Section 3 Mechanical design requirements
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Code for Lifting Appliances in a Marine Environment, July 2022 - Chapter 9 Machinery - Section 3 Mechanical design requirements

Section 3 Mechanical design requirements

Parent topic: Chapter 9 Machinery

3.1 Allowable stresses

3.1.1 All structural and mechanical components such as winch frames, spoolers, wire tensioners, fairleads, support and drive shafts, except rope drums (see Ch 9, 3.4 Rope drums), are to be designed to comply with the allowable stresses as given in the applicable Chapters of the Code, i.e.:
  1. For launch and recovery appliances for survival craft and rescue boats see:
    1. Ch 3, 1.6 Safety and stress factors 1.6.1; and
    2. Ch 3, 1.8 Davit winches 1.8.2.
  2. For cranes and submersible lifting appliances see:
    1. Ch 4, 2.17 Allowable stress – Elastic failure;
    2. Ch 4, 2.18 Allowable stress – Compression, torsional and bending members;
    3. Ch 4, 2.21 Allowable stress – Plate buckling failure; and
    4. Ch 4, 2.23 Allowable stress – Joints and connections.
  3. For shiplift and transfer systems see:
    1. Ch 5, 5.7 Allowable stresses.
  4. For ro-ro access equipment see:
    1. Ch 6, 2.6 Allowable stress – Elastic failure; and
    2. Ch 6, 2.7 Allowable stress – Plate buckling failure.
  5. For lifts see:
    1. Ch 7, 2.6 Allowable stresses.

3.1.2 Winches for derrick systems will be specially considered.

3.1.3 Proprietary components such as hydraulic motors/pumps will be specially considered.

3.2 Loads

3.2.1 Loads on structural and mechanical components as detailed in Ch 9, 3.1 Allowable stresses 3.1.1 are defined in Ch 1, 2 Definitions and the relevant Sections in the Chapters applicable to the lifting appliance under consideration. All loads on subject components are to be taken as factored loads unless stated otherwise in this Chapter.

3.3 Power supply

3.3.1 The output rating of the power supply is to be designed taking the full load spectrum of the lifting appliance into account, i.e. short-term peak power and long-term nominal power.

3.4 Rope drums

3.4.1 The design of rope drums is to be in accordance with a recognised National or International Standard or a recognised calculation methodology considered acceptable by LR, taking the following criteria into account:
  1. The maximum load under spooling as defined by the selected standard or calculation method;
  2. The maximum holding force from brake or motor;
  3. The corresponding maximum and minimum number of rope layers on the drum;
  4. Where large lengths of rope are to be handled, the capacity of the drum is usually to be designed in such a way as to accommodate the rope on a maximum of three layers of rope. Where a greater number of rope layers are required, suitable spooling arrangements are to be considered (e.g. helical grooving, mechanical spooling device);
  5. The rope end shall be adequately secured to the winch drum. The dimensioning of the rope connection to the drum shall be compatible with the concept of automatic or manual overload protection systems (if fitted) and the performance of their technical protection concept; and
  6. A minimum number of three wraps of steel wire rope is to remain on the rope drum at all times during normal operation.

3.5 Gears and gearboxes

3.5.1 Gears are to be designed in accordance with a recognised National or International Standard such as ISO 6336, and the following details are to be submitted:
  1. Full operational load spectrum;
  2. Test loads of the crane (see Ch 12, 1.6 Cranes and ROV handling systems);
  3. Detailed strength analysis report for both tooth root bending stress and surface stress (also known as Hertzian stress, contact stress or pitting resistance);
  4. Details of the materials applied, including heat treatment, sufficient to establish all of the material parameters used in the stress analysis; and
  5. Details of the manufacturing processes sufficient to establish the accuracy and quality parameters used in the stress analysis.
3.5.2 Gear teeth shall be dimensioned as per the requirements of ISO 6336 and the safety factors shall be as follows:
  1. Root bending stress, SF min ≥ 1,5; and
  2. Surface pressure, SH min ≥ 1,0.

3.6 Shafting

3.6.1 Input, intermediate, output and gearing shafting is to be designed in accordance with a recognised National or International Standard (e.g. DIN 743), which is to be identified in the submitted calculations.

3.7 Shafting connections

3.7.1 Splines, flanges, keys, etc. are to comply with a recognised National or International Standard. Conical and parallel interference fit couplings, flanges, etc. are to be designed for a factor of safety against slippage of 2,0, taking the maximum factored load / torque into account.

3.8 Brakes

3.8.1 In general, brakes shall be designed to a recognised National or International Standard. In addition the following requirements are to be complied with.

3.8.2 Brakes and/or any form of braking due to the drive motor fitted to lifting appliances are to be designed to safely retard, stop and hold the load and/or crane boom and/or any other specific component of a lifting appliance at the full load-speed spectrum. Any braking effect of the drive system shall not be taken into account.

3.8.3 Brakes are to be fitted directly to the output drive component, i.e. a rope drum on a winch or the pinion on a rack and pinion drive. In case any transmission system (i.e. gear box) will be fitted between the brake and the output drive component, the transmission system is to be approved for a load which is equal to the maximum torque applied by the brake.

3.8.4 Brakes fitted to lifting appliances are to be selected for a load of not less than 1,6 times the maximum un-factored load. In case the requirements as detailed in Ch 9, 3.8 Brakes 3.8.2 are not achieved by using a safety factor of 1,6 this safety factor has to be increased accordingly in order to comply with the requirements in Ch 9, 3.8 Brakes 3.8.2.

3.8.5 The minimum expected coefficient of friction (considering unfavourable conditions) is to be applied in the design calculation, which is not to exceed a friction coefficient of 0,3. Details of proof of friction coefficients exceeding this value are to be submitted for consideration.

3.8.6 The boom hoist system on offshore cranes is to be equipped with a secondary brake. Alternative proposals will be specially considered.

3.8.7 The primary mechanical (‘parking’) brake is to be automatically applied after the operating lever is in the ‘off’ or ‘neutral’ position, or on emergency stop application, and immediately upon the failure of the power supply to the motor and/or failure of the control system. Means are to be provided to override the application of the brakes if circumstances require (e.g. emergency lowering of the load), and details of the overriding procedure are to be available during testing for acceptance. The brake action is to avoid sudden dynamic shock loads to the winch and lifting appliance system.

3.9 Clutches

The rating of proprietary clutches fitted to lifting appliances is to provide a factor of safety of not less than 1,5 regarding slippage on the maximum factored load (see Ch 9, 3.2 Loads 3.2.1). Alternatively, operational parameters and detailed plans including materials lists and mechanical properties of the components of the system are to be submitted demonstrating compliance with Ch 9, 3.1 Allowable stresses 3.1.1.

3.10 Bearings

3.10.1 The rating of anti-friction roller bearings is to be verified in accordance with a recognised National or International Standard (e.g. ISO 281).

3.11 Slewing rings

3.11.1 Slewing rings and their bolting are to be in accordance with Ch 4, 2.24 Slewing ring and slewing ring bolting or Ch 4, 3.7 Slew rings (as applicable) or an equivalent recognised National or International Standard.

3.11.2 Where slewing rings employ anti-friction roller bearings, they are to be in accordance with Ch 9, 3.10 Bearings 3.10.1.

3.12 Pressure piping systems

3.12.1 Pressure piping systems are to be designed in accordance with the requirements of Pt 5, Ch 12 Piping Design Requirements, Pt 5, Ch 13 Ship Piping Systems and Pt 5, Ch 14 Machinery Piping Systems of LR’s Rules and Regulations for the Classification of Ships, July 2022. The application of recognised National or International Standards for pressure piping will be specially considered.

3.12.2 Hydraulic pumps fitted to power packs are to be type tested in accordance with the requirements of Pt 5, Ch 19, 7.1 Testing 7.1.3 of LR’s Rules and Regulations for the Classification of Ships, July 2022. The duration of the test is to be representative for the intended life cycle of the pump.

3.12.3 Fabrication of pressure piping is to be carried out as per the requirements given in Ch 13 Requirements for Welded Construction of LR’s Rules for the Manufacture, Testing and Certification of Materials, July 2022 or a recognised National or International Standard for pressure piping.

3.12.4 Air vent arrangements on hydraulic oil tanks are to be such that over or under pressure will remain below the tank design pressure in all conditions of service. The number of pumps which are intended to run simultaneously is to be considered.

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