Section 3 Motion response
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 2 Local Design Loads - Section 3 Motion response

Section 3 Motion response

Parent topic: Chapter 2 Local Design Loads

3.1 Relative vertical motion

3.1.1 The relative vertical motion is to be taken as:

where
k r = see Table 2.3.1 Hull form wave pressure factor
C w,min =
k m =
x m = 0,45 – 0,6F n but not less than 0,2
C w = wave head, in metres
=
x wI = distance from aft end of L WL, in metres, see Pt 5, Ch 2, 2.2 Symbols 2.2.1
L WL = waterline length, in metres, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.19
C b = block coefficient, see Pt 5, Ch 2, 2.2 Symbols
F n = Froude Number, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.7, where V m = 2/3V
V = as defined in Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.2.

Table 2.3.1 Hull form wave pressure factor

Craft type k r
Mono-hull craft in the non-displacement mode 2,25
Mono-hull craft in the displacement mode 1,95
Catamarans and multi-hull craft with partially submerged hulls 2,55
Swaths and multi-hull craft with fully submerged hulls 2,10
Craft supported by hydrodynamic lift provided by foils or other lifting devices 1,50

Note Where multiple craft types apply, the higher value of k r is to be used.

3.2 Vertical acceleration

3.2.1 The instantaneous accelerations determined in accordance with the formulae in this Section are to be used to estimate the relationship between allowable speed, V, in knots, wave height, H 1/3, in metres, and displacement, Δ, in tonnes, and they will form the operational envelope.

3.2.2 Where the Taylor Quotient, Γ, is greater than 10,8, the motion response criteria are to be specially considered.

3.2.3 The vertical acceleration at the LCG (longitudinal centre of gravity), a v, is defined as the average of the 1/100 highest accelerations at the LCG.

3.2.4 The vertical acceleration in the non-displacement mode for mono-hull craft is to be taken as:

where
= a v is the vertical acceleration at the LCG in terms of g
Γ = Taylor Quotient, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.17
g = acceleration due to gravity (9,81 m/sec2)
L 1 = , but is not to be taken as less than 3
H 1 = , but is not to be taken as less than 0,2
B c = breadth of hull between the chines or bilge tangential points at LCG, as appropriate, in metres
B W = breadth of hull at the LCG measured at the waterline, in metres
Δ = displacement, in tonnes, as defined in Pt 5, Ch 2, 2.2 Symbols 2.2.2
H 1/3 = design significant wave height in metres
θD = deadrise angle at the LCG, in degrees, but is not to be taken as greater than 30o
θB = running trim angle in degrees, but is not to be taken as less than 3o
L WL = waterline length, in metres, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.19

3.2.5 The vertical acceleration in the non-displacement mode for multi-hull craft is to be taken as:

where
= a v is the vertical acceleration at the LCG in terms of g.
Γ = Taylor Quotient, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.17
fa = hull form acceleration factor
= 2,7 for craft supported mainly by hydrodynamic lift provided by foils or other lifting devices
= 3,6 for Swaths and multi-hull craft with fully submerged hulls
= 4,5 for catamarans and multi-hull craft with partially submerged hulls
B M = total breadth of hulls or struts at LCG at the waterline, in metres, excluding tunnels
Δ = displacement, in tonnes.
H 1/3 = design significant wave height, in metres
θD = deadrise angle at the LCG, in degrees, but is not to be taken as greater than 30o, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.5
L WL = waterline length, in metres, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.19

3.2.6 The vertical acceleration in the displacement mode for all craft is to be taken as:

where
= a v is the vertical acceleration at the LCG in terms of g
L WL = waterline length, in metres, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.19
Γ = Taylor's Quotient, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.17

3.2.7 The vertical acceleration, a x, at any given location distance x a from the AP along the hull may be taken as:

where
a v = vertical acceleration at LCG in terms of g, as appropriate.
a x = is the vertical acceleration at distance x a from AP on the static load waterline, in terms of g
x a = distance from aft end of the static load waterline, in metres, to the point at which the vertical acceleration is calculated
x LCG = distance from aft end of the static load waterline, in metres, to the LCG
L WL = waterline length, in metres, see Pt 5, Ch 2, 2.1 Parameters to be used for the determination of load and design criteria 2.1.19
ξa = .
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