Section 4 Submersible handling systems

4.1.1 This Section applies to installations which are designed to launch and recover manned and unmanned submersibles in an open sea environment from ships or semisubmersible vessels. For the purpose of these requirements, the term ‘manned submersible handling systems’ includes the handling of manned diving systems. Generally, the significant wave height will not exceed 2,0 m for manned submersible handling operations, but may be higher for unmanned operations. Special consideration will be given to cases where service in a significant wave height above 2,0 m is envisaged for manned submersible operations.

4.1.2 The design requirements of Ch 4, 3 Offshore cranes are to apply to all submersible handling systems except where specific requirements are defined in this Section.

4.1.3 The general requirements for machinery items are provided in Ch 9 Machinery. Specific requirements for machinery items engaged in manned submersible handling operations are provided in Ch 9, 4 Machinery engaged in handling of personnel and Ch 9, 5 Hydraulic cylinders (as applicable). In addition to approving the structural arrangements for manned submersible handling systems, details of the machinery items (e.g. winches (main and secondary), including all torque transmitting components) are to be submitted for approval.

4.1.4 An alternative (secondary) means of recovery is to be provided for all manned submersible handling systems that are dependent on the handling system for regaining the surface. In addition to the main and alternative means of retrieval, an emergency means of retrieval is defined in Pt 5, Ch 7 Lifting Appliances of the Rules and Regulations for the Construction & Classification of Submersibles & Diving Systems.

4.2.1 A duty factor, F_d, of 1,2 is to be used for all submersible handling systems, while the submersible is suspended over the side of the ship or in the moonpool. A reduced duty factor may be considered once the submersible is safely inboard the ship (see Table 4.4.1 Dynamic factors and design parameters for submersible handling systems). Alternative proposals to use lower duty factors shall be based on the principles outlined in Ch 4, 2.3 Duty factor 2.3.2 to Ch 4, 2.3 Duty factor 2.3.4 and will be specially considered.

4.3.1 The live load, L _l, to be used for submersible handling systems is to be taken as the greater of:

1. The maximum in-air weight of the submersible, the in-air weight of items (e.g. the hook) which are connected to the submersible and the exposed length of hoisting rope extending from the winch to the hook.

2. The maximum weight of the exposed length of hoisting rope extending from the winch to the air/water interface, together with the combined in-water weight of the submersible, the in-water weight of items (e.g. the hook) which are connected to the submersible and the submerged length of hoisting rope extending from the air/water interface to the hook.

The weight of entrained or trapped water needs to be considered for the evaluation of the weight of the submersible.

4.3.2 Where the handling system does not lift the submersible through the air/water interface, the live load may be taken as that defined in Ch 4, 4.3 Basic loads 4.3.1.(b).

4.4.1 The hoisting factor, F_h,swh, to be used for submersible handling systems incorporates the effects of the submersible passing through the air/water interface as well as accelerations from ship motions acting on the live load.

4.4.2 Where possible, the hoisting factor is to be based on actual accelerations or from model predictions for the mother ship’s behaviour, taking into account the ship’s headings and the sea conditions.

4.4.3 Where actual accelerations or model predictions are not available, the minimum default values of the hoisting factor, F_h,swh, for different sea conditions (e.g. significant wave heights) and with the submersible in various positions in the operating cycle are given in Table 4.4.1 Dynamic factors and design parameters for submersible handling systems. Values of F_h,swh for intermediate significant wave heights can be obtained by interpolation.

4.4.4 Where the design parameters given in Table 4.4.1 Dynamic factors and design parameters for submersible handling systems are used, further calculations and/or further (operational) assessment should be carried out, in order to ensure that the design parameters taken from that Table are not exceeded during the actual operation of the submersible handling system, taking into account influences such as vessel accelerations, wind, hoisting factor, heel/trim angle, offlead/sidelead angle, effects of the air/water interface (splash zone), effects of added mass, drag and current forces, seabed suction, etc.

4.4.5 The horizontal components of force derived from the angles of heel, trim, offlead and sidelead are to be multiplied by the hoisting factor appropriate for the phase in the launch and recovery cycle (see Table 4.4.1 Dynamic factors and design parameters for submersible handling systems).

4.5.1 The design wind speed for operational conditions shall be taken as at least 20 m/s, corresponding to a wind pressure exceeding 250 N/m². Reference is made to the specified service category as defined in Ch 1, 2.3 Service category 2.3.2.

4.5.2 The stowage wind speed is to be taken as at least 63 m/s.

4.5.3 Proposals for the application of the wind speeds will be specially considered.

4.5.4 all wind speeds are to be related to gust wind speeds averaged over a duration of 3 seconds.

4.6.1 Submersible handling systems operate in an open sea environment where there is significant movement of the ship and/or submersible due to wave action. To allow for these conditions, simultaneously acting offlead and sidelead angles are to be used for design purposes, while the submersible is in the water, passing through the air/water interface, or is in the splash zone. Minimum default values for the offlead and sidelead angles to be used for different sea conditions are given in Table 4.4.1 Dynamic factors and design parameters for submersible handling systems.

4.6.2 Where the design parameters given in Table 4.4.1 Dynamic factors and design parameters for submersible handling systems are used, further calculations and/or further (operational) assessment should be carried out, in order to ensure that the offlead and sidelead angles as defined in that Table are not exceeded during the actual operation of the submersible handling system.

4.7.1 When the submersible is out of the splash zone and in air, the offlead and sidelead angles will not be acting. However, horizontal loads from the effects of the roll and pitch of the mother ship will still need to be considered to be acting on the submersible and self-weight of the handling system. These may be expressed as static angles of heel and trim and minimum default values for different sea states are given in Table 4.4.1 Dynamic factors and design parameters for submersible handling systems.

4.7.2 Where the design parameters given in Table 4.4.1 Dynamic factors and design parameters for submersible handling systems are used, further calculations and/or further (operational) assessment should be carried out, in order to ensure that the heel and trim angles as defined in that Table are not exceeded during the actual operation of the submersible handling system. The calculations and/or assessment should further take into account the loads due to vessel motions (e.g. heel and trim, roll and pitch, vessel accelerations).

4.8.1 In addition to the operating conditions, the installation is to be designed to withstand the most severe combination of motions which can occur when the handling system is stowed. In the case of ship mounted installations, see Ch 4, 2.11 Forces due to ship motion.

4.8.2 The loads originating from the submersible being stowed in the submersible handling system need to be considered.

4.8.3 The effects of ‘green sea loading’ on the structure will be subject to special consideration.

4.9.1 Materials for submersible handling systems are to comply with the requirements of Ch 4, 2.25 Materials, Ch 4, 3.8 Materials and Ch 11 Materials and Fabrication.

4.9.2 If slewing rings are applied in the design of the submersible handling system, they are to comply with Ch 4, 3.7 Slew rings.

4.10.1 The minimum safety factors, SF_swh,steel and SF_{swh,synthetic}, for ropes used for manned submersibles is to be taken as 8,0 for steel wire ropes and 10,0 for synthetic fibre ropes. Where manned submersible operations take place in conditions in which the significant wave height exceeds 2,0 m, where the hoisting factor, F_h,swh, is greater than 1,7, the rope safety factor is to be increased as follows:

SF_swh,steel = 8,0 for steel wire ropes, or

SF_{swh,synthetic} = 10,0 for synthetic fibre ropes

For submersible handling systems with .

and

The factor is not to be taken as less than 1,0.

4.10.3 The minimum safety factor, SF _{swh,synthetic}, for synthetic fibre ropes used for unmanned submersibles is to be obtained from Ch 4, 4.10 Rope safety factors 4.10.2, multiplied by 1,25.

4.10.4 If in addition to the primary hoisting rope, an alternative (secondary) system of recovery is employed using another hoisting rope, the minimum safety factor for this rope is to be not less than for steel wire rope and for synthetic fibre rope. The factor is not to be taken as less than 1,0.

4.11.1 Cradles and their rails that are used to transfer diving bells or manned submersibles from the deck to the Transfer Under Pressure (TUP) facilities are to be designed in accordance with Ch 4, 2 Shipboard cranes, taking due account of the accelerations from ship motions, in both the operational and survival conditions.

4.12.1 The load testing requirements for manned submersible handling systems are given in Ch 12, 1.7 Manned submersible handling systems.

4.12.2 The load testing requirements for unmanned submersible handling systems are given in Ch 12, 1.6 Cranes and ROV handling systems.