Alternatives to Antifoul


November 22, 2016

Alternatives to Antifoul

Findings & reserach relating to Foul Release Boat Paints

Introduction:

Recently, AquaMarine FRC has been working on areas of research and collating new information regarding the benefits of foul release boat paints over traditional antifouling. Interestingly, during our research we located a piece of earlier research conducted by Newcastle University back in 2001. The results of the tests, taken long-before the increased interest in foul release is still significant some 15 years later. So much so that we decided to remind everyone that foul release really has proven its worth since it was first considered an alternative to antifoul.

The development and popularity of foul release boat coatings has gained increasing momentum in recent years, persevering through the dragging comparisons of its traditional, yet outdated predecessor; antifoul coatings.

Besides the eco-friendly and cost-effective benefits of foul release coatings over antifoul, one of the most important applications of a product like AquaMarine FRC is its overall ability to increase the speed of boats due to its ultra-smooth low friction surface, and effective reduction of fouling settlements through a regular cleaning maintenance programme.

More than a decade ago in the comprehensive study conducted in 2001, reliable results and evidence were found supporting the advantages of foul release coatings compared to antifoul relating to drag, roughness and other contributing factors. These findings showed promise for an ecological, more successful alternative to the long-established biocide containing antifoul treatment method. Together with the recent facts & figures acquired from case studies conducted with our own trials, we can elucidate the details of what makes foul release the more logical option.

Background: Motivation for an alternative to antifoul:

Initially, foul release coating was being developed simultaneously with biocide containing tributyltin (TBT) self-polishing co-polymer (SPC) antifouling coatings in the early 1970’s. These harmful boat paints worked by polishing the vessel as it moved through the water, killing off any bonding fouling species and was considered to yield very good fouling protection. As a result, the commercial benefits and relatively high efficacy meant that further research into foul release paints did not continue in earnest until the 1990’s.

An early observation of the performance for foul release coatings was its application to an aluminium catamaran on a fast ferry specially designed for high speed use (33 knots). Interestingly, after the implementation of the foul release coating compared to the previously used antifoul coating, the operating crew reported an immediate improvement in performance relating to speed, which increased by a considerable 2-3 knots in all weather conditions. This corresponded to each one hour journey being approximately 5 minutes shorter. Thus, proof that foul release did indeed make this vessel go faster. Additionally, overall fuel consumption was reduced by more than 20,000 litres / month at around a 12% decrease. Subsequently, a study by the university of Newcastle-upon-Tyne was conducted by assessing the drag resistance and surface roughness properties in order to further explain these findings.

Experiments for evaluating drag of foul release systems:

In the research carried out by the university of Newcastle-upon-Tyne, an initial experiment took place using a 2.55-metre-long (9-footlong) plate in the 40-metre-long (132-foot-long), 3.75-metrewide (12-foot-wide), 1.2-metre-deep (4-foot-deep) tank. However this was found to offer up limited speed range. Therefore, a second experiment was undertaken.

The use of a flat plate towing at speeds of up to 8 m/s (26 ft/s) with three different surfaces was deemed more reliable.  The reference surface was a three-coated SPC antifouling system and a three coated foul release system. The towing took place in the 320-metre-long (1,100-foot-long) El Pardo Calm Water Tank (officially known as Canal de Experiencias Hidrodinamicas de El Pardo, or CEHIPAR) using a 6.3-metre-long (21-footlong) plate. The total resistance of the plane was measured with the dedicated dynamometer of the carriage on the tank for the same three surfaces. Essentially, the main findings concluded that the foul release surface exhibits a drag that is on average 1.56% higher than the unpainted aluminium surface, and the SPC surface exhibits a drag that is on average 2.91% higher than the unpainted aluminium surface. In other words, the total drag of the foul release surface was on average 1.41% lower than the SPC surface. The surface coated with a foul release coating had lower drag than the surface coated with the SPC system and would therefore go faster in the water.

Roughness of foul release systems and its contribution to drag:

Most foul release systems in use today are silicone materials based on polydimethylsiloxane (PDMS). PDMS is a non-polar, or uncharged, polymer with an extremely flexible backbone and a low glass transition temperature. In these experiments, the roughness of the different surfaces was measured with a British Maritime Technology (BMT) Hull Roughness Analyser, which is the standard equipment for this purpose in marine technology.

In the flat plane towing tank experiments, it was shown that a foul release surface exhibited lower drag than an SPC surface. What is extraordinary is that the foul release surface exhibited lower drag in the second set of experiments when measurements had shown that its roughness was actually higher than that of the SPC surface because of poor surface preparation.

The Effect of Slime on the Performance of Foul Release Coatings:

It is commonly known that a contributing factor associated with the underlying surface fouling of boats, mainly their underwater hulls, and an additional part to play in drag properties is slime accumulation. This slime build up is a direct result from algae, diatoms, bacteria, and sediment that collect from the seabed. Slime can remain intact even at speeds above 30 knots. Certain SPC antifoulings can reduce slime settlement because their biocides kill the microscopic animal fouling that is part of slime. Such reduction of slime settlement is not possible with foul release coatings because they do not use biocides.

On very rough surfaces, it has been suggested that slime films may actually smoothen the surface and reduce drag. The size of the increase in drag caused by slime (microfouling) is an order of magnitude lower than that caused by weed and barnacles (macrofouling).

Observations about slime fouling on ships coated with foul release systems from slime specific interrogation experiments have drawn some intriguing findings. The thickness of the slime fouling was found to be inversely related to the vessel speed, in turn as speed increases, thickness decreases. Slime build-up is usually thicker below the bilge keel than above it and the slime is readily removed in dry dock or by in-water cleaning.  Even with the slime, the speed and fuel consumption of vessels with foul release systems are similar to what has been observed on vessels with TBT SPC systems.

These findings correlate heavily with the notion that foul release coatings work better and merely need a good cleaning maintenance programme to ensure their continued effectiveness.

Weed fouling is never seen on intact foul release coatings, even after prolonged immersion, and shell (barnacle) fouling occurs only in static situations.

AquaMarine FRC case studies and recent findings:

In light of the findings observed in these previous studies from 2001, independent application of our product has been tried and tested, thus providing a more specific reflection of AquaMarine FRCs. Case studies have been carried out upon differing boat models in various areas of France and across the world as far as New Zealand in our trials.

Impressively, all the feedback from our studies concludes to the key attribute discussed in this article being exemplified: Foul release coatings reduce drag and therefore improve speed when compared to antifoul.

As highlighted in the MBY – 2015 – Sevo article, the Windy 37 boat model garnered impressive results using our biocide-free alternative foul release paint relating to deceased drag and a reduced loss in speed transitioning from the warmer months of the season to mid-October. After these 11 weeks, at 2000rpm the same 11 knots was reported for both times of the year and at 3000rpm a more than acceptable slight drop off of 2.6 knots was experienced. In addition to these maintained speeds throughout the season, not commonly experienced after applying traditional antifoul, the boat operator also reported enhanced handling even late on into the season.

Similarly, another boat (“Heart” Hans Christian 43T) voyaging in France during our European trials also gave an account for the AquaMarine FRCs effect on increasing speed due to its smooth surface producing increased drag resistance. Specifically, the user reported at least one knot increase in average speed as well as better handling during a 10 passage on the sea.



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