Section 14 Direct calculation

14.1.1 For container ships as defined in Pt 4, Ch 8, 1.3 Class notations 1.3.3, longitudinal strength calculations are to be made in accordance with Parts A and B of LR’s ShipRight SDA Procedure for container ships, see also Table 8.14.1 Summary of direct calculation analysis requirements for container ships

14.1.2 The global, primary and local structure scantlings are to be assessed using the vertical and horizontal wave bending moments and shear forces and torsional wave moments derived using non-linear ship motion analysis based on equivalent design sea state methods where one or more of the following conditions applies:

1. B > 60 m

2. L > 425 m

The methodology to calculate the non-linear ship motion wave loads is given in LR’s ShipRight Procedure Guidance Notes on the Assessment of Global Design Loads of Large Container Ships and Other Ships Prone to Whipping and Springing.

14.2.1 For container ships as defined in Pt 4, Ch 8, 1.3 Class notations 1.3.3, the strength of the ship’s primary structure scantlings of double bottom, side and transverse bulkheads is to be assessed in accordance with Part C of LR’s ShipRight SDA Procedure for container ships. The vertical wave bending moments are to be calculated in accordance with Pt 4, Ch 8, 16.6 Design vertical wave bending moments. All other hull girder loads are to be calculated in accordance with Pt 4, Ch 8, 3.3 Combined longitudinal and torsional strength.

14.2.2 For other container ships the method for analysis of primary structure of double bottom, side structure and transverse bulkheads is to be agreed with LR.

14.3.1 The ShipRight notations WDA 1 and WDA2 are mandatory for container ships as indicated in Table 8.14.1 Summary of direct calculation analysis requirements for container ships, and where the ultimate strength of the hull girder is assessed against the extreme wave bending moments including whipping and wave impact loads, in accordance with LR’s ShipRight Procedure Global Design Loads of Container Ships and Other Ships Prone to Whipping and Springing:

Table 8.14.1 Summary of direct calculation analysis requirements for container ships

			Application criteria. If any of the following criteria apply then the appropriate analysis is required
Rule requirement See Note 1	Rule reference	ShipRight notation
			Length criteria	Any of |ffS| > 1,55 or fbow> 1,85	f c > f sp	Deck or hatch side coaming steel grade ≥ HT47	Bottom steel grade ≥ HT36 See Note 5	Breadth criteria
LR’s ShipRight SDA Procedure for container ships	Pt 4, Ch 8, 1.3 Class notations 1.3.3	SDA	L > 150	—	—	—	—	B > 32,26
Non-linear ship motion analysis to calculate combined vertical, horizontal and torsional loads	Pt 4, Ch 8, 14.1 Procedures for calculation of combined longitudinal and torsional strength 14.1.2	—	L > 425	—	—	—	—	B > 60
Fatigue assessment	Pt 4, Ch 8, 14.3 Procedures for verification of structural response due to whipping, springing and fatigue 14.3.2	FDA (see Note 3)	L > 350	—	L > 250	Yes	Yes	—
Whipping assessment Level 1 See Note 4	Pt 4, Ch 8, 14.3 Procedures for verification of structural response due to whipping, springing and fatigue 14.3.1	WDA1	—	—	—	—	—	B > 32,26
Whipping assessment Level 2 See Note 4	Pt 4, Ch 8, 14.3 Procedures for verification of structural response due to whipping, springing and fatigue 14.3.1	WDA2	L > 350	L > 275	—	Yes	Yes	—
Springing assessment See Note 2	Pt 4, Ch 8, 14.3 Procedures for verification of structural response due to whipping, springing and fatigue 14.3.2	FDA SPR	L > 350	—	L > 250	Yes	Yes	—
Symbols and definitions
ffS is defined in Pt 4, Ch 8, 16.6 Design vertical wave bending moments 16.6.1
fbow is defined in Pt 4, Ch 8, 16.6 Design vertical wave bending moments 16.6.3
fc is a wave encounter frequency at which it is expected that springing will become important
fsp is the natural frequency of the 2 node hull girder vertical bending mode in Hz. This can be very approximately calculated as:
V = speed in knots as defined in Pt 3, Ch 1, 6.1 Principal particulars 6.1.10
E = Young’s modulus in N/mm2 = 206000 N/mm2 for steel
Inet = net midship moment of inertia in m4, see Pt 3, Ch 4 Longitudinal Strength
Td = design (normal standard operating) draught, in metres
Cb1 = moulded block coefficient at draught Td, based on Rule length, L, and moulded breadth, B
and B are given in Pt 3, Ch 1, 6 Definitions.
Note 1 The stated rule requirements may be deemed applicable to ships that do not meet the application criteria but where the structural configuration is such as to necessitate them. Note 2 The results of the springing assessment may also need a fatigue assessment procedure to be undertaken. Note 3 If ShipRight notation FDA is to be assigned, the requirements of LR’s ShipRight FDA procedure are to be complied with; this may require calculations additional to those implied by Pt 4, Ch 8, 14.3 Procedures for verification of structural response due to whipping, springing and fatigue 14.3.2. Note 4 A Level 2 Whipping Assessment may be carried out instead of a Level 1 Whipping Assessment at the Owner’s request. Where a level 2 Whipping Assessment is undertaken, a Level 1 Whipping Assessment need not be carried out. Note 5 This is applicable only when a bottom steel grade greater than or equal to HT36 is needed to satisfy the requirements of Pt 4, Ch 8, 16 Longitudinal strength calculations.

14.3.2 The ShipRight notation FDA SPR is mandatory for container ships as indicated in Table 8.14.1 Summary of direct calculation analysis requirements for container ships, and where the fatigue performance of the hull girder taking into account the effects from springing, is assessed in accordance with LR’s ShipRight Procedure Global Design Loads of Container Ship and Other Ships Prone to Whipping and Springing, which also makes reference to LR’s ShipRight FDA procedures.