Section 4 Lateral vibration

4.1.1 Long unsupported lengths of main propulsion shafting are to be avoided by the fitting of steady bearings at suitable positions. In determining these positions, the Shipbuilder is to ensure that no harmful lateral vibrations are present throughout the speed range, so far as is practicable.

4.2.1 Calculations of the lateral vibration characteristics of shafting systems incorporating cardan shafts are to be submitted to LR for approval, irrespective of the power output.

4.3.1 The calculations in Pt 5, Ch 6, 4.2 Particulars to be submitted 4.2.1, taking account of bearing, oil-film (where applicable) and structural dynamic stiffnesses, are to investigate the excitation frequencies giving rise to all critical speeds which may result in significant amplitudes within the speed range, and are to indicate relative deflections and bending moments throughout the shafting system.

4.3.2 Requirements for calculations may be waived upon request, provided evidence of satisfactory service experience of similar dynamic installations is submitted.

4.3.3 For cardan shafts fitted in the high speed part of thruster drives, lateral vibration calculations are only required for the high speed part of the installation i.e. it is not mandatory to carry out lateral vibration calculations for the complete dynamic system.

4.4.1 Where calculations indicate the possibility of significant lateral vibration responses within the range of ±20 per cent of the M.C.R. speed, measurements using an appropriate recognised technique may be required to be taken from the shafting system for the purpose of determining the need for restricted speed ranges.

4.4.2 The method of measurement is to be appropriate to the machinery arrangement and the modes of vibration which are of concern. When measurements are required, detailed proposals are to be submitted in advance.