Fathom World

Mapping the transformation of shipping and the oceans

Marine Environment & FuelsOperations & Management

6 reasons why watching paint dry isn’t as boring as you think

There’s no doubt many in the maritime sector find the thought of talking about marine coatings as exciting as well, watching paint dry.

Yet hull, cargo tank and ballast tank coatings are so important there is a long (and potentially growing) list of regulations on what can and cannot be used.

So here in one location are 6 reasons to watch what refuses to be a dry industry.

1. Tin may be banned, but it is still present. 

Despite the IMO banning the use of organotin tributylin (tin) as an active biocide 10 years ago, it is still present in some coatings.  The IMO permits the ingredient to be used as a catalyst (if organotin content does not exceed the allowable limit of 250mg/1kg of paint) but has been found by academics and scientists to be present in hull coatings, and sometimes as the main ingredient, exceeding this limit.

Increased minnow mortality, growth block and metamorphosis of marine organisms, physical defects and sex changes are just some of the problems the compound has been found to create, even at low levels, according to numerous academic studies.

It is worrying that it is today still permitted as a catalyst when it can cause such biological and environmental upsets. And even more so that it is seemingly used at higher concentrations that should be permitted, which goes unnoticed by the IMO.

Furthermore, a study by Lagerströmet al noted that organotin tributylin was present in layers of coatings from the hulls of boats from more than 20 years ago. Coatings containing it today therefore may have an impact on the environment in future decades.

 

2. A magical ingredient known as Selektope  

Not many hull repelling solutions can claim to deter microorganisms without killing them.  I-Tech, the company that owns and markets special ingredient, Selektope, has managed to do it differently.

A non-metal organic compound, Selektope is based on the same chemistry that creates a tranquilizer drug for vets to use on large animals.  It makes the barnacle larvae fall off the hull coating rather than killing it.  In an academic paper published 2011, this chemistry was shown to not affect fish weight or length and the majority of the parameters were not affected by the compound.

Selektope. Courtesy of I-Tech.

Selektope has a similar effect on larvae.  It repels them but has not shown to have any long-term effects. It makes them hyperactive and encourages further swimming rather than attachment to the hull.

It is however not a coating itself, although it can both replace copper or boost copper-based formulations.

 

3. A war on hull coatings 

The right hull coating can reduce fouling, lower resistance and save fuel.  A medium level of fouling in itself can result in a 52% efficiency loss and a 17% speed loss, says Petter Andersen, principal FPM consultant at DNV GL.

While the most efficient hull will be one that is designed well, paint companies such as Jotun, International and Hempel, have been pushing out new products that claim to increase efficiency by reducing fouling. 

However, heated debates have arisen as a result of these claims as proving performance can be tricky and is currently based on how quickly a coating degrades between drydockings.

Since the debates have intensified, some makers and condition monitoring software firms have agreed a standard, ISO 19030, which was approved last June.

This standard sets out practical measures instead for measuring changes in ship-specific hull and propeller performance and defines a set of performance indicators for hull and propeller maintenance, repair and retrofit activities.

Coatings companies are also coming up with their own standards to prove their coating credibility against competitors. Hempel’s Antifouling Performance Index assess fouling performance on a scale of 1 to 100, taking into account slime, algae and animals.  Jotun, Carbon War Room, and BMT Argoss also have or have proposed systems and methods to measure hull efficiency in various ways.

 

4. Hull blasting 

Using a grinder in preparation for antifouling paint

This is as brutal as it sounds. When a ship needs a hull coating replacement, the current coating is removed by using a copper slag or garnet to ‘blast’ the coating prior to the application of a primer and the new coating.

The abrasive nature of hull blasting has been questioned due to its environmental impact and threat to human health.  It generates dust and chips containing heavy metals and exposes workers and the environment to copper that is contained in paint.

Coating hulls to reduce fuel consumption, which in turn reduces emissions as less fuel is burned is meant to be a cleaner, greener way to shipping.  But removing and replacing hull coatings seems to be a less environmentally sound way of doing so.

 

5. Paints fail because they are not treated as engineering solutions 

Ships need hull coatings, without them they would not last more than a few years and would burn extortionate amounts of fuel due to fouling.  According to Dr. Raouf Kattan, Managing Director, Safinah, hull coatings are an engineering solution but few people treat them this way.

Dr. Kattan told fathom-news that many people will attribute coating failure to poor surface preparation and poor application, but it is far more complicated than this.

In particular, shipyards and shipowners may develop generic paint specifications that are applied to all projects.  Dr. Kattan believes that these may have been grandfathered over many years, with incremental changes making them more and more complex and less fit for purpose.

Each project has its own unique requirements and therefore requires a best match between coating attributes and functionality, and the project needs.  Safinah’s approach focuses on looking at the correct engineering solution to meet the specific vessel’s needs in terms of construction and in service requirements.

Image courtesy of Silverstream. Air covers the full bottom of the vessel and remains in the boundary layer for the entire length of the vessel.

 

6. Paints can help air lubrication 

There is a growing trend in air lubrication. Inserting air into the boundary layer under the hull reduces frictional resistance and can reduce fuel consumption by 5-10% according to Silverstream Technologies.

According to one study in 2016 by MARIN, properties of hull coatings were main parameters in influencing the efficiency improvements of air lubrication. Using a thin layer of super water repellent paint, a thin air film over an underwater surface is formed, preventing the surface from becoming wet.  This air film can also take in air supplied from outside because of the surface tension of the water. Using paint in this way to form the air film reduces frictional drag.

Fukuda et al. suggests that a super water repellent coating combined with air injection is the most attractive method to reducing ship resistance.

 

Fathom-News

editor@fathom-mi.com

About Author