General coatings maintenance overview
Coatings may appear 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.Safety
When working with coatings, both in preparation and application, care should be taken to ensure any safety instructions are adhered to. There are other safety issues for an operator to consider when crew are tasked to work on coatings. These include use of PPE and more generally applying safe practices for working at heights, overside and in enclosed spaces. The latter can be especially dangerous considering the potential for low oxygen levels to begin with and VOC released from the coating being applied.
Cutting or welding of any painted surface should take into account the properties of the paint used. Failure to do this can result in the release of harmful vapours and in most cases a fire risk. Eye protection should always be worn when working in painted areas especially if preparing for repainting because of the risk of paint chips striking eyes. When preparing old paint surfaces, the danger of dust from the paint should not be underestimated. Rubbing down wet is a sensible precaution. PPE must be worn when using paint strippers because of their caustic naturHull cleaning services
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 of such coatings 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, but some coatings makers have developed proprietary systems that use specially designed underwater hull cleaning tools that simultaneously remove all fouling and optimise the smoothness of the paint surface. 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 hull cleaning service providers use divers with manual tools but there are a small number of alternatives that make use of robotic vehicles. Depending upon the contractor these specialist vehicles can employ water pressure or brush systems. When equipped with cameras, these devices also contribute to recording the extent of fouling before and after the cleaning which may prove useful if the condition of the fouling is queried by PSC inspectors.
A system recently introduced by Jotun, combines a suitable anti-fouling coating with a ship-mounted robotic device. The HullSkater robot is intended to eb used regularly to monitor fouling and to remove any at an early stage of growth. The system is deployed by the crew but operated remotely by a trained Jotun operator using a 4G communications link
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.
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.Performance Software
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. 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 typeISO 19030
Mandatory coatings, their application and maintenance are not yet things that operators need to worry about but since 1 January 2013 ships have been required to implement a Ship Energy Efficiency Management Plan (SEEMP). Each ship’s implementation date was linked to its survey cycles and all ships should now have a SEEMP in place.
According to the IMO, poor hull and propeller performance is often due to fouling and accounts for around 10% of the world fleet’s fuel consumption. This costs owners an estimated $30Bn in additional fuel costs annually.
Since hull fouling has an obvious detrimental effect on a ship’s efficiency it is evident that the matter of anti-fouling should be covered in its SEEMP. Taking voluntary action on biofouling is something that many operators do as a matter of course but formalising procedures could make a ship more attractive to potential charterers and an obvious concern for environmental matters is likely to influence official inspectors in a positive way.
The various claims made by makers of hull coatings with regard to performance and fuel saving potential have long been treated with some jaundiced suspicion by operators and with no universal method for measuring the savings achieved this is understandable.
However, the development of ISO 19030 as a new standard, called ‘Measurement of changes in hull and propeller performance’, is considered a major step forward. This standard complements ISO 15016 (for sea trials) focusing on in-service monitoring.
ISO 19030 uses a three-tiered approach, reflecting different levels of accuracy.
ISO 19030 was finalised in 2016 following three years of development by a wide range of industry stakeholders including coating and propeller manufacturers, academics, shipowners and data analysts. It became effective in March 2017 and enables shipowners and operators to compare hull and propeller solutions and to select the most efficient option for their vessels and fleets.
As well as outlining general principles for measuring changes in hull and propeller performance, the standard also defines a set of performance indicators for hull and propeller maintenance, repair and retrofit activities. It is not mandatory and for it to apply to any product, the ship operator must establish a monitoring regime that may well deter many operators from making use of the standard.
The general principles outlined, and the performance indicators defined are applicable to all ship types driven by conventional fixed pitch propellers, where the objective is to compare the hull and propeller performance of the same ship to itself over time. Support for additional configurations such as variable pitch propellers or podded propulsion systems will, if justified, be included in later revisions.
ISO 19030 is not the only initiative aimed at verifying the performance of antifoulings. In 2018, classification society DNV GL announced that along with coatings manufacturer PPG it had identified a market demand for methodologies that go beyond ISO 19030. The two organisations said that as more owners invest in more sophisticated sensors, tools and systems to collect operational data, performance can be measured more precisely over time. PPG will provide data from the many vessels using its products and use DNV GL’s Fleet Performance Management Platform ECO Insight to analyse the data.