The case of the dynamo

Before asking experts for their opinion, it is necessary to get a basic understanding of what the component does and what happened to it in the past. This is usually not very spectacular as a component is just used from the start the way it should. The dynamos that are in the C32 engine in the Aquila class vessels do however had some important changes.

45 There is one dynamo in each engine. With six engines in operation in the Aquila class vessels in total, this means there are six dynamos in total in operation. This also means that with two spare C32 engines, there are also two spare dynamos. This means there are eight dynamos in total. The words ‘dynamo’ and ‘alternator’ are used interchangeably although these are two (slightly) different devices. A dynamo is just used to generate power in the form of direct current (DC, gelijkstroom), while an alternator generates power with alternating current (AC, wisselstroom). In this report, the component is (wrongly) called ‘dynamo’, but Caterpillar calls it (properly) an alternator. The following preventive maintenance task is advised (Caterpillar, 2010):

“Caterpillar recommends a scheduled inspection of the alternator. Inspect the alternator for loose connections and proper battery charging. Inspect the ammeter (if equipped) during engine operation in order to ensure proper battery performance and/or proper performance of the electrical system. Make repairs, as required. Check the alternator and the battery charger for proper

operation.”

The required time interval for this task is every 5000 operating hours. For the Aquila Class, this is set to 3000 hours in reality because the vessels are expected to be used more intensive. The actual preventive maintenance that is done every 3000 hours, does not always include this whole check. In addition to this maintenance, before starting the engine, the following inspection is required: “Inspect the alternator and accessory drive belts forcracks, breaks, and other damage.” This is also performed in practice.

The name of the 3000 hours maintenance in SAP is ‘Dynamo inspection/cleaning’, which is, as can be concluded from the text above, nothing more than a short visual inspection. Cleaning is only done during revisions. Both experts agree that the preventive maintenance task itself does not change the lifetime of the component in the sense that preventive maintenance will not prevent future failures. However, when doing a thorough inspection, an error can be found. This would be solved by a revision or replacement. Both revision and replacement will make the dynamo ‘as good as new’. Expert ε2 thinks that the current preventive maintenance (visual inspection) should actually be the measuring of the performance of the dynamo (which is also advised by Caterpillar). Because this does not happen (enough), dynamos with improper functionality can live on and fail. Note that Loodswezen does not (always) exactly perform the maintenance that was set by the supplier, although the mechanic indicates that this would be beneficial. Expert ε2 also stated that preventive replacement/revision would be beneficial. This is currently not standard procedure.

In addition to this relatively complicated maintenance tasks there are two more complicating factors. The dynamos were delivered with some teething problems that were twofold:

The dynamo that was delivered by Kvichak did not function the way it was supposed to so it was replaced by a slightly different one from a Dutch supplier. This fact has to be neglected because it cannot be traced when this would have happened and in addition the effects of the change are hard to estimate.

The mounting of the dynamo was not correct in the beginning. For this reason, the forces on the dynamo from the v-belt warped the dynamo, causing the v-belt to slip off. This has also been changed but just like the point above, it cannot be quantified what effects this would have had.

The dynamo in the Aquila class vessels is not used as one would expect. Usually, a dynamo generates power and if it fails, the power is generated by a battery or generator. However, the dynamo in the Aquila class vessels only functions when the battery need to be charged. This situation does not happen if all systems are up and rarely occur during operations. A failure in a dynamo is therefore a hidden failure. It only has to function sporadically. This property also means for Loodswezen that in theory, a vessel is operational, even when the dynamo is on failure (and this is known). This is because the engine will still function properly. If the dynamo would be necessary, the vessel still has

46

another properly functioning engine. In practice, it depends on the crew of the tender whether or not the vessel is in operation.

In Table 4.4, the outcomes of the FMECA are shown. The failure rates are respectively two, one and one per year. This means the failure rate is 4 per year, an MTBF of 365/4 = 91 days.

Failure Mode Cause Condition MTBF Out of service Downtime

FM1 Wrong voltage Hardware failure 0,5 year No 1 day

FM2 Earth Leakage Wear 1 year No 1 day

FM3 Jammed bearing Wear 1 year No 1 day

Table 4.4: Summarized outcome FMECA Aquila Class C32 Dynamo.

It is interesting that the estimated MTBF is just 91 days while the data-driven MTBF, with β = 1,41 and α = 667 (see Table 4.3) is 607 days. This discrepancy can partially be explained by the fact that the FMECA is built up from failure modes, which makes the overall MTBF of a component non- transparent as the MTBF of different failure modes need to be combined. Nevertheless, the difference between the FMECA based MTBF and the data-drive MTBF is so large that one can question the credibility of the FMECA based MTBFs.

In addition to the MTBFs, the down time mentioned here was 1 day, while changing the dynamo (which is nearly always done when it is on failure) just takes about 2 hours (according to the same expert 6 months later).