Section 9 Subdivision structure on vehicle deck

9.1 General

9.1.1 The requirements of this Section cover subdivision structure fitted on the vehicle deck(s) of roll on-roll off passenger ships. Subdivision structure includes partition doors, bulkheads and longitudinal casings.

9.1.2 Where a ship is provided with subdivision structure that complies with the requirements of this Section, the ship will be eligible to be assigned the descriptive note SSDS which will be entered in column 6 of the Register Book.

9.1.3 The fitting of subdivision structure on the vehicle deck(s) forms one option to mitigate the stability-reducing effects of water on the vehicle deck(s) after damage. Such measures may be required by the National Administration with whom the ship is registered and/or by the National Administration within whose territorial jurisdiction the ship is intended to operate, for example see The Stockholm Agreement.

9.2 Design loads

9.2.1 For calculation of the design loads, an equivalent depth of water on the first vehicle deck above the design waterline, d, in metres, is to be derived in accordance with the requirements of the National Administration, see Pt 4, Ch 2, 9.1 General 9.1.3

9.2.2 It is assumed that vehicles and cargo are effectively lashed and secured to prevent movement from the stowed position.

9.2.3 The design heads (see Figure 2.9.1 Design heads for different locations in compartment) are not to be taken less than the greater of 0,5 m and:

For transverse structure more than 1,5 m away from the longitudinal boundaries of the compartment:

Symbols are as defined in Pt 4, Ch 2, 9.2 Design loads 9.2.4.
For longitudinal structure more than L _c/6 away from the transverse boundaries of the compartment:

Symbols are as defined in Pt 4, Ch 2, 9.2 Design loads 9.2.4.
For structure elsewhere:

Symbols are as defined in Pt 4, Ch 2, 9.2 Design loads 9.2.4.

Figure 2.9.1 Design heads for different locations in compartment

9.2.4 Symbols, as used in Pt 4, Ch 2, 9.2 Design loads 9.2.3, are defined as follows:

equivalent depth of water on the vehicle deck, in metres, in the upright condition taking into account the volume of flooded and accumulated water on the vehicle deck calculated in accordance with the requirements of the National Administration, see Pt 4, Ch 2, 9.1 General 9.1.3 and Pt 4, Ch 2, 9.2 Design loads 9.2.1

vertical distance, between the point under consideration and the flooded vehicle deck, in metres. For plate panels the point under consideration is to be taken as one third of the panel height above its lower edge. For stiffeners the point under consideration is to be taken as the midspan of the effective length

B _c

breadth of compartment, in metres, see Figure 2.9.1 Design heads for different locations in compartment

0,21 e(^-0,0033L_pp) and need not exceed 0,14

L _c

length of compartment, in metres, see Figure 2.9.1 Design heads for different locations in compartment

B _c d -

and is not to be taken less than 0

base of natural logarithms, 2,7183

L _pp

as defined in Pt 3, Ch 1, 6 Definitions

9.2.5 The design heads calculated in Pt 4, Ch 2, 9.2 Design loads 9.2.3 are based on the ship being in the upright condition. Where the actual damaged floating position is specified, the design heads will be specially considered taking this into account.

9.2.6 The subdivision structure, and access doors within the subdivision structure, are to be capable of withstanding the design loading applied from the side of the compartment under consideration.

9.2.7 Consideration will be given to the use of design heads agreed by the National Administration.

9.3 Height of subdivision structure

9.3.1 The height of the subdivision structure, H _D, is not to be less than:

4m, or
8d, but not less than 2,2 m, or
the height between the vehicle deck under consideration and the underside of the next watertight deck above,

whichever is the lesser.

where

is defined in Pt 4, Ch 2, 9.2 Design loads 9.2.4.

9.3.2 For special arrangements, such as hanging car decks or wide side casings, other subdivision structure heights may be accepted on the basis of detailed model tests in the flooded conditions under investigation by the National Administration.

9.4 Material

9.4.1 Where materials other than steel are used, the scantlings are to be specially considered.

9.5 Scantlings of subdivision structure other than doors

9.5.1 The minimum scantlings of subdivision bulkheads and casings are to be derived in accordance with Table 1.9.1 Watertight and deep tank bulkhead scantlings for watertight bulkheads, where h ₄ is to be substituted by either of h _T, h _L or h _c, depending on the location under consideration.

9.5.2 Where a cut-out is made in the subdivision structure for the fitting of an access door, the strength and integrity of the subdivision structure are to be maintained.

9.6 Scantlings of subdivision doors

9.6.1 The plate thickness of subdivision doors of single plate construction is not to be less than the greater of:

0,004s f(h k)^0,5 mm, or

5,0 mm

where

s, k	=	as defined in Pt 4, Ch 2, 1.5 Symbols 1.5.1
f	=	as defined in Table 1.9.1 Watertight and deep tank bulkhead scantlings in Pt 4, Ch 1 General Cargo Ships
h	=	h _T, h _L or h _c as defined in Pt 4, Ch 2, 9.2 Design loads 9.2.3, as appropriate.

9.6.2 For subdivision doors of a double plate construction the plate thickness is to be specially considered.

9.6.3 The scantlings of primary and secondary stiffeners of subdivision doors are to be based on direct strength calculations.

9.6.4 The direct strength calculations are also to provide an assessment of the door, under the design load, to enable the leakage and hence the drainage requirements of Pt 4, Ch 2, 9.9 Watertightness and drainage to be assessed.

9.6.5 For the purpose of the direct strength calculations. the stresses induced in the subdivision door, determined using the design loads from Pt 4, Ch 2, 9.2 Design loads, are not to exceed the permissible values given in Table 2.9.1 Permissible stress values. Checks are also to be carried out to ensure that the door will not buckle under the design loads.

Table 2.9.1 Permissible stress values

Stress type	Permissible stress
Direct stress	σ_o
Shear stress
Combined stress	σ_o
Symbols
σ_o = specified minimum yield stress, in N/mm²

9.6.6 Where a cut-out is made within the subdivision door for the fitting of an access door, the strength of the subdivision door is to be maintained.

9.7 Closing, securing and supporting of subdivision doors

9.7.1 The closing and securing devices of doors are to comply with the following requirements:

Securing devices are to be simple to operate and easily accessible. They are to be of a design approved by LR for the intended purpose.
Securing devices and supporting devices are to be designed to withstand the design loads calculated in Pt 4, Ch 2, 9.2 Design loads 9.2.1 in association with the permissible stresses shown in Table 2.9.2 Permissible stress values.
The arrangement of securing and supporting devices is to be such that threaded bolts do not carry support forces. The maximum tensile stress in way of threads of bolts not carrying support forces is not to exceed 0,5σ_o.
For steel to steel bearings in securing and supporting devices, the bearing pressure is not to exceed 0,8σ_o. For other bearing materials, the permissible bearing pressure is to be determined according to the manufacturer’s specification. The bearing pressure is to be calculated by dividing the design force by the projected bearing area.
Only the active supporting and securing devices having an effective stiffness in the relevant direction are to be included when calculating the reaction forces acting on the devices.
Securing devices are to be equipped with positive locking arrangements. Arrangements are to be such that the securing devices are retained in the closed position within design limits of inclination, vibration and other motion-induced loads and in the event of loss of any actuating power supply.
Hydraulic systems are to comply with Pt 5, Ch 14, 9 Hydraulic systems.
Control and monitoring arrangements are to comply with Pt 6, Ch 2, 19 Ship safety systems.

Table 2.9.2 Permissible stress values

Stress type	Permissible stress
Direct stress	0,8σ_o
Shear stress	0,5σ_o
Combined stress	0,8σ_o
Symbols
σ_o = specified minimum yield stress, in N/mm²

9.7.2 The reaction forces to be applied to the effective securing and supporting devices are to be determined using the applicable design loads calculated using the heads in Pt 4, Ch 2, 9.2 Design loads together with the weight of the door.

9.8 Access doors

9.8.1 Access doors are permitted to be fitted in subdivision doors or bulkheads in order to provide acess between compartments.

9.8.2 Access doors may be manually operated.

9.8.3 The strength of access doors is to be not less than that of the surrounding structure.

9.8.4 Means are to be provided to ensure that access doors are closed and secured when not in use after the ship has left the berth.

9.8.5 A notice is to be displayed on the access doors stating that the door is to be closed and secured at all times when not in use, when the ship is under way.

9.8.6 Means are to be provided on the navigation bridge to indicate whether the access doors are opened or closed.

9.9 Watertightness and drainage

9.9.1 Subdivision doors and access doors are to be fitted with gaskets in order to minimise leakage. For access doors where down flooding could result, particular attention is to be paid to drainage requirements.

9.9.2 The gasket arrangement shall provide sufficient flexibility to absorb possible racking deformation.

9.9.3 Attention is drawn to the drainage requirements of Pt 5, Ch 13, 3.1 General with respect to the compartments created by subdivision structures.

9.9.4 The drainage arrangement for each compartment is to have sufficient capacity to handle leakage from any adjacent flooded compartment.

9.10 Ventilation of vehicle deck spaces

9.10.1 Attention is drawn to the ventilation requirement of Pt 6, Ch 2, 14.13 Special requirements for ships with spaces for carrying vehicles with fuel in their tanks, for their own propulsion 14.13.3, since subdivision structure could disrupt air flow.

9.11 Operating and Maintenance Manual

9.11.1 An Operating and Maintenance Manual for the subdivision doors is to be provided on board and is to contain the following:

main particulars and design drawings,
service conditions (e.g. service area restrictions),
maintenance and function testing,
register of inspections, repairs and renewals.

9.11.2 The Manual is to be submitted for approval. It is to contain a note recommending that recorded inspections of supporting and securing devices are to be carried out by the ship's staff at monthly intervals, or following incidents that could result in damage, including heavy weather or contact in the region of the subdivision doors. Any damages recorded during such inspections are to be reported to LR.

9.11.3 Documented operating procedures for closing and securing the subdivision doors are to be kept on board and posted in an appropriate place.