Making the most of a dry docking

Malcolm Latarche

Malcolm Latarche · 03 July 2019


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Unless they have been granted one of the relatively few extended dry docking notations by class, ships are generally obliged to undergo dry docking at five yearly intervals coinciding with major surveys and also an intermediate dry docking between surveys. Ordinarily, a dry docking is kept as short as practically possible with attention focussed on essential maintenance and repair.

However, technology group Wärtsilä believes that this is the time for ship operators to consider whether they are making the most of the enforced idling of the vessel that is the consequence of a scheduled dry docking. There are many examples of work which could be done at the same time that could significantly improve the environmental and efficiency aspects of the vessel.

Some of those changes are very likely already pencilled in for impending dry dockings. Beginning this year, many ships will need to be taking advantage of scheduled dry dockings to install equipment and systems to meet the ever increasing requirements of MARPOL and other environmental Conventions.

First and foremost there is the 2004 Ballast Water Management Convention. Under its initial terms, all ships subject to it should have been conducting ballast treatment since 2016. However, the troubled journey of the entering into force of the convention is well known and the last installation date for some ships has been pushed back as far as 2024. That means that over the next five years almost all ships will be needing to install a system.

There are differing views on how long it takes to retrofit a ballast treatment system but most suggest that it will occupy all of the normal seven to 14 days of a typical dry docking and in some cases considerably longer; especially if not all of the components have been engineered in advance or if unexpected problems are encountered.

Another aspect of environmental regulation that is even more imminent than the requirement to fit a ballast treatment system is the 2020 reduction on sulphur limits in fuels outside of ECAs. At this point in time it is probably too late for an owner to opt for fitting a scrubber to meet the initial deadline of 1 January 2020, but the impact of the rule change will be felt for many years to come.

It will take time for the full effects of 2020 to be visible. Once the cost of new compliant fuels settles down and the best option becomes clearer, it could well be time for owners to consider if the strategy chosen is still correct. It may well be that fitting a scrubber remains a viable option for many years to come in which case that may be an option for owners.

So far most scrubbers fitted have been open loop types, but if there is a move to limit their use on a wider scale than the few examples of Singapore and parts of China because of the washwater issue, then a conversion to hybrid or closed loop might be a sensible thing to undertake. Again, this could be done during a scheduled dry docking.

After 2020, the next regulatory changes look to be around the EEDI, with Phase 3 being brought forward and a new Phase 4 anticipated. There is also the possibility of a more stringent and mandatory element being added to Ship Energy Efficiency Management Plans (SEEMPs). Improving the efficiency of a vessel can be done incrementally, with some aspects not having a very high capital layout, but with a reasonable payback time.

In June this year Wärtsilä, along with the Netherlands based Maritime Research Institute, MARIN and Italian ship owner Grimaldi, successfully designed an Energy Saving Device (ESD), suitable for use by ships with Controllable Pitch Propellers (CPPs). Following model tests, and subsequent sea trials with Grimaldi’s Grande Portogallo, a 165m Pure Car and Truck Carrier, fuel efficiency gains of 3.5% were confirmed. This translates into a pay-back period of only 1.3 years. The device itself is relatively simple in form and manufacture, and installation during a regular dry docking could be done very easily.

A more capital expensive modification could involve a change of propeller. It is only quite recently that the full power and propulsion systems have been optimised to suit a specific operating mode, rather than having been chosen as separate items suited to a wide range of parameters. The cost savings will vary depending upon how well the initial pairings suit the operational profile of the vessel. A new propeller could save as little as 3 or 5% of fuel consumption, but some changes have resulted in much better performances.

Battery installations are another possibility. Most ships could benefit from this modification in some way. Certainly some ship types make better candidates than others, but almost every ship could produce enough surplus energy at times to charge a battery sufficiently for movements in port. Alternatively, the battery could be charged from shore during port stays helping to lower air pollution and noise nuisance in ports and terminals.

Another environmental upgrade that can be readily undertaken during a regular dry docking is a change of the seals used in a ship’s propeller shaft. Eliminating the risk of pollution entirely is only possible through upgrading to a water lubricated stern tube system. However, many ship owners still operate with oil.

To understand the risk related to using oil lubrication in stern tube systems requires a closer look at the sealing technology. The performance of the seals in oil lubricated stern tube systems is crucial, as costs related to damage caused by seal malfunction can be substantial. The sealing between the stern tube and the propeller shaft has an important role and it has to function efficiently and reliably under harsh and challenging conditions. The outboard propeller shaft seals in oil lubricated solutions serve two main purposes: the prevention of the oil leaking out and polluting the seas, as well as the avoidance of seawater from entering the stern tube system and contaminating the oil.

When water enters the stern tube, it can create water pockets in the oil, or more commonly today with biodegradable oils, it can emulsify with the oil. This compromises the viscosity of the liquid film between the shaft’s running surface and the surface of the bearing. The water content in the oil increases and the load carrying capacity of the oil is reduced, consequently the bearing no longer operates hydro-dynamically and bearing failure occurs. When the film is compromised, the shaft will run on the white metal surface of the bearing, severely damaging both the shaft and bearings. It may overheat the white metal to the extent that its cohesion is affected and the lining is wiped off, causing even more catastrophic damage. Wärtsilä Seals & Bearings has products such as its Wärtsilä Airguard seals which eliminates the risk of leakage by using a void space continually filled with compressed air.

These are just a few examples of the types of work that could easily be undertaken during a dry docking, enhancing the ship’s performance and the owner’s environmental credentials. As the amount of environmental regulations grow, there will undoubtedly be many more.

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