scope:

These Guidance Notes provide overall guidelines on ship vibration excited by the main engine, propeller, or slamming. In these Guidance Notes, the following subjects are considered:

i) Concept Design

ii) Vibration Analysis

iii) Measurements

iv) Acceptance Criteria

The concept design in Sections 2, 3 and 4 provides users with immediate, direct, and concise guidance in effectively dealing with ship vibration in the concept design stage. In attempting to provide a sound and no-nonsense guidelines, these Guidance Notes identify the most serious problem areas that have caused difficulties to the industry, and concentrate on those areas. In the concept design, local vibration is not addressed because detail information is not usually available in the early design stage. Instead, the concept design is focused on those areas that have been known to be of critical importance in avoiding harmful ship vibration.

The vibration analysis in Section 5 provides the FE-based vibration analysis procedure based on first principles direct calculations. The FE-based vibration analysis is recommended to evaluate the design during the detail design stage. If found necessary, the local vibration is to be addressed in the detail vibration analysis. The analysis procedure provides guidelines on FE modeling, engine and propeller excitation, and free and forced vibration analysis. The procedure for calculating slamming excitation can be found in the ABS Guide for Slamming Loads and Strength Assessment for Vessels. Site-specific wave scatter diagram should be used for slamming calculations.

For the assessment of ship vibration performance, the actual vibration levels at the most critical locations are to be measured and evaluated during the sea trials. Section 6 provides guidelines on the vibration measurement procedure on the instrumentation, measurement conditions and locations, data processing and reporting. Section 7 provides acceptance criteria on the vibration limits for human comfort and habitability, local structures and machinery based on international standards and practice in ABS.

The shaft alignment and torsional vibration are not directly addressed in this document. For the requirements of the shaft alignment and torsional vibratory stress, refer to 4-3-2/7 of the ABS Marine Vessel Rules. The overall procedure for ship vibration assessment recommended in these Guidance Notes is shown in 1/5 FIGURE 1.