Sometimes replacing damaged parts doesn’t solve the problem.
A customer approached us with recurring failures of exhaust line dampers and mounting elements on newly built diesel-electric cruise vessels.
Despite frequent replacements, some damping elements were being damaged every few months.
The first step was to check the diesel generators.
Vibration measurements were performed on all generators under different operating conditions. The results showed no abnormalities according to applicable international standards.
So we looked elsewhere.
Measurements along the exhaust lines revealed that the highest vibration levels were concentrated in the first section of the exhaust system — between the diesel engine and the exhaust manifold.
Further multichannel measurements showed that some dampers were exposed to vibration levels exceeding twice the DNV reference limit of 45 mm/s RMS.
But what was causing it?
Detailed spectrum analysis identified dominant frequencies at 20.8 Hz, 25 Hz and 29.2 Hz. These frequencies could be related to engine operating conditions and exhaust gas pulsation, but the high vibration levels suggested another factor: possible resonance of the exhaust structure.
To investigate this, we performed natural frequency measurements using a modal hammering test.
The results confirmed that the frequencies of interest were present in the natural response of the exhaust structure.
But we went one step further.
A 300 kg additional weight was mounted on one of the exhaust lines with the highest vibration levels. The test was performed under the same operating conditions.
The result?
📉 Vibration levels dropped from 84 mm/s to 29 mm/s — below the 45 mm/s DNV reference limit.
This confirmed that changing the dynamic characteristics of the exhaust line could significantly reduce the vibration affecting the dampers.
The problem wasn’t simply the dampers. The real issue was the dynamic behaviour of the exhaust system.
The investigation provided the customer and shipbuilder with objective measurement data that supported the identification of the root cause and helped them develop an appropriate solution for the premature damper failures.
This case is a reminder that effective diagnostics isn’t always about finding what’s broken.
Sometimes, you need to understand why it keeps breaking.