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When predictive maintenance is all at sea

08 September 2015

Condition-based maintenance can help ship builders and operators enhance machinery performance and boost profitability, says Gavin Coull.

Any industry that uses a lot of independent machines can derive huge benefit from condition-based maintenance (CBM). A good example of this is shipbuilding and repair, which is under as much financial pressure as any other part of the manufacturing sector.

CBM is a tried and trusted technique in manufacturing. It helps improve overall machine efficiency and ensures timely, accurate repair of machines – keeping a constant watch on their condition and identifying errors before they cause problems. Most importantly, it helps reduce machine operating and maintenance costs.

Ship owners are also striving to protect operating margins in a number of ways, such as by optimising trade routes, reducing cruise speeds and improving fuel efficiency. They may see CBM as an unnecessary expense, but the reverse is true. By investing in CBM, ship owners and operators can benefit from efficiencies that arise from greater machine reliability – and increase the number of days that each vessel remains at sea.

A ship used in the offshore sector is brought into dry-dock every two and a half years on average for overhauls of on-board machinery, and every day in dry-dock represents lost revenue. 

The ship industry’s take-up of CBM has been relatively slow for a number of reasons: natural conservatism; reliability; stringent regulations; and tough economic conditions. However, this attitude is beginning to change, as operators are seeing the enormous benefits that CBM can deliver.

Risk probability
At last year’s International Conference on Maritime Technology held in Glasgow, researchers from Strathclyde University presented details of a mathematical model to determine the mathematical probability of parts on a ship failing. The model relies on data received from an array of on-board devices such as vibration monitors, thermal imagers and both acoustic and ultrasonic monitors.

The study looked at the main engine and its sub-systems, including the lubrication, starting and cooling systems. Detailed analysis of the sub-systems provides a more accurate risk assessment of component failure. In future, the researchers intend to improve the model further by identifying links between parts of the system – such as bearing and pistons, or shaft and bearing.

While this is still at the research stage – and is not ready to be deployed – it does underline the importance of installing CBM on ships. And that’s something that is already happening. Investing in automated CBM systems could delay the need for major overhauls – meaning that a ship will undergo fewer major maintenance operations during its lifetime and spend more time at sea.

Routine repairs can also be carried out with more confidence, and be planned so that they can be completed while vessels are in port or at sea, so that they do not affect normal operations. For example, a damaged gear tooth in a thruster’s lower gear box may go undetected during the dry-dock and maintenance period without CBM. However, if CBM techniques were used, the inspection and repair of this gear tooth can take place during a scheduled docking period, removing the need for a ship being docked for unscheduled repairs.

CBM data can be gathered in a number of ways. On-board engineers can use handheld devices to carry out portable data collection, or use online systems for critical equipment, where fixed sensors mounted in dangerous or difficult-to-access areas are hard-wired back to a central on-board control room. Data can therefore be analysed by the ship's engineers or, more commonly for critical equipment, be transmitted to a shore-based facility for interpretation by experts in a remote location.

Bandwidth issues
Of course, there are some key differences that do not translate directly from the manufacturing to the marine sector. One is the availability of network or satellite bandwidth.

Condition monitoring naturally generates very large amounts of data. In a manufacturing environment, with on-site analysis, data overload is rarely a problem. On-board ship, once the vessel is out of reach of land-based communications networks, it is impractical to send such high volumes of data over satellite links – especially if it has to compete for bandwidth with voice or other more critical communication. Therefore, information must firstly be carefully analysed and filtered, with only the most relevant data being transmitted for on-shore analysis. 

It’s not just maintenance data that’s important; CBM is increasingly moving into performance monitoring. Ship owners require real time data such as fuel consumption and emission levels to optiise their operations, and new methods are emerging to help meet these needs.

For example, BVI’s Turbulo BlueMon is an emission monitoring system that records everything in one place. By linking to GPS position data, the system helps compliance with marine MARPOL conventions, so that if a ship approaches an area with higher emission standards a warning can be sent to the bridge so that emission levels can be re-checked. Data remains available for 24 months, allowing later verification of compliance.

This and other systems are effectively filling in the ship’s logbook automatically – the kind of operation that is likely to become far more common in future. Fitting this technology to an entire fleet would allow a ship owner to benchmark its environmental performance against industry standards, or identify the best performing crews and vessels.

A further benefit of centralised data collection is that it helps overcome a common trend within the marine industry – that of engineers rotating between ships, with knowledge of individual vessels inevitably being lost as staff move on.

Looking to the future
The marine industry will not adopt CBM overnight. The main focus of marine engineers is reliability as a means of optimising vessel availability; this has historically been carried out using visual or time-based maintenance inspections, so changing the culture will take time.

Perhaps the biggest challenge faced by marine engineers is managing multiple on-board machines; indeed, in many instances there are so many machines on each ship, from so many different suppliers, that it resembles a floating factory.

In order to manage this, ship owners and operators will increasingly need to find strategic partners that can offer ship-wide, fleet-wide condition monitoring – enabling them to increase the time that each vessel spends profitably at sea.

Gavin Coull is key account manager, Marine at SKF

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