Section 11 Launch and recovery, berthing and dry-docking arrangements

11.1.1 To resist loads imposed by tugs and berthing operations all structure within a 1,0 m strip centred 1,0 m above the deep waterline. It should be able to withstand the following pressure P _b:

=

11.1.2 If L _R >200 m, or the ship is able to have significantly different loading conditions, the strip is to be taken from 1,5 m above the light waterline to 2,5 m above the deep waterline.

11.1.3 Ships with markings to indicate location of internal structure designed specifically for berthing purposes will be specially considered.

11.2.1 Dry-docking arrangements are not explicitly covered in the Rules, see Vol 1, Pt 3, Ch 1, 4.1 Submission of plans and data. These requirements are intended to address the loads imposed on the vessel during dry-docking.

11.3.1 In accordance with Vol 1, Pt 6, Ch 1, 2.2 Plans to be submitted 2.2.6 a dry-docking plan is to be submitted as a supporting document. Consideration should be given throughout the design of a vessel to producing a dry-docking plan. The dry-docking plan should include, but not be limited to, the following information:

• The permissible locations of dock furniture;
• Maintenance and withdrawal envelopes;
• The arrangement of underwater fittings and openings.

The dry-docking plan should take into account multiple likely docking arrangements for maintenance and through-life support.

11.4.1 Dry-docking a ship on blocks potentially imposes high vertical loads on the keel. For ships where the Rule length, L _R, exceeds 50 m, the strength of the keel and bottom structure is to be assessed.

11.4.2 Methods, other than those described here, for demonstrating that the strength of the keel and bottom structure is sufficient to withstand the loads imposed by dry-docking may be considered. Such methods are to be agreed with LR prior to the analysis being conducted.

11.4.3 For each dry-docking arrangement the stress and buckling behaviour of the bottom structure in way of the proposed dock blocks is to be assessed. The acceptance criteria given in Table 5.11.1 Acceptance criteria are not to be exceeded.

Table 5.11.1 Acceptance criteria

Structural Item	Allowable stresses, see Note		Minimum Buckling factor
	σe	τ	λ
Double bottom girders	0,75 σL	0,35 σo	1,2
Double bottom floors	0,75 σL	0,35 σo	1,1
Symbols
σo = specified minimum yield stress of material. σo for steels having a yield stress above 355 N/mm2 will be specially considered σL = λ = factor against elastic buckling σe =
Note In areas where the openings have not been modelled, the resulting shear stress and Von Mises stress is to be corrected according to the ratio of the actual to the modelled shear area. If the resulting stress levels exceed 90% of the specified allowable values, further study by means of fine mesh follow up models may be required. Von Mises stresses are to be recalculated on the basis of the corrected shear stresses.

11.4.4 Where it is anticipated that there will be more than one typical dry-docking loading condition, the bottom structure is to be assessed for a representative number of loading conditions.

11.4.5 It is recommended that the block load distribution be derived by direct calculation using a full ship finite element model, constructed generally in accordance with the ShipRight SDA procedure for passenger ships. Where the dry-docking load distribution, F _DL, as defined in Vol 1, Pt 3, Ch 5, 11.4 Dry-docking loads 11.4.6 becomes negative at any point, the block load distribution is to be derived by such direct calculations. The model is to be supported on grounded spring elements representing the proposed dry-docking arrangements. The spring element stiffness in the model should be representative of the combined block and capping stiffness. A sensitivity assessment should be carried out to ascertain the structural response to the spring constant used.

11.4.6 The following equation may be used to calculate the dry-docking load distribution, F _DL, between main transverse bulkheads acting on a keel block:

11.4.7 For ships with an after end cut-up or significant rake of stem where there is considerable overhang, it may be assumed that the increase in load due to the overhang will extend a distance equal to twice the length of the overhang and will be distributed parabolically, see Figure 5.11.1 Calculation of dock block loads in way of the after cut-up.

Figure 5.11.1 Calculation of dock block loads in way of the after cut-up

11.4.8 The increase in weight per unit length to be added due to an overhang, see Vol 1, Pt 3, Ch 5, 11.4 Dry-docking loads 11.4.6, is to be determined from the following equation:

	=	where
W oh	=	additional weight per unit length due to overhang, in kN/m
W o	=	weight of overhang in kN
k dl	=
x	=	distance from the overhang, measured in metres from the mid-point of the last keel block
L o	=	length of overhang, in metres
L G	=	horizontal distance measured from the mid-point of the last keel block to the centre of gravity of the overhang, in metres.

11.4.9 When an overlap of the forward and aft overhang correction curves occurs, both curves are to be included. This will increase the possibility that blocks amidships will become unloaded, see Vol 1, Pt 3, Ch 5, 11.4 Dry-docking loads 11.4.5.

11.5.1 The launching loads are to be checked by the shipbuilder using conventional analytical methods appropriate to the method of launch. If via a slipway, the structure in way of the fore poppet should be suitable for the high loads that will be transmitted in this area. If adequate structure is not available, temporary stiffening is to be arranged.

11.5.2 The global strength of the hull girder is to be adequate under the loads imposed by launching, in particular for NS1 ships.