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"Beyond smoothness"

The Naval Architect: June 2016

The EU funded ‘eco-friendly Ship Hull film system with fouling Release and fuel saving properties’ project, or ‘eSHaRk’ as it is more manageably known, is in search of the next efficiency paradigm for coating technologies. Its aim is to commercialise a fouling protection technology that combines the best in fouling protection with an application solution that is environmentally friendly, eases the process of application, and aids the industry pursuit of ever greater drag reduction.

The research project establishes two goals. Firstly, to deliver a method of automated application for an adhesive film coating, and secondly, to develop coating textures that open up new efficiency gains. PPG, the project’s coordinator, will collaborate with a series of industry partners in eSHaRk, including MACtac (an adhesive specialist), Meyer Werft and ND Coatings, VertiDrive (a robotics specialist), and the Hamburg Ship Model Basin (HSVA) to deliver the project’s aims by the end of 2018. Christophe Cheikh, product manager at PPG, says: “The fundamental idea is to develop a siliconised substrate that is industrially engineered to realise optimum fouling release where the surface of the siliconised substrates is textured to have maximum effect on drag reduction.”

The undertaking will combine technological innovations from a variety of fields, harnessing PPG’s new Sigmaglide prototype ­ a self-adhesive fouling release film that is being developed in collaboration with MACtac (Figure 1) ­ and a robotised application technology under development by the Dutch-based automation specialist, VertiDrive.

PPG’s global marketing manager for Marine, Sijmen Visser, explains that the fouling release film innovation answers a practical question: how can the variables interfering with the end state of a coating’s application be removed? He points out that factors such as temperature, humidity, speed of application and curing time, can cost time and efficiency if the coating is imperfectly applied at shipyard or drydock. And so the new technology was developed with an offsite method in mind, ushering in a prefabricated method that ensures the coating will be applied with factory consistency in a one-coat application.

PPG says: “The self-adhesive properties [of the film] allow efficient application without release of solvents on site and do not create any problems of silicone spread [around] the surrounding environment.”

Its developers believe it will improve the control of dry film thicknesses and management of the surface effect, and will deliver a consistent fouling release when compared with conventional spray applications, which offer less control during application. The added control will also allow further optimisation of the surface’s drag reduction capabilities, according to Visser, as the final topography can now be modified to “go beyond smoothness”.

Visser explains that the notion of going “beyond smoothness” has long been witnessed in nature and has been bubbling on the mind of innovators for some time. A shark’s skin, he posits, will allow it to move extremely rapidly in water and has led to the development of hydro-performing swimsuits in the past; why can’t this be applied to commercial ships?

This is reiterated by his colleague, Kees van der Kolk, global technology director of PPG’s Protective and Marine Coatings business, who describes the new film technology as effectively “pulling a speedo on a ship”, increasing its hydrodynamic performance by enhancing its drag reduction. Current expectations of the eSHaRk solution suggest a 10% drag reduction, a doubling of the efficiency provided by Sigmaglide without the application method.

At present, the adhesive film is undergoing tests as a prototype, but eSHaRk’s goal is to upscale and commercialise the technology. Pilot boats have been used as initial test subjects, but the long term intention is that the film will be appropriate for vessels of any type and size. A particular opportunity has been recognised in the newbuild cruise vessel market, where vessels commonly use fouling release technology on their outside hull. Visser says: “Cruiseships are using mainly fouling release for their outside hull, therefore, this technology is quite established in the cruise market and if you then come in with the next innovation in fouling release it is a more natural process.”

Automation technology will therefore be key in the realisation of this goal, as vessels of this size make manual application of the film impractical; manual application of the film occurs at an approximate rate of 100m2 per day, whereas a fully automated, robotised mechanism would allow for the application of roughly 10 times as much per day, says Visser. Progress has been made with an engineered vertical laminator that laminates the foil on the hull with a drying and pre and post heating step. But further mechanisation is still required to ensure the method is fit for shipyard and drydock conditions; the robot now needs to move the laminator from one lane to the next, says Visser.

According to PPG: “Both the number of trials, as well as the size of trial vessels will be increased in order to validate the system thoroughly prior to full scale commercial launch. This validation phase will confirm the benefit for the ship operator in terms of fuel and greenhouse gas.”

eSHaRk will run for three years, by which time the industry partners aim to have a working prototype.

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