ABS has published a detailed analysis of ship vibration issues which presents the latest developments in vibration analysis, vibration criteria and mitigation measures.
Insights into Ship Vibration Analysis also explores four different real-world cases where vibration issues have been identified, analysed and mitigated.
“ABS has extensive experience of conducting technical investigations into vibration issues.” “/ / 
Source: ABS
ABS has extensive experience of conducting technical investigations into vibration issues.
“ABS’ Insights into Ship Vibration Analysis explores four different real-world cases where vibration issues have been identified, analysed and mitigated.” “/ / 
Source: ABS
ABS’ Insights into Ship Vibration Analysis explores four different real-world cases where vibration issues have been identified, analysed and mitigated.
The report notes that propeller surface forces account for 90% of propeller-caused ship vibrations. They act mainly in the vertical direction on the horizontal part of the ship’s bottom above the propeller. The pressure fluctuations are very sensitive to the amount of intermittent propeller cavitation triggered by the non-uniform wake field.
This non-uniformity can be reduced by changing the stern lines and arrangement of appendages, increasing the clearance between the propeller and the stern bottom plating and changing the propeller geometry. For a conventional stern with skeg and bossing, for example, the vertical tip clearance should be greater than 25% of the propeller diameter.
This is also the case for a single or twin-screw strut stern where, additionally, the shaft inclination angle relative to the baseline should be less than five degrees, and the shaft inclination angle relative to the buttocks angle of the counter should be less than 10 degrees.
As modern vessels become more optimized for improvements to cost, performance and sustainability, new challenges arise, says ABS. Vibration-induced failures are one such challenge that have been hidden by over-designed structures and machinery in the past. As designs have become more optimized, excitation sources from rotating machinery to natural ocean waves are starting to account for fatigue in structures, loss of cargo, malfunctions in machinery and electrical components as well as habitability issues for the crew. Therefore, vibration is now a constraint that must be accounted for in the design.
“This is a challenge that runs to the heart of the ABS mission to advance the cause of safety at sea, and I am proud that we are highlighting critical vibration issues on modern marine structures,” said Gareth Burton, ABS Vice President, Technology. “We took real-world cases where vibration issues have been identified and applied them to the latest developments in vibration analysis. Solutions on mature, existing vessels can be costly. Our goal is to share these findings with industry so that vibration issues are addressed as early as possible.”
The report is available here.
