Section 5 Machinery design and construction requirements

5.1.1 The requirements detailed in Chapter 1 are applicable.

5.1.2 Means are to be provided whereby normal operation of the podded propulsion system can be sustained or readily restored if one of the supporting auxiliaries becomes inoperative, see also Pt 5, Ch 9, 2.1 Pod arrangement 2.1.1. Consideration shall be given to the malfunctioning of:

• sources of lubricating oil pressure,
• sources of cooling,
• hydraulic, pneumatic or electrical means for control of the podded propulsor.

5.2.1 If gearing is used in the propulsion system then the requirements of Pt 5, Ch 5 Gearing are applicable.

5.3.1 In addition to meeting the requirements of Pt 5, Ch 6 Main Propulsion Shafting and Pt 5, Ch 8 Shaft Vibration and Alignment, the pod propulsion shafting supporting an electric motor is to be sufficiently stiff that both static and dynamic shaft flexure are within the motor manufacturer’s limits for all envisaged operating conditions.

5.3.2 There is to be no significant lateral vibration response that may cause damage to the shaft seals within ±20 per cent of the running speed range. For vibration analysis computations the influence of the slewing ring and shaft bearing stiffnesses together with the contribution from the seating stiffnesses are to be included in the calculation procedures.

5.3.3 As an alternative to the requirements of Pt 5, Ch 6 Main Propulsion Shafting, a fatigue strength analysis of shafting components indicating a factor of safety of 1,5 at the design loads based on a suitable fatigue failure criterion may be submitted for consideration. The effects of stress concentrations, material properties and operating environment are to be taken into account.

5.3.4 With the exception of the propeller connection (requirements stated in Pt 5, Ch 7 Propellers) couplings relying on friction are to have a factor of safety of 2,5 against slippage at the maximum rated torque. In order to reduce the possibility of fretting, a grip stress of not less than 20 N/mm² is to be attained.

5.3.5 The effects of motor short-circuit torque on the shafting system should not prevent continued operation once the fault has been rectified.

5.3.6 The arrangement of shaft bearings is to take account of shaft thermal expansion, misalignment of bearings, shaft slope through the bearings and manufacturing tolerances. Additionally, the influence of the pod deflection on the shaft bearing alignment is to be considered under the most onerous mechanical and hydrodynamic loading conditions.

5.3.7 Propeller shaft roller bearing life calculations are to take account of the following loadings:

• Shaft, motor, propeller and other shaft appendages’ weights;
• Forces due to ship’s motion;
• The propeller-generated forces and moments about the three Cartesian axes related to the shaft; f_x , f_y , f_z , m_x , m_y , m_z , see Figure 9.2.1 Pod co-ordinate system;
• Variance of propeller-generated forces and moments with pod azimuth angle. This load variance should take account of the motor control characteristics;
• Forces due to pod rotation, including gyroscopic forces;
• A predicted azimuth service profile for the pod indicating the proportion of time spent at various azimuth angles;
• Loads due to hydrodynamic interaction between pods;
• Any additional loads experienced during operation in ice conditions (for Ice Class notations);
• Where validation of the above loadings is available, detailed calculations must demonstrate that the bearing life when operating at the normal duty profile will comfortably exceed the time between 5-yearly surveys. Parameters used to justify the bearing life, i.e. those related to oil cleanliness, viscosity limits and material quality are to be quoted.

5.3.8 Where detailed validation of the loadings identified in Pt 5, Ch 9, 5.3 Propulsion shafting 5.3.7. is not available, the calculations for roller bearings are to indicate a bearing life greater than 65,000 hours at the maximum continuous rating of the podded drive taking into account the azimuth angle duty cycle. Any parameters used to justify this life, i.e. those related to oil cleanliness, water contamination and viscosity limits are to be quoted. Proposals for the use of a shaft bearing of life less than 65,000 hours will be considered on application with details of alleviating factors and supporting documentation; however, this bearing life must exceed the time between surveys.

5.3.9 The design of the shaft line bearings is to take account of the maximum and minimum operating temperatures likely to be encountered during both a voyage cycle and, more widely, during the ship's operational life. Furthermore, any anticipated temperature distributions through the bearing components and structures are to be included in the design calculations.

5.3.10 Means are to be provided for detecting shaft bearing deterioration. Where rolling element shaft bearings are used in single pod applications or in pods where the motor power exceeds 6 MW, vibration monitoring of the shaft bearings is to be provided. The bearing monitoring system is to be suitable for the local bearing conditions and is to be able to differentiate from other vibration sources such as propeller cavitation or ship motions.

5.3.11 In multi-podded propulsor systems or ships having at least one pod in association with other propulsion devices and where the individual pod installed power is greater than 5MW, means are to be provided to hold the propeller for an inoperable unit stationary whilst the other pod(s) propel the vessel at a manoeuvring speed of not less than 7 knots. Operating instructions displayed at the holding mechanism’s operating position are to include a direction to inform the bridge of any limitation in ships speed required as a result of the holding mechanism being activated.

5.3.12 Shaft seals for maintaining the watertight integrity of the pod are to be Type Approved to a standard acceptable to LR. The seals are to be designed to withstand the extremes of operation for which they are intended and this is to include extremes of temperature, vibration, pressure and shaft movement.

5.3.13 In single pod installations, the integrity of shaft seals is to be evaluated on the basis of a double failure. In such installations, seal duplication is to be used with indication of failure of one seal being provided.

5.4.1 The requirements of Pt 5, Ch 7 Propellers are to be complied with.

5.4.2 Where propeller scantlings have been determined by a detailed fatigue analysis, based on reliable wake survey data as described in Pt 5, Ch 7, 3.1 Minimum blade thickness 3.1.7 a factor of safety of 1,5 against suitable fatigue failure criteria is to be demonstrated. The effects of fillet stress concentrations, residual stress, fluctuating loads and material properties are to be taken into account.

5.5.1 The bearing lubrication system is to be arranged to provide a sufficient quantity of lubricant of a quality, viscosity and temperature acceptable to the bearing manufacturer under all ship operating conditions.

5.5.2 In addition to the requirements detailed in this Section, the requirements of Pt 5, Ch 14, 8.1 General requirements, Pt 5, Ch 14, 8.5 Emergency supply for propulsion turbines and propulsion turbo-generators, Pt 5, Ch 14, 8.7 Filters and Pt 5, Ch 14, 8.9 Cleanliness of pipes and fittings are to be complied with.

5.5.3 For systems employing forced lubrication, the sampling points required by Pt 5, Ch 14, 8.13 Deep tank valves and their control arrangements 8.13.6 are to be located such that the sample taken is representative of the oil present at the bearing.

5.5.4 For lubricating oil systems employing gravity feed, the arrangements are to be such as to permit oil sampling and oil changes in accordance with the manufacturer's instructions for the safe and reliable operation of the propulsion system.

5.5.5 Where continuous operation of the lubricating oil system is essential for the pod to operate at its maximum continuous rating, a standby pump in accordance with Pt 5, Ch 14, 8.2 Pumps 8.2.2 is to be provided. In such systems, provision is to be made for the efficient filtration of the oil. The filters are to be capable of being cleaned without stopping the pod.

5.5.6 Where bearings are grease lubricated, means are to be provided for collecting waste grease to enable analysis for particulates and water. The arrangements for collecting waste grease are to be in accordance with the pod manufacturer’s recommendations. Alternative arrangements which demonstrate that bearings are satisfactorily lubricated will be considered.

5.5.7 Pipework conveying lubricating oil is to be sited such that any possible leakage from joints will not impinge on electrical equipment, hot surfaces or other sources of ignition, see also Pt 5, Ch 13, 2.9 Miscellaneous requirements 2.9.3

5.5.8 The procedures for flushing the lubrication system are to be defined. This procedure is to embrace the following conditions:

1. Initial installation.

2. Post maintenance situations.

3. Major dry-docking refits.

See Pt 5, Ch 9, 9 Installation, maintenance and replacement procedures.

5.6.1 The requirements of Pt 5, Ch 19 Steering Systems are to be complied with where applicable.

5.6.2 The arrangement of podded propulsion units is to be such that the ship can be satisfactorily manoeuvred to a declared performance capability. The operating conditions covered are to include the following:

1. Maximum continuous shaft power/speed to the propeller in the ahead condition at the declared steering angles and sea conditions.

2. Manoeuvring speeds of the propeller shaft in the ahead and astern direction at the declared steering angles and sea conditions.

3. The stopping manoeuvre described in Pt 5, Ch 1, 5.2 Sea trials 5.2.2.(b).

4. All astern running conditions for the ship.

5. Manoeuvring in ice where ice class is required.

5.6.5 The auxiliary steering gear is to be:

1. Capable of being brought speedily into action in an emergency; and

2. Of adequate strength and capable of changing the direction of the ship’s podded propulsion unit from one side to the other in accordance with the declared steering angle limits at an average turning speed of not less than 0,5 deg/s, with the ship running ahead at one half of the maximum ahead service speed or 7 knots, whichever is the greater; and

3. Operated by power for ships having propulsion power of more than 2500 kW per podded propulsion unit and for all ships, where it is necessary to meet the requirements of Pt 5, Ch 9, 5.6 Steering system 5.6.5.(b).

5.6.6 In addition to the requirements in Pt 5, Ch 9, 2.1 Pod arrangement 2.1.1, for ships fitted with a single steerable podded propulsion unit, where the main steering gear comprises two or more identical power units and two or more identical steering actuators, auxiliary steering gear need not be fitted provided that the steering gear:

1. In passenger ships capable of satisfying the requirements in Pt 5, Ch 9, 5.6 Steering system 5.6.4.(a) while any one of the power units is out of operation;
2. In cargo ships capable of satisfying the requirements in Pt 5, Ch 9, 5.6 Steering system 5.6.4.(a) while operating with all power units; and
3. Is arranged so that after a single failure in its piping system or in one of the power units, steering capability can be maintained or speedily regained.

5.6.7 For ships fitted with more than one steerable podded propulsion unit, where each main steering system comprises two or more identical steering actuating systems, auxiliary steering gear need not be fitted provided that each steering gear:

1. In passenger ships capable of satisfying the requirements in Pt 5, Ch 9, 5.6 Steering system 5.6.4.(a) while any one of the power units is out of operation;
2. In cargo ships capable of satisfying the requirements in Pt 5, Ch 9, 5.6 Steering system 5.6.4.(a) while operating with all power units; and
3. Is arranged so that after a single failure in its piping or in one of the steering actuating systems, steering capability can be maintained or speedily regained (e.g. by the possibility of positioning the failed steering system in a neutral position in an emergency, if needed). Consideration will be given to alternative arrangements providing equivalence can be demonstrated.

The above capacity requirements apply regardless of whether the steering systems are arranged with shared or dedicated power units.

5.6.8 The steering gear for podded units used for dynamic positioning applications with an associated class notation, is to be capable of a turning speed of not less than 9 deg/s.

5.6.9 Steering arrangements, other than of the hydraulic type, may be accepted provided that there are means of limiting the maximum torque to which the steering arrangement may be subjected.

5.6.10 Geared arrangements employed for steering are to consider the following conditions:

• A design maximum dynamic duty steering torque, M _z, see Pt 5, Ch 9, 2.4 Global loads 2.4.1;
• A static duty (≤10³ load cycles) steering torque. The static duty steering torque should not be less than M _w, the maximum torque which can be generated by the steering gear mechanism.

The minimum factors of safety, as derived using ISO 6336 Calculation of load capacity of spur and helical gears, or a recognised National Standard, are to be 1.5 on bending stress and 1,0 on Hertzian contact stress. The use of a duty factor in the dynamic duty strength calculations is acceptable but the derivation of such a factor, based on percentage of time spent at a percentage of the maximum working torque, should be submitted to LR for consideration and acceptance.

5.6.11 Slewing ring bearing capacity calculations are to take account of:

• Pod weight in water;
• Gyroscopic forces from the propeller and motor;
• Hydrodynamic loads on pod; and
• Forces due to ship's motions.

The calculations are to demonstrate that the factor of safety against the maximum combination of the above forces is not less than 2. The calculations are to be carried out in accordance with a suitable declared standard.

5.6.12 Means of allowing the condition of the slewing gears and bearings to be assessed are to be provided.

5.7.1 Means are to be provided to ensure that air used for motor cooling purposes is of a suitable temperature and humidity as well as being free from harmful particles.

5.7.2 Cooling water supplies are to comply with Pt 5, Ch 14, 7 Engine cooling water systems. See also Pt 6, Ch 2, 9.6 Machine enclosure

5.7.3 On single podded installations, a standby cooling arrangement of the same capacity as the main cooling system, is to be provided and available for immediate use.

5.7.4 For pods having an electric propulsion motor but no active cooling system, heat balance calculations as required by Pt 5, Ch 9, 2.2 Plans and information to be submitted 2.2.1.(w) are to demonstrate that the pod unit and associated systems are able to function satisfactorily over all operating conditions, see Pt 5, Ch 1, 3.5 Ambient reference conditions

5.8.1 Unless the electrical installation is suitable for operation in a flooded space, means are to be provided to ensure that leakage from shaft bearings or the propeller seal do not reach the motor windings, or other electrical components. Account is to be taken of cooling air flow circulating within the pod unit.

5.8.2 Where the design of a pod space has a requirement to be maintained in a dry condition, two independent means of drainage are to be provided so that liquid leakage may be removed from the pod unit at all design angles of heel and trim, see Pt 5, Ch 1, 3.6 Ambient operating conditions

5.8.3 Pipework conveying leakage from the pod is to be sited such that any leakage from joints will not impinge on electrical equipment, see also Pt 5, Ch 13, 2.9 Miscellaneous requirements 2.9.3

5.9.1 Hydraulic actuating systems are to comply with Pt 5, Ch 14, 9 Hydraulic systems and Pt 5, Ch 19, 3 Construction and design as applicable.