impact pressure for non-displacement mode 5.2.1. T is as defined in Pt 3, Ch 1, 6 Definitions.

3.3.4 The bottom plating amidships is subjected to the following additional effective pressure, P t:

where

P dl is as defined in Pt 5, Ch 2, 5.2 Impact pressure for non-displacement mode 5.2.1. T is as defined in Pt 3, Ch 1, 6 Definitions

3.3.5 The dynamic shear force, Q MDW, at any position along the craft is given by:

where M MD is as defined in Pt 5, Ch 5, 3.3 Dynamic bending moments 3.3.2. and K f as defined in Pt 5, Ch 5, 2.4 Wave shear force 2.4.1.

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