Section 2 General requirements

2.1.1 In general, for a ship to be assigned an unrestricted service notation, a minimum of two podded propulsion units is to be provided where these form the sole means of propulsion. For vessels where a single podded propulsion unit is the sole means of propulsion, an evaluation of a detailed engineering justification will be conducted by LR, see Vol 2, Pt 4, Ch 4, 2.2 Documentation required for design review 2.2.2. This evaluation process will include the appraisal of a Risk Assessment (RA) to verify that sufficient levels of redundancy and monitoring are incorporated in the podded propulsion unit’s support systems and operating equipment.

2.2.1 In addition to the plans required by Vol 2, Pt 3, Ch 1 Gearing and Vol 2, Pt 3, Ch 2 Shafting Systems, Vol 2, Pt 4, Ch 1 Propellers, Vol 2, Pt 5 Shaft Vibration and Alignment, Vol 2, Pt 6, Ch 1 Steering Gear, Vol 2, Pt 7, Ch 3 Machinery Piping Systemsand Vol 2, Pt 9 Electrotechnical Systems and Vol 2, Pt 10 Human Factors, the following plans and information are required to be submitted for appraisal. Where appropriate, the information shall be contained in a System Design Description document, see Vol 2, Pt 1, Ch 3, 3.5 System design description:

1. Description of the ship’s purpose/capabilities together with the pod’s intended operational modes in support of these capabilities. The operational modes are to include stopping the vessel and restrictions on steering angles at different ship speeds. See also Vol 2, Pt 4, Ch 4, 2.2 Documentation required for design review 2.2.1.(h).

2. The declared steering angle limits are to be stated by the steering system manufacturer for each podded propulsion unit;

3. Power transmitted at MCR condition (shaft power and rpm) and other maximum torque conditions, e.g. bollard pull.

4. Maximum transient thrust, torque and other forces and moments experienced during all envisaged operating modes as permitted by the steering and propulsor drive control systems.

5. Details of the electric propulsion motor short-circuit torque and motor air gap tolerance.

6. Sectional assembly in the Z-X plane, see Figure 4.2.1 Pod co-ordinate system.

7. Specifications of materials and NDE procedures for components essential for propulsion and steering operation, to include propulsion shaft and slewing ring bearings, gearing and couplings, see Vol 2, Pt 4, Ch 4, 3.1 General.

8. Details of the intended manoeuvring capability of the ship in each operating condition.

9. Design loads for both the pod structure and propeller together with podded propulsion unit design operating modes,see Vol 2, Pt 4, Ch 4, 2.4 Global loads 2.4.1, Vol 2, Pt 4, Ch 4, 5.3 Propulsion shafting 5.3.7, Vol 2, Pt 4, Ch 4, 5.6 Steering system 5.6.10 and Vol 2, Pt 4, Ch 4, 5.6 Steering system 5.6.11.

10. Supporting data and direct calculation reports. This is to include, where applicable an assessment of anticipated global accelerations acting on the ship's machinery and equipment which may potentially affect the reliable operation of the propulsion system for all foreseeable seagoing and operating conditions. Typically, this may include response to slamming, extreme ship motions and pod interaction. See also Vol 2, Pt 4, Ch 4, 1.1 Application 1.1.5.

11. Structural component details including: strut, pod body, bearing supports, bearing end caps, ship’s structure in way of podded propulsion unit integration and a welding Table showing a key to weld symbols used on the plans specifying weld size, type, preparation and heat treatment. The information should include the following:

    • Detailed drawings showing the structural arrangement, dimensions and scantlings.
    • Welding and structural details.
    • Connections between structural components (bolting).
    • Castings' chemical and mechanical properties.
    • Forgings' chemical and mechanical properties.
    • Material grades for plate and sections.

12. Nozzle structure, its support arrangements, together with related calculations for all foreseeable operating and seagoing conditions where the propeller operates in a nozzle (duct), see Vol 1, Pt 3, Ch 3, 5 Fixed and steering nozzles, bow and stern thrust units, ducted propellers.

13. Propeller shaft bearing mounting and housing arrangement details, see also Vol 2, Pt 4, Ch 4, 5.3 Propulsion shafting 5.3.6.

14. Details of propeller shaft and steering bearings, where roller bearings are used supporting calculations are to be submitted, see Vol 2, Pt 4, Ch 4, 5.3 Propulsion shafting 5.3.7 and Vol 2, Pt 4, Ch 4, 5.6 Steering system 5.6.11.

15. Propeller shaft seal details.

16. Details of propeller shaft and pod steering securing/locking and means of aligning the securing/locking arrangements.

17. Cooling systems piping system schematic.

18. Details of any lubricating oil conditioning systems (filtering/cooling/heating) and control arrangements necessary to ensure the continuous availability of the required lubricating oil quality to the propeller shaft bearings.

19. Details of installed condition monitoring equipment.

20. Details of the derivation of any duty factor used in the design of the steering gears.

21. Identification of any potentially hazardous atmospheric conditions together with details of how the hazard will be countered, this should include a statement of the maximum anticipated air temperature within the pod during full power steady state operation, see Vol 2, Pt 4, Ch 4, 2.3 Pod internal atmospheric conditions.

22. Where provided, access and closing arrangements for pod unit inspection and maintenance.

23. Heat balance calculations for the pod unit taking into account electrical thermal rises when the pod is operating at maximum continuous operating conditions, heat transfer and maximum sea-water/air temperatures, see Vol 2, Pt 4, Ch 4, 5.7 Ventilation and Cooling Systems 5.7.4.

24. Details of proposed testing and trials required by Vol 2, Pt 1, Ch 3, 15.2 Testing and trials.

25. Details of emergency steering and pod securing arrangements, see Vol 2, Pt 4, Ch 4, 5.3 Propulsion shafting 5.3.11.

26. Quality plan for electronic control systems and electrical actuating systems.

Figure 4.2.1 Pod co-ordinate system

2.2.2 Where an engineering justification report is required, the following supporting information is to be submitted:

• A Risk Assessment (RA) in accordance with Vol 2, Pt 1, Ch 3, 18 Risk Assessment (RA) is to be carried out, see Vol 2, Pt 4, Ch 4, 2.1 Pod arrangement 2.1.1. The RA is to identify components where failure could cause loss of all propulsion, steering capability or other Mobility systems or Ship Type systems, and the proposed arrangements for preventing and mitigating the effects of such a failure.
• Design standards and assumptions.
• Limiting operating parameters.
• A statement and evidence in respect of the anticipated reliability of any components.

2.2.3 Recommended installation, inspection, maintenance and component replacement procedures, see also Vol 2, Pt 4, Ch 4, 4.1 Pod structure 4.1.2. This is to include any in-water/underwater engineering procedures where recommended by the pod manufacturer. See also Vol 2, Pt 4, Ch 4, 5.5 Bearing lubrication system 5.5.7 and Vol 2, Pt 4, Ch 4, 8 Installation, maintenance and replacement procedures.

2.3.1 Machinery and electrical equipment installed within the pod unit are to be suitable for operation, without degraded performance, at the maximum anticipated air temperature and humidity conditions within the pod unit with the pod operating at its maximum continuous rating in sea water of not less than 32°C after steady state operating conditions have been achieved.

2.3.2 Precautions are to be taken to prevent as far as reasonably practicable the possibility of danger to personnel and damage to equipment arising from the development of hazardous atmospheric conditions within the pod unit. Circumstances that may give rise to these conditions are to be identified and the counter measures taken are to be defined.

2.4.1 The overall strength of the podded propulsion unit structure is to be based upon the maximum anticipated inservice loads, including, the effects of ship manoeuvring and of ship motion, see Table 3.2.1 Ship motions in Vol 1, Pt 5, Ch 3. This is to include the effects of any pod to pod and/or pod to ship hydrodynamic interference effects. The designer is to supply the following maximum load and moment values to which the unit may be subjected with a description of the operating condition at which they occur.

• F _x, Force in the longitudinal direction;
• F _y, Force in the transverse direction;
• F _z, Force in the vertical direction including self weight, in water, augmented by the ship’s pitch and heave motion and flodded volume where applicable, see Vol 2, Pt 4, Ch 4, 4.3 Direct calculations 4.3.3 and Vol 1, Pt 5, Ch 3 Local Design Loads;
• M _x, moment at the slewing ring about the pod unit’s global longitudinal axis;
• M _y, moment at the slewing ring about the pod unit’s global transverse axis;
• M _z, moment at the slewing ring about the pod unit’s vertical axis (maximum dynamic duty steering torque on steerable pods).

The directions of the X, Y and Z axes, with the origin at the centre of the slewing ring, are shown in Figure 4.2.1 Pod co-ordinate system.

2.4.2 Where the maximum forces and moments defined in Vol 2, Pt 4, Ch 4, 2.4 Global loads 2.4.1 cannot be accurately calculated, then an estimate of these loadings is to be stated together with an assessment of the associated error tolerances for the sequences of permitted design manoeuvres, see Vol 2, Pt 4, Ch 4, 1.1 Application 1.1.7. Typically this will include emergency astern manoeuvres, zig zag manoeuvres and pod interaction. Such estimates are to be defined on a load versus pod angle basis. In the case of pod to pod and/or pod to ship hydrodynamic interaction effects, these must be defined for the most severely affected propulsor including cases where pod units are capable of being independently steered.

2.4.3 Where control systems are installed to limit the operation of the podded drive to defined angles at defined ship speeds, this information may be taken into consideration when determining the pod unit loading.

2.4.4 Where pod units are fixed about their Z axis, then maximum global loads, to be used as the basis of the structural appraisal, are to be determined for inflows in 5 degree increments between the extremes of anticipated inflow angle during manoeuvring with ship at full speed and maximum propeller thrust.

2.4.5 The podded propulsor is to be capable of withstanding a blade root failure due to fatigue occurring at the maximum rated output of the podded propulsor without initiating a failure in other parts of the propulsor system. After a blade failure, the podded propulsor is to be capable of reduced power operation in accordance with the manufacturer's instructions.

2.5.1 Where an ice class notation is included in the class of a ship, additional requirements as detailed in Vol 3, Pt 1, Ch 1 Ice Navigation - First-Year Ice Conditions are to be complied with as applicable.