Section 2 General requirements

2.1.1 In general, for a ship to be assigned an unrestricted service notation, a minimum of two water jet systems is to be provided where these form the sole means of propulsion. For ships where a single water jet system is the sole means of propulsion, a detailed engineering and safety justification is to be evaluated by LR, see Pt 12, Ch 2, 2.3 Calculations and information 2.3.22. This evaluation process will include a risk analysis, using a recognised technique to verify that sufficient levels of redundancy and monitoring are incorporated in the water jet unit’s essential support systems and operating equipment.

2.1.2 Water jet propulsion units are to be capable of continuous operation between their maximum and minimum output power rating at specified operating conditions, see Pt 12, Ch 1, 3 Materials and within the operational service profiles defined by Pt 12, Ch 2, 2.3 Calculations and information 2.3.11 and Pt 12, Ch 2, 2.3 Calculations and information 2.3.12.

2.1.3 It is the Shipbuilder’s responsibility to ensure that all of the installed equipment is suitable for operation in the location and under the environmental conditions defined in Pt 12, Ch 1 Propellers. Where anticipated environmental conditions are outside these limits or where additional conditions are to be considered, such as vibration and impulsive accelerations, requirements and details of compliance are to be submitted to LR.

2.2.1 Plans, in triplicate, and information as detailed below and in Pt 12, Ch 2, 2.3 Calculations and information and Pt 12, Ch 2, 2.4 Failure Mode and Effects Analysis (FMEA) are to be submitted for consideration.

2.2.2 General arrangement plans showing details of the following:

1. Shafting assembly indicating bearing positions.

2. Steering assembly.

3. Reversing assembly.

4. Shaft sealing arrangement assembly.

5. Longitudinal section of the complete water jet unit.

2.2.3 Detailed and dimensioned plans indicating scantlings, materials of construction and, where applicable, surface finish of the following:

1. Arrangement of the system, including the intended method of attachment to the hull and building-in, tunnel geometry, shell openings, method of stiffening, reinforcement, etc.

2. All torque transmitting components, including the shafting system, impeller and stator if fitted.

3. Steering components, together with a description and line diagram of the control circuit. This is to include steerable exit water jet nozzles where fitted.

4. Components of the retractable buckets where these are used for providing astern thrust.

5. The bearing or bearings absorbing the thrust and supporting the impeller, together with the method of lubrication.

6. Details of any shafting support or guide vanes used in the water jet system.

2.2.4 Schematic plans of the lubrication and hydraulics required for steering/reversing systems, together with pipe material, relief valves and the working pressures required.

2.3.1 Strength calculations based on fatigue considerations incorporating the maximum continuous torque rating and the most ‘onerous’ operating condition, see Pt 12, Ch 2, 2.3 Calculations and information 2.3.12, including any short-term high power operation, and including the effects of mean and fluctuating loads, transitory loadings, residual stress allowances, and stress raisers, for the following components:

1. Impeller, stator and any bolting arrangements supporting propulsion or steering loads.

2. Shaft supports and coupling arrangements.

3. Inlet guide vanes, if fitted.

4. Steering components, including the lugs of steerable nozzles where fitted.

5. Retractable buckets and associated mechanisms which are used to provide astern thrust. A calculation of the hydrodynamic transient loads is to be made for each design and is to include the full ahead to full astern condition. The calculation procedure used is to be supported, where possible, with full scale or model test data, or satisfactory service experience, to validate the design method.

2.3.2 Calculations supporting the connection method of the impeller to the shaft including details of the fit, push-up, securing, bolting arrangements, etc. In addition, where lengths of shafts are joined using couplings of the shrunk element type, full particulars of the method of achieving the grip force.

2.3.3 Calculations relating to the design of the shaftline as evidence of compliance with Pt 11, Ch 2 Shafting Systems.

2.3.4 Torsional vibration calculations of the complete dynamic system in accordance with the relevant requirements included in Pt 13, Ch 1 Torsional Vibration.

2.3.5 Shaft lateral vibration calculations where required by Pt 13, Ch 3 Lateral Vibration.

2.3.6 Calculations of the tunnel strength and supporting structure.

2.3.7 A calculation to determine the stresses within the impeller blade.

2.3.8 A calculation of the blade natural frequency for the impeller blades.

2.3.9 A calculation of the relative blade passing frequency between the rotor and stator blades.

2.3.10 The value of the fluctuating stresses during one revolution of the impeller and from transient loadings.

2.3.11 Details of the power/speed range of operation, indicating the maximum continuous torque rating, together with the associated thrusts; this information may be presented in the form of a characteristic curve for the water jet.

2.3.12 The water jet thrust for the assessment of the strength condition being considered is to be as follows:

1. For ships which are intended to operate predominantly in a free-running condition and at steady service conditions, the water jet thrust is to correspond to the absorption of the maximum continuous shaft power and corresponding revolutions per minute, giving the maximum torque for which the shaft system is approved.

2. For ships which are designed for several operating conditions, the maximum thrust associated with these conditions and the absorption of the corresponding power, in addition to the maximum continuous powering condition, are to be used in the calculation.

3. The justification for the thrust selected is to be submitted for consideration in the approval process and this is to include the ship type and the ship speed at the conditions considered.

2.3.13 A justification that the water jet system will meet the self-priming criteria, see Pt 12, Ch 2, 3.1 General 3.1.6.

2.3.14 Specifications of materials and NDE procedures for components essential for propulsion and steering operation and, in the case of the impeller and stator, the yield strength and the fatigue characteristics of the material intended for their manufacture.

2.3.15 A detailed weld specification where an impeller has welded blades.

2.3.16 Full details of the means of corrosion protection in the case of carbon or carbon manganese steel shafts. Alternatively, where it is proposed to use composite shafts, details of the connections at flanges, materials, resin, lay-up procedures, quality control procedures and documentary evidence of fatigue endurance strength is to be provided.

2.3.17 Dry impeller mass and polar moment of inertia.

2.3.18 The prime mover type and designation.

2.3.19 Details of the control engineering aspects of the system design in accordance withPt 16, Ch 1 Control Engineering Systems.

2.3.20 The tolerance specification, agreed between the manufacturer and the Shipbuilder or Owner, to which the components of the unit are to be manufactured is to be defined together with a justification.

2.3.21 Details of the water jet’s loading reactions together with the positions of application within the hull and is to include the maximum applied thrust, tunnel pressures, moments and forces imposed on the ship.

2.3.22 The water jet unit’s rated flow and head.

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

• A Failure Mode and Effects Analysis report (FMEA), see Pt 12, Ch 2, 2.4 Failure Mode and Effects Analysis (FMEA).
• Design standards and assumptions.
• Limiting operating parameters.
• A statement and evidence in respect of the anticipated reliability of any non-duplicated components.

2.3.24 Recommended installation, inspection, maintenance and component replacement procedures. This is to include any in-water engineering procedures where recommended by the water jet manufacturer.

2.3.25 All transient loads which the steering unit is likely to experience from manoeuvring, accelerating, decelerating and the sea conditions.

2.4.1 An FMEA is to be carried out where a single water jet system is the ship’s sole means of propulsion, see Pt 12, Ch 2, 2.2 Plans to be submitted 2.2.3. The FMEA is to identify components where a single failure could cause the loss of all propulsion and/or steering capability and the proposed arrangements for preventing and mitigating the effects of such a failure.

2.4.2 The FMEA is to be carried out using the format presented in Table 22.2.1 Failure Mode and Effects Analysis of the Rules and Regulations for the Classification of Ships, hereinafter referred to as the Rules for Ships, or an equivalent format that addresses the same reliability issues. Analyses in accordance with IEC 60812 Analysis for System Reliability – Procedure for Failure Mode and Effects Analysis, or the IMO Code of Safety for High Speed Craft, 2000, Annex 4 – Procedures for Failure Mode and Effects Analysis, would be acceptable.

2.4.3 The FMEA is to be organised in terms of equipment and function. The effects of item failures at a stated level and at higher levels are to be analysed to determine these effects on the system as a whole. Actions for mitigation of the effects of failure are to be determined, see Pt 12, Ch 2, 2.4 Failure Mode and Effects Analysis (FMEA) 2.4.1.

2.4.4 The F.M.E.A is to:

1. identify the equipment or sub-system and mode of operation;

2. identify potential failure modes and their causes;

3. evaluate the effects on the system of each failure mode;

4. identify measures for reducing the risks associated with each failure mode;

5. identify measures for preventing failure; and

6. identify trials and testing necessary to prove conclusions.

2.4.5 At sub-system level it is acceptable, for the purposes of these Rules, to consider failure of equipment items and their functions. It is not required that the failure of components within that equipment item be analysed, see Pt 5, Ch 22, 2.1 General 2.1.5 of the Rules for Ships.

2.4.6 Where a FMEA is used for consideration of systems that depend on software-based functions for control or co-ordination, the analysis is to investigate failure of the functions rather than a specific analysis of the software code itself.