Section 1 General
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Ships, July 2022 - Part 4 Ship Structures (Ship Types) - Chapter 4 Offshore Support Vessels - Section 1 General

Section 1 General

Parent topic: Chapter 4 Offshore Support Vessels

1.1 Application

1.1.1 This Chapter applies to sea-going ships specially designed and constructed to support the operations of offshore installations, including the carriage of specialised stores and cargoes to such facilities. These may be defined as:

  1. AHTS: Assigned to vessels designed for anchor handling, towing and supply of specialised stores and cargo.
  2. Anchor handler: Assigned to vessels specially designed, constructed and equipped for handling anchors used to secure floating offshore installations.
  3. Cable laying vessel: Assigned where special consideration has been given to operations for laying/maintaining underwater cables.
  4. Diving support vessel: Assigned where a diving system has been installed and where special consideration has been given to the launch and recovery systems for diving operations, including the strength and continuity in way of moon pools, large hatches, heavy loads, etc.
  5. Offshore supply vessel: Assigned to vessels designed for the carriage of specialised stores and cargoes to fixed or floating offshore installations.
  6. Offshore support vessel: Assigned to vessels designed for the provision of support services to fixed or floating offshore installations.
  7. Offshore well stimulation ship: Assigned where a plant has been installed and where special consideration has been given to operations associated with the stimulation of wells for offshore oil/gas production.
  8. Pipe laying vessel: Assigned where special consideration has been given to operations for laying/maintaining pipes associated with offshore oil/gas production.
  9. Seismographic support vessel: Assigned where special consideration has been given to operations associated with seismographic research and survey.
  10. Standby vessel: Assigned to vessels designed to provide rescue assistance and afford safe refuge in the event of an emergency on or near an offshore installation.
  11. Subsea support vessel: Assigned where special consideration has been given to operations associated with subsea construction and installation support, inspection, repair and maintenance.

1.1.2 Where appropriate, LR may request direct calculations or additional requirements to be complied with, for novel or additional features pertinent to a given Ship Type listed within this Chapter, see also Pt 3, Ch 1, 2.1 General 2.1.1.

1.1.3 The scantlings and arrangements are to be as required by Pt 4, Ch 1 General Cargo Ships, except as otherwise specified in this Chapter.

1.1.4 Attention is drawn to the need for Masters to be able to assess the stability of their ships quickly and accurately in all service conditions, see Pt 1, Ch 2, 3 Surveys - General.

1.1.5 Where towing equipment is fitted, the requirements of Pt 4, Ch 3, 7 Towing arrangements are to be applied.

1.1.6 Attention is drawn to the National and International standards applicable to vessels in this chapter as required by the Flag Administation

1.2 Class notations

1.2.1 In general, ships complying with the requirements of this Chapter and relevant additional requirements will be eligible for one or a combination of the notations indicated in Table 4.1.1 Type notations applicable to offshore support vessels.

Table 4.1.1 Type notations applicable to offshore support vessels

Class Notation Requirements
Offshore support vessel Pt 4, Ch 4, 1 General to Pt 4, Ch 4, 8 Transport and handling of hazardous and noxious liquid substances in bulk
Offshore supply vessel Pt 4, Ch 4, 1 General to Pt 4, Ch 4, 8 Transport and handling of hazardous and noxious liquid substances in bulk
Cable laying vessel  
Pipe laying vessel  
Diving support vessel Pt 4, Ch 4, 1 General, Pt 4, Ch 4, 2 Longitudinal strength, Pt 4, Ch 4, 7 Engine exhaust outlets and Pt 4, Ch 4, 8 Transport and handling of hazardous and noxious liquid substances in bulk, see Note 2
Subsea support vessel  
Seismographic support vessel  
Standby vessel Pt 4, Ch 4, 1 General to Pt 4, Ch 4, 8 Transport and handling of hazardous and noxious liquid substances in bulk
Anchor handler Pt 4, Ch 4, 1 General to Pt 4, Ch 4, 8 Transport and handling of hazardous and noxious liquid substances in bulk
Offshore Tug Pt 4, Ch 3, 1 General to Pt 4, Ch 3, 8 Fenders and Pt 4, Ch 4, 1 General to Pt 4, Ch 4, 8 Transport and handling of hazardous and noxious liquid substances in bulk
AHTS (Anchor Handler Tug Supply) Pt 4, Ch 3, 1 General to Pt 4, Ch 3, 8 Fenders; and
Pt 4, Ch 4, 1 General to Pt 4, Ch 4, 8 Transport and handling of hazardous and noxious liquid substances in bulk

Note 1. A ship designed to fulfil more than one function can be assigned a combination of the notations listed above, e.g.:

  • 100A1 Offshore supply vessel/Standby vessel
  • 100A1 Offshore supply vessel /Anchor handler
  • 100A1 Offshore supply vessel /Standby vessel/Oil Recovery
  • Any combination of the requirements listed in this Table.

Note 2. LR may request direct calculations or additional requirements to be complied with, see Pt 4, Ch 4, 1.1 Application 1.1.2
1.2.2 The following additional special features may be requested:
  • EWP (Enhanced Weather Protection):

    The notation EWP may be added if the vessel complies with requirements in Pt 4, Ch 4, 9 Enhanced weather protection, e.g. Offshore supply vessel EWP. The notation is mandatory for vessels that are intended for unrestricted worldwide service and that are required to stay on station in adverse weather conditions. The enhanced features provide additional protection in harsh weather.

  • Oil Recovery:

    A vessel complying with the requirements of Pt 7, Ch 5 Ships Equipped for Oil Recovery Operations will be eligible for the notation Oil Recovery.

  • WDL(+) (Weather deck load):

    If the weather deck scantlings have been approved for a loading greater than a design head of 3,5 m, the notation WDL(+) may be added. If requested, the maximum permissible weather deck load and extent can be identified in the notation, e.g. WDL(5,0 t/m2 from Aft to Fr. 26).

  • RD (Relative density):

    Where a ship has tanks appraised for a maximum permissible relative density greater than 1,025, the notation RD(specified tank names, density) may be added, see Pt 4, Ch 1 General Cargo Ships.

  • LFPL (Low flashpoint liquids):

    Ships intended for the carriage of liquids with flash point below 60°C (closed-cup test) in bulk are to be built and equipped in accordance with the relevant requirements of Pt 4, Ch 4, 8 Transport and handling of hazardous and noxious liquid substances in bulk and will be given the class notation LFPL. If requested, the concerned cargo, flash point (closed-cup test) and tank can be identified in the notation, e.g. LFPL(methanol, 12°C, No. 7 centre tank).

1.2.3 The Regulations for classification and the assignment of class notations are given in Pt 1, Ch 2 Classification Regulations, to which reference should be made.

1.3 Information required

1.3.1 In addition to the information and plans required by Pt 3, Ch 1, 5 Information required, plans covering the following items are to be submitted where applicable:

  • Independent cargo tanks.
  • Cargo tank foundations and securing arrangements.
  • Towing arrangements, including supports and foundations of towing winches.
  • Arrangements for the stowage of deck cargoes (cargo containment) and details of any associated racks or other similar structures and their supports/foundations together with information to indicate design loads.
  • Movable decks, including the stowing arrangements for portable components.
  • Freeing arrangements.

1.3.2 In addition to the information and plans required by Pt 4, Ch 4, 1.3 Information required 1.3.1, details of local strengthening for the following items are to be submitted where applicable:

  • The arrangement and integration into the hull of equipment, tanks, supports, foundations, etc. in conjunction with their mass, working load and holding capability information.
  • For unusual structural arrangement and equipment, calculations are to be submitted showing acceptable structural strength.
  • Supports and foundations for anchor handling and laying arrangements for anchors carried as cargo.
  • Supports for towing arrangements.
  • The arrangement for fast rescue craft.

1.4 Symbols

1.4.1 The symbols are as defined in Pt 4, Ch 1, 1.5 Symbols and definitions.

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