In-depth | PAINTS


Graph showing fuel consumption before (blue) and after (red) dry-docking.


Te gradient of the two lines, showing the Te owner/operator will then normally


select a vessel in their fleet of the correct age range being already scheduled for such surface preparation, regardless of system selected. This would normally be 10-15 years from new-build with an underwater paint system that is quite rough from several dockings with spot blasting and repairs. So the full blast will bring the hull condition from the worst to the very best, from rough and possibly fouled to very smooth and clean. We know that the improvement in


fuel consumption from this surface preparation can be in the range from 25-40%, depending on the prior condition. With this in mind and the fact that the above fuel saving for the biocide free hull systems are, in many cases, guaranteed for only one year after docking, it is quite simple to understand how 7-10% fuel savings can be guaranteed. Even in our performance analysis linked to the positive effects on fuel consumption originating from a maintenance


repair docking we see positive


effects in the range of 20% improved fuel performance. Te graph above is an example of how


fuel savings are sometimes “proven” by measurements of fuel oil consumption in a period before (blue markers and line) and after (red markers and line) docking. The fuel oil consumption resulting from both biocide containing (blue) and biocide free (red)


are


plotted in the same figure and on top of each other. There is a clear


reduction in fuel


consumption, in this case approx. 10%. This is correct if fuel consumption is measured based on average figures 12-24 months before and 12-24 months aſter docking. At this point it is easy to forget that the fact that surface preparation by full blasting in dock contributes to an even larger reduction in fuel consumption. In the above example the savings from blasting of the hull coatings resulted in as much as 22% fuel saving.


Light and dense slime on the hull of a container ship.


development of fuel oil consumption over time are also similar, indicating that a freshly applied biocide free technology has the same increase in fuel oil consumption as a 12-15 year old primer system with a biocide containing antifouling as the last coats. In the above example this biocide containing antifouling would not be a high quality product but a medium to low quality one based on the rather steep increase in fuel consumption. Have we just created an illusion based on what we wanted the above theoretical example to prove, or is it based on solid facts? Tat is the one of the vital questions that the reader should ask him or herself. Te irony is that customers, academics and


also environmental bodies are led to believe that the biocide free products are only good for the environment. Paint makers have built this image by statements focusing on how much CO2


that could have been saved if all


vessels used their technology. Jotun is of the firm belief that many customers now realise that this is far from founded on operational experience and that the individual vessel’s fuel consumption actually has a significantly larger increase with the biocide free than with most biocide containing products. Tis increase in fuel consumption is mostly due to the light and dense slime, as shown in the pictures below, showing performance on container vessels. If these large container vessels are unable to


benefit from today’s versions of the biocide free technologies then it is hard to imagine what trade, speed and type of vessel that could have fuel saving benefits.


18


The Naval Architect July/August 2011


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