Section 1 General

1.1.1 The requirements of this Chapter apply to Clasifications Register (hereinafter referred to as 'LR') classed ships with positional mooring systems or thruster-assisted positional mooring systems and are additional to those applicable in other Parts of the Rules. The Rules are not intended to apply to vessels which have station-keeping capabilities, but which are not required to remain on station in adverse weather conditions. This normally precludes the Rules being applicable to small ships.

1.1.2 Compliance with this Chapter is not mandatory, but ships provided with a positional mooring system or thruster-assisted positional mooring system which do comply will be eligible for an appropriate class notation which will be recorded in the Register Book at the specific request of an Owner.

1.1.3 The mooring system will be considered for classification with LR on the basis of operating constraints and procedures specified by the Owner and recorded in the Operations Manual.

1.1.4 Requirements, additional to these Rules may be imposed by the National Authority with whom the ship is registered and/or by the administration within whose territorial jurisdiction it is intended to operate.

1.2.1 Ships provided with a positional mooring system which complies with the requirements of this Chapter will be eligible to have included in the class notation one of the following special features notations:

1. For ships fitted with a positional mooring system:

   PM (Positional mooring system); or

   PMC (Positional mooring system for mooring in close proximity to other ships or installations. This notation will apply in particular to any ship operating in conjunction with a fixed installation, e.g. crane barge, accommodation unit, maintenance vessel, etc.)

2. For ships fitted with a thruster-assisted positional mooring system:

   PM [T1circ] [or [T2circ] or [T3circ] ]

   or

   PMC [T1circ] [or [T2circ] or [T3circ] ]

   The numeral in the circled supplementary notation, [T1circ], etc. defines the thruster allowance which may be permitted in the design of the positional mooring system, and is determined by the capacity/redundancy of the thrust/machinery installation, see Table 8.3.2 Thruster allowance.

1.2.2 Additional descriptive notes may be given and entered in column 6 of the Register Book indicating the type of positional mooring system, reference system, control system, limiting environmental criteria, etc.

1.2.3 Ships provided with a nearshore positional mooring system which complies with the requirements of Pt 3, Ch 10, 16 Long-term nearshore positional mooring system of the Rules and Regulations for the Classification of Offshore Units, July 2022 will be eligible for the assignment of special features class notation LTMOOR (Long-term Terminal Mooring). This notation applies to a nearshore ‘dry mooring system’ to jetty or quay but not a ‘wet mooring system’ anchored to the sea bed. Strength and fatigue assessments are to be carried out in accordance with the ShipRight procedure for Long-Term Nearshore Positional Mooring Systems.

1.3.1 The positional mooring and thruster-assisted positional mooring systems and their associated equipment are to be examined and tested during construction and under working conditions on completion of the installation. The Periodical Survey of these items is to be arranged to coincide with Hull and Machinery Surveys as required by other Parts of these Rules.

1.4.1 Positional mooring is a method of station keeping by means of multiple anchor lines laid out in catenary array. Each positional mooring system is to consist of the following:

1. Anchors or anchor piles.

2. Anchor lines.

3. Anchor line fittings (shackles, connecting links, wire rope terminations, quick release devices, etc.).

4. Fairleads.

5. Winches or windlasses.

6. Chain or wire rope stoppers.

Where applicable, the structural or mechanical connection of these items to the ship is also considered to be part of the positional mooring system.

1.4.2 `Thruster-assisted Mooring' is the use of thrusters and main propulsion, if so designed, to supplement the ship's anchoring system.

1.5.1 The information and plans specified in Pt 7, Ch 8, 1.5 Plans and data submission 1.5.2to Pt 7, Ch 8, 1.5 Plans and data submission 1.5.5 are to be submitted in triplicate. One copy of the Operations Manual referred to in Pt 7, Ch 8, 1.5 Plans and data submission 1.5.6 is to be forwarded for information.

1.5.2 Plans and data dealing with positional mooring arrangements and the associated equipment are to be submitted, including the following:

1. Mooring arrangements with details of mooring patterns, anchor lines and fittings, etc.

2. Mooring equipment with details of anchors, fairleads and cable stoppers.

3. Winches or windlasses with details of gearing shafting, brake systems, ratchet and pawl, drum/cable lifter and frame.

1.5.3 For thruster-assisted positional mooring systems, plans of the following, together with particulars of ratings, in accordance with the relevant Parts of these Rules are to be submitted for the following:

1. Prime movers, gearing, shafting, propellers and thrust units, see also Pt 5, Ch 8 Shaft Vibration and Alignment.

2. Machinery piping systems.

3. Electrical installations.

In addition, details of proposals for the redundancy provided in machinery, electrical installations and control systems are to be submitted. These proposals are to take account of the possible loss of performance capability should a component fail. Where a common power source is utilised for thrusters, details of the total maximum load required for thruster-assist are to be submitted.

1.5.4 Plans of control, alarm and safety systems, including the following, are to be submitted:

1. Functional block diagrams of the control system(s).

2. Functional block diagrams of the position reference systems and the environmental sensors.

3. Details of the electrical supply to the control system(s), the position reference system(s) and the environmental sensors.

4. Details of the monitoring functions of the controllers, sensors and reference system, together with a description of the monitoring functions.

5. List of equipment with identification of the manufacturer, type and model.

6. Details of the overall alarm system linking the centralised control station, subsidiary control stations, relevant machinery spaces and operating areas.

7. Details of the control stations, e.g. control panels and consoles, including the location of the control stations.

8. Test schedules which are to include the methods of testing and the test facilities provided.

1.5.5 The following supporting plans, data, calculations or documents are to be submitted:

1. General arrangement showing plan views, side elevations and sections of the ship.

2. Design criteria showing operating and survival environment, water depth range and required station keeping limits.

3. Environmental forces on ship showing wind, current and wave drift. These forces are to be verified by direct calculation, model test reports, or full-scale data, etc.

4. Ship motions showing first order wave motions, surge, sway and yaw. Tank test data or equivalent to be provided.

5. Mooring analysis, including computer printout where relevant.

6. Strength calculations for anchors, fairleads, winches/ windlasses, cable stoppers and special fittings.

7. Thruster arrangements for thruster-assist systems, including powers, thrusts and interactions between thrusters, thruster and hull, thruster and current.

1.5.6 An Operations Manual for the system is to be placed on board the ship. This Manual is to contain all necessary information and instructions regarding positional mooring and, where relevant, thruster-assisted positional mooring. It would normally also contain descriptions of the following:

• Mooring systems.
• Laying the mooring system.
• Anchor pre-loading.
• Pre-tensioning anchor lines.
• Tension adjustment.
• Winch performance.
• Winch operation.
• Procedure in event of failure or emergency.
• Procedure for operating thrusters.
• Fault-finding procedures for thruster-assist system.