Glossary
Browse the IADC Lexicon alphabetically or by category. Get comprehensive definitions of drilling industry terms.
Draught T0
Definition(s)
Draught T0
Draught, T0, is the maximum design operating summer draught, in metres, measured from top of keel. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 4, Steel Unit Structures, June 2013, Lloyd’s Register, Global StandardsDepth D
Definition(s)
Depth D
Depth, D, is measured, in metres, at the middle of the length, L, from the top of keel to top of the deck beam at side on the uppermost continuous deck. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 4, Steel Unit Structures, June 2013, Lloyd’s Register, Global StandardsRule Length
Definition(s)
Rule Length
Rule length, L, in metres, for self-elevating units and semi-submersible units with twin lower hulls is to be taken as 97 per cent of the extreme length on the maximum design transit waterline measured on the centreline or on a projection of the centreline, see Fig. 1.5.1.
Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 4, Steel Unit Structures, June 2013, Lloyd’s Register, Global Standards
Rule Length
The Rule length, L, for surface type units is the distance, in metres, on the summer load waterline from the forward side of the stem to the after side of the rudder post or to the centre of the rudder stock if there is no rudder post. L is to be not less than 96 per cent, and need not be greater than 97 per cent, of the extreme length on the summer load waterline. In ships with unusual stem or stern arrangements the Rule length, L, will be specially considered. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 4, Steel Unit Structures, June 2013, Lloyd’s Register, Global StandardsTaut-leg Mooring
Definition(s)
Taut-leg Mooring
A system that relies principally for its compliance on the axial extensibility of the mooring line rather than the catenary profile. Such moorings provide a significant upward load on the seabed connection. Source: API RP 2SM Design, Manufacture, Installation, and Maintenance of Synthetic Fiber Ropes for Offshore Mooring, Second Edition, July 2014. Global Standards Source: API RP 2SM, Design, Manufacture, Installation, and Maintenance of Synthetic Fiber Ropes for Offshore Mooring, First Edition, July 2014. Global StandardsTaut-leg Mooring
A mooring system based on light-weight anchor lines pre-tensioned to a taut configuration with no significant catenary shape at any unit offset, and applying vertical and horizontal loads at the anchor points. With this type of system, compliancy is derived from the inherent axial elastic stretch properties of the anchor line. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsThruster-assist
Definition(s)
Thruster-assist
The use of thrusters, inclusive of their associated equipment, to supplement the unit’s positional mooring system. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsSurface Type Jack-up Unit
Definition(s)
Surface Type Jack-up Unit
A surface type self-elevating (or jack-up) unit is a floating unit, which is designed to operate as a sea bed stabilized unit in an elevated mode. These units have a ship type displacement hull of single or multiple hull construction fitted with moveable legs capable of raising the hull above the surface of the sea. The legs may be designed to penetrate the sea bed, or be attached to a mat or individual footings which rest on the sea bed. In general, installation and maintenance activities would be undertaken in the jacked-up condition. These unit types are generally self-propelled. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsSurface Type Self-elevating (or jack-up) Unit
Definition(s)
Surface Type Self-elevating (or jack-up) Unit
A surface type self-elevating (or jack-up) unit is a floating unit, which is designed to operate as a sea bed stabilized unit in an elevated mode. These units have a ship type displacement hull of single or multiple hull construction fitted with moveable legs capable of raising the hull above the surface of the sea. The legs may be designed to penetrate the sea bed, or be attached to a mat or individual footings which rest on the sea bed. In general, installation and maintenance activities would be undertaken in the jacked-up condition. These unit types are generally self-propelled. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsSurface Type Floating Unit
Definition(s)
Surface Type Floating Unit
A surface type floating unit is a unit with a ship or barge type displacement hull of single or multiple hull construction intended for operation in the floating condition. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsSelf-elevating or (Jack-up) Unit
Definition(s)
Self-elevating or (Jack-up) Unit
A self-elevating (or jack-up) unit is a floating unit which is designed to operate as a sea bed-stabilised unit in an elevated mode. These units have a buoyant hull (generally either triangular or pontoon shaped) with movable legs capable of raising its hull above the surface of the sea. The legs may be designed to penetrate the sea bed, or be attached to a mat or individual footings which rest on the sea bed. These unit types are generally not fitted with a propulsion system. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsRiser Components
Definition(s)
Riser Components
Valves, connections, etc., andsimilar apparatus incorporated in the riser system. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsRiser Support
Definition(s)
Riser Support
Any structural item used for connecting a part of the riser system to the unit. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsLiftboat
Definition(s)
Liftboat
A liftboat is a unit with a buoyant hull (generally either triangular or pontoon shaped) with moveable legs capable of raising the hull above the surface of the sea and designed to operate as a sea bed-stabilised unit in an elevated mode. The legs may be designed to penetrate the sea bed, or be attached to a mat or individual footings which rest on the sea bed. In general, installation and maintenance activities would be undertaken in the jacked-up condition. These unit types are generally self-propelled. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsJack-up Unit
Definition(s)
Jack-up Unit
A self-elevating (or jack-up) unit is a floating unit which is designed to operate as a sea bed-stabilised unit in an elevated mode. These units have a buoyant hull (generally either triangular or pontoon shaped) with movable legs capable of raising its hull above the surface of the sea. The legs may be designed to penetrate the sea bed, or be attached to a mat or individual footings which rest on the sea bed. These unit types are generally not fitted with a propulsion system. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsFloating Pipe
Definition(s)
Floating Pipe
A surface pipe between the singlepoint mooring or buoy and the ship manifold. The floating pipe is normally permanently attached to the single-point mooring. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global StandardsType Notation
Definition(s)
Type Notation
A notation indicating that the unit has been arranged and constructed in compliance with the particular Rules intended to apply to that type of unit, e.g., Mobile drilling unit. Typical type notations are defined in Part 3. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 1, Regulations, June 2013, Lloyd’s Register, Global StandardsSpecial Features Notation
Definition(s)
Special Features Notation
A notation indicating that the unit incorporates special features which significantly affect the design, e.g., DRILL. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 1, Regulations, June 2013, Lloyd’s Register, Global StandardsSupport Vessel
Definition(s)
Support Vessel
Alternative name for a support unit as defined in 2.1.13. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 1, Regulations, June 2013, Lloyd’s Register, Global StandardsSpecial Duties Notation
Definition(s)
Special Duties Notation
A notation indicating that the unit has been designed, modified or arranged for special duties other than those implied by the type notation, e.g., oil exploration. Units with special duties notations are not thereby prevented from performing any other duties for which they may be suitable. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 1, Regulations, June 2013, Lloyd’s Register, Global StandardsSheltered Water
Definition(s)
Sheltered Water
Water where the fetch is six nautical miles or less. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 1, Regulations, June 2013, Lloyd’s Register, Global StandardsReasonable Weather
Definition(s)
Reasonable Weather
Wind strengths of force six or less in the Beaufort scale, associated with sea states sufficiently moderate to ensure that green water is taken on board the unit’s weather deck at infrequent intervals only, or not at all. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 1, Regulations, June 2013, Lloyd’s Register, Global StandardsPositional Mooring
Definition(s)
Positional Mooring
Anchoring system for position keeping at the unit's working location prompt and thorough repair a permanent repair completed at the time of survey to the satisfaction of the surveyor, therein removing the need for the imposition of any associated condition of class. Source: Rules for Classification – Offshore units, DNVGL-OU-0101, Offshore drilling and support units, DNV GL, July 2015. Global StandardsPositional Mooring
Station-keeping by means of multi-leg mooring systems with or without thruster assistance. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 1, Regulations, June 2013, Lloyd’s Register, Global StandardsPositional Mooring
Station-keeping by means of multi-leg mooring system with or without thruster-assist. The positional mooring system will consist of the following components, as relevant:- Anchor points:
• Drag embedment anchors.
• Anchor piles.
• Suction anchor piles.
• Gravity anchors.
• Plate anchors.
2. Anchor lines. 3. Anchor line fittings:• Shackles.
• Connecting links/plates.
• Wire rope terminations.
• Clump weights.
• Quick release devices, etc.
4. Fairleads/bending shoes. 5. Chain or wire rope stoppers. 6. Winches or windlasses. Where applicable, the structural or mechanical connection of these items to the unit is also considered to be part of the positional mooring system. Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global Standards