Following a catastrophic failure of a shaft alternator on a 4,000 tonne clean product tanker the owner approached James Fisher Mimic to investigate how the problem could be avoided in the future.

  • The failure had cost in excess of $90,000 in lost revenue and the cost to repair due to the impact of collateral damage when the alternator failed.
  • The hidden costs, such as increased insurance deductibles and loss of reputation, are harder to quantify.
  • The owner was concerned that a repeat of the defect may occur either on this vessel or sister vessels in the future.

The challenge for JFM was to devise a cost effective monitoring strategy that could predict failures and pre warn the crew so that mitigating action could be taken to avoid a catastrophic failure.

The solution

Following a failure modes analysis, the Mimic Condition Monitoring software system was installed and a monitoring programme created. During the initial set up and whilst conducting a routine performance check, an anomaly on a shaft alternator was identified.Prior to the installation of Mimic these minor changes in performance would have gone unnoticed but Mimic clearly identified a signature pattern different from sister alternators.

A fluctuation in flux field and output combined with a minor increase in vibration and temperature were monitored closely over a 24 hour period following initial identification.This suggested that this alternator had a fault and that it was deteriorating; JFM warned that a failure may occur within 24 to 48 hours.

The owner decided to take the ship out of service.The shaft alternator was inspected and a loose diode cover was diagnosed.A new diode cover was installed and the problem rectified by ship’s staff within 7 hours thus avoiding a catastrophic failure of the shaft alternator whilst incurring minimum downtime.

Cost of Catastrophic Failure:

$60,000 repair costs

$30,000 lost trading revenue

Total Costs:$90,000

Costs Incurred in Planned Repair:

$400 new diode cover

$600 labour

$5,000 lost trading revenue

Total Costs: $6,000


Prior to the Mimic system installation the minor changes in performance had gone unnoticed. Failure to act had resulted in a catastrophic failure of the original shaft alternator and extensive collateral damage.With performance monitoring the onset of failure could be identified early and the risk of failure managed allowing the ship to continue trading with minimal loss of revenue.

The investment in the implementation of the Mimic CM system was justified within 2 months of installation and ongoing performance monitoring continues to add value to the maintenance strategy of the owner’s fleet of ships.