Coating care and maintenance
Updated 17 Oct 2019
Some may see coatings as an adornment to the structure or other parts of a ship’s equipment but in reality the various coatings on a ship are a system unto themselves and to function correctly they need regular attention and maintenance. This is essential because any damage to the coating will mean that it is the structure of the ship that is at risk, not just a small area of paint.
Except for occasional in-voyage repair of coatings, application is performed either at the initial building stage or during regular drydockings. This means that the owner is reliant upon firstly classification societies and then on its own superintendents to ensure coatings are applied correctly so that later problems can be avoided. In both cases, the surveyors and superintendents will have many other tasks to undertake and constant supervision is neither feasible nor desirable from a cost perspective.
It should be understood that in almost all cases the coatings themselves are not at fault but the causes will be either inadequate preparation of the steel, the application of the coating or allowing insufficient time for the coating to cure. There will be comebacks upon contractors if coatings fail within a very short space of time but often an inherent problem may take some time to develop allowing claims to be avoided.
Not all coatings are able to be regularly monitored either because they are underwater or inside ballast or cargo tanks. But for those that can be checked, there are signs that those involved in the ship’s maintenance should be able to spot.
Orange peel effect, pinholing, cracks, wrinkles, sags and runs and many more imperfections are easily visible and are indications of incorrect application or preparation and almost always are precursors of trouble ahead, even though there may be no signs of immediate corrosion. If the area is small, it should be within the ability of the crew to rectify it but if large then consideration should be given to pursuing a claim against the contractor.
Sometimes, the problems can be caused by an inappropriate choice of coating given the ambient weather conditions at the yards or the working practices within yards and dry docks. Coatings designed for application within certain temperature or humidity ranges will likely have a shorter life if the conditions prevailing during work do not coincide with the designed conditions.
Shift patterns too can have an effect on the proper application. Where a time between different coats has been specified by the maker, these should be taken into account before work begins. If it is likely that the working pattern would mean an extended time between two coats or perhaps the painters are likely to rush the job to complete it without sufficient time between different coats, then action needs to be taken to ensure that neither case will have a detrimental effect on the coating. If time is limited, then perhaps consideration should be given to opting for an alternative coating.
Almost all manufacturers will quote expected lifetimes for coatings systems but there are very good reasons why these claims need to be considered as guidelines or best case scenarios rather than absolute guarantees. No manufacturer can be held responsible for incorrect preparation, application or use in service but unfortunately these are most frequently the causes for poor coatings performance.
At the time when the concept of PSPC for ballast tanks was first mooted and included into IACS common structural rules, there was much debate over who would undertake inspections and whether there were sufficient qualified inspectors to meet demand. There are industry standards for surface preparation and at the very least the owner should be able to expect that these will be met. Beyond that, the skill of the contractors, environmental conditions with regard to temperature and humidity and how the coatings are allowed to cure before use are all factors that will affect their performance and longevity.
Two fouling protection products that have recently been developed – Micanti and eSHaRk –are very different from conventional coatings and mark a distinct change of direction with regards to application. It remains to be seen if this type of ‘coating on a reel’ and the need to ‘wallpaper’ a ship is a technology that will gain mainstream acceptance but, if it does, then there will be a need for training shipyard personnel in the skills needed and for class surveyors to learn the issues that may arise with regards to preparation and application.
Hull coatings are highly susceptible to damage when navigating in ice so the choice of an appropriate coating is very important. Hard coatings are claimed as being better suited to ice navigation than some of the less resilient products and some manufacturers produce coatings specifically developed with ice navigation in mind.
Operators of ships that regularly operate in the normal winter activity areas such as the Baltic Sea and the St Lawrence Seaway should be fully aware of the problems that ice can cause to coatings. However, use of the Northern Sea Route between Asia and Europe is a relatively new development and may mean that the crews and owners involved have less experience of the potential for ice to damage coatings.
Performance software products
There is one area where coatings manufacturers’ claims are not only used for boosting sales but are often taken literally by regulators and potentially used in formulating regulation that can affect operators. That area is the potential fuel savings and consequent reduction in exhaust emissions claimed for anti-fouling and foul-release products.
Shipping is often perceived wrongly as a dirty industry and the idea that operators could reduce emissions by 5-10% just by applying a coat of paint has been used by some campaigners to highlight the disregard they believe shipping has for the environment. That idea is of course highly flawed but arguments refuting it would likely not be understood by those that make the claim. The shipping industry is fully aware that coatings – or lack of them – can have significant effects on fuel consumption but determining exactly how much is an extremely difficult task.
Developments such as the Energy Efficiency Design Index (EEDI) have caused shipowners and designers as well as regulators to take a new look at how coatings can impact efficiency for good and ill. Although the early stages of the EEDI formula looked only at the design and power of the ship for calculating its CO2 emission score, refinements to it allow for the effect of new and innovative technologies. Included in these are the potential of low-friction coatings.
A ship’s performance tends to deteriorate between drydockings as fouling occurs and shows a marked improvement on leaving drydock. Some of that improvement will doubtless be due to the new coating although engine, turbocharger and propeller overhaul and repair could be much more significant factors.
Changes in operating strategies and working in different geographical regions also make comparison of a ship’s overall performance overtime difficult, meaning the effect attributable to the coatings may be impossible to determine. Even so, some manufacturers have attempted to quantify the savings using software developed by third parties. International Paint and BMT ARGOSS use the BMT SMARTSERVICES system to verify the contribution to vessel performance made by its products and Jotun has similar arrangements with Kyma and Marorka. There are also independent software providers such as Propulsion Dynamics with its CASPER software and Eniram among others.
Propulsion Dynamics’ software was one of the first offerings to be developed in this specialised area and it compares ship performance from hull and propeller fouling with a clean, smooth hull and propeller from sea trials. This generates accurate figures for speed and fuel consumption due to basic roughness and fouling. This initial product has been supplemented with a tool to provide ideal trim based on speed, weather, and loading that does not require installation or calibration of sensors as it is based on a physical model of the vessel.
All of the latest generation of software programs are designed to measure key parameters such as those mentioned above and their developers say that once sufficient data has been collected it is possible to strip out factors alone or in combination to determine the actual effect that one or other has on performance.
Now that coatings manufacturers have developed a means for testing the effectiveness of coatings by way of ISO 19030, the potential for putting quantifiable figures on the energy-saving potential of different types of coatings could impact of the EEDI rating of vessels coated with different products.
The fact that shipowners planning to validate individual manufacturers’ claims for products requires them to install sensors and employ approved software products to record and analyse performance may slow the acceptance of the standard and incorporation into the EEDI formulae for different ship types.
Hull cleaning services
Regardless of the anti-fouling or foul-release coating applied, most ships will suffer a degree of fouling between drydockings that can adversely affect their performance, contribute to non-performance claims under time charters and could be responsible for transferring species between different environments.
Operators of fouled ships have a number of choices open to them including having the hull cleaned by a specialist contractor. The time to the next drydocking and the extra fuel being consumed must be weighed against the cost of cleaning the hull and, for ships with a limited lifespan coating, the possibility of damaging what coating remains is also a factor to be considered.
Ships that have been hard-coated are far less likely to suffer damage from cleaning operations. Manufacturers such as Subsea Industries recommend that cleaning is undertaken regularly if the full benefit of such premium coatings is to be enjoyed. Cleaning can be done by almost any diving contractor with appropriate equipment. Underwater maintenance of Subsea Industries’ Ecospeed is carried out with specially-designed underwater hull cleaning tools that simultaneously remove all fouling and optimise the smoothness of the paint surface. A complete set of complementary equipment was designed in-house to allow divers to clean the flat areas as well as the harder-to-reach parts of the hull without damaging the coating. Sea chests and other nooks and crannies are best cleaned out using underwater high pressure water jet equipment.
This combination makes it possible to have a 100% clean hull after each maintenance session, resulting in the best possible hydrodynamic condition of the underwater hull throughout the service life of the vessel and the removal of any potentially harmful invasive aquatic species that the ship may have picked up. The tools best suited to cleaning hulls are often developed by specialist contractors and sometimes marketed to independent operators.
Most use manually-operated tools but there are a small number of alternatives. CleanHull for example offers efficient hull cleaning, based on its CleanROV (remotely operated vehicle) technology. The company was originally a Norwegian operation but now operates from Singapore and Spain. The CleanROV uses only high-pressure seawater for cleaning and does not harm anti-fouling, which is susceptible to brush damage. It is designed to crawl around a ship’s hull, rotating around its own axis. Cleaning is carried out using water at intermediate pressure, carefully removing any fouling. The machine documents the whole cleaning operation with several cameras, enabling random quality controls of the cleaning process.
UMC is another contractor that has developed its own tools, one of which is the Mini-Pamper, which was initially designed for cleaning acoustically-clad submarines where the absence of any anti-fouling paint meant that device had to deal with extreme marine growth without damaging the fragile surface.
The Mini-Pamper allows the operator to bring a choice of cleaning heads gently into contact with the hull until they are just cleaning and no more. Having selected the correct cleaning pressure, the machine will automatically maintain this level. In 2015 CleanHull and UMC began working together.
A similar service is offered by GAC EnvironHull with its HullWiper ROV. As with the other systems, HullWiper is a brushless cleaning method and it also incorporates a control system that allows the operator to control water pressure and monitor the cleaning process through forward- and aft-facing CCTV cameras. GAC claims that the system is twice as fast as using divers for cleaning hulls and offers a cost savings calculator on its website. The company says the system can clean up to 2,000m²/hr, completing a full hull in just a few hours.
Although hull cleaning is recommended as a means of reducing fuel use and therefore exhaust emissions, it is not an operation that every port authority is prepared to permit. However, HullWiper does not discharge removed residues and harmful materials into the sea. Instead, it collects them with a unique onboard filter unit that is collected by a locally-approved environmental waste disposal company. This cleaning method reduces the risk of cross-pollination of waters with alien species and was a factor in the Australian port of Townsville accepting it for use in local waters in 2018.
Nations reluctant to allow hull cleaning because of risks may need to reconsider if the IMO biofouling guidelines ever become mandatory as, without the ability to clean hulls anywhere ,shipowners would have a legitimate defence against any possible penalties.