A quick introduction to marine coating
The term “marine coating” defines a class of coatings all intended for use in the marine segment. These coatings include antifouling paints, deck coatings, anti slip paints, bilge paint, boot-topping paints, and protective paints for structures in marine environments. Just as there are different types of marine coating, so there are different requirements depending on the environment, use, and material of your vessel. Which marine coating you need is dependent on a series of factors, including local paint regulations and application methods.
In this article we will provide a guide to the different paints, and what you need to know to select the right one.
From top to bottom paints: marine coatings explained
“Marine coating” covers everything from the top to the bottom of a vessel, as well as structures in marine environments. One paint does not fit all, and given that your vessel can need to deal with not only the Iowa weather but also the conditions of the high seas and far flung locations, it is important to choose the right paint for the job. Marine coatings are applied either while a vessel is in the water (for topside coatings) or dry docked (for bottom paint). Some coatings can be applied underwater, for structures like jetties. For commercial and pleasure craft, there are many who chose to paint their vessels themselves.
This guide will explore the different paints required for different substrates and situations.
Coating above the waterline – Topside paints
Topside coatings are the paints used for the upper hull, interior, and deck areas of a boat, or those areas above the waterline. They protect the boat from sea, sun, sand and the bumps and scratches that will accumulate with time. Essentially, there are 3 types of topside paint: one-part polyurethane, two-part polyurethane, and alkyd enamel. All of these are resistant to moisture and abrasion, can withstand hull expansion and contraction, and resist UV damage while maintaining color and finish.
- One-part polyurethane
A high solids topside paint that is easy to apply and to touch up if damaged. For interior and exterior surfaces.
- Two-part polyurethane
Two-part polyurethanes are superior to one-parts in hardness, gloss and color retention, and UV resistance, but are more expensive and difficult to apply. They are also less flexible than one-part polyurethanes.
- Alkyd enamel
A one-part topside paint that is glossy and easy to apply. They require fewer coats than the two-part polyurethanes and expand and contract with the hull better, particularly good with wooden vessels. These paints require an annual reapplication for maintenance and have the lowest gloss and color retention of the three options.
Coating below the waterline – Bottom paints
“Bottom paint” is coating used to protect a vessel below the waterline. Also known as antifouling paint, its main task is to prevent the build-up of sea life on a boat’s hull. This process (called biofouling) is not just an aesthetic problem; the growth of algae, microorganisms, plants, or animals on a hull also slows the ship’s maximum speed, increases fuel consumption, decreases durability, damages the hull, and can introduce invasive species into foreign waters. Bottom paint prevents this by having a biocidal active ingredient, such as copper, which destroys, deters, or renders harmless these organisms. There are two types of antifouling paint:
- Hard film antifouling
A hard bottom paint leaches a biocide when in contact with water, impeding marine growth without eroding the paint. It is often used for high speed vessels because the hardness of the coating will not wear due to the impact of the water. Once the biocide is leached away the paint will remain, so another coat will be needed to replenish the antifouling layer.
- Eroding antifouling
These coatings wear away through the friction action of being in the water, slowly reducing in thickness and exposing fresh layers of biocide as it does. This reduces maintenance as there is less paint build-up on the hull. There are both single and multi-season options for eroding antifouling.
Legislation regarding biocides and bottom paint is constantly being updated, and it is important to be aware of the latest regulations. We discuss regulations further down in this article.
Protection on the vessel: Deck paint and tank coatings
Painting the boat will give it the best possible, longest lasting protection against the elements. High-quality, water-based deck and tank latex paints are more flexible than oil-based paints; they are also suitable for wood because they can withstand the wood’s moisture fluctuations better than other coatings.
- Deck paint
Boat decks and structures in marine environments are hazardously slippery when wet. To protect passengers and employees from accidents, a vessel needs adequate anti slip protection. Deck paint not only needs to provide anti slip protection, it needs to withstand all the elements and all the wear and tear that comes with traffic.
- Tank coatings
Whether lining cargo tanks, potable water tanks or wastewater tanks, the right coating can save you from costly damage. Most commonly tank linings are epoxy, polyurethane, or polyurea, depending on the cargo of the tank. The lining needs to withstand and not contaminate the cargo, while also allowing for fast transfer times with cargo changes.
Companies that sell cargo coatings, such as AkzoNobel, PPG, and Hempel, also provide helpful Cargo Protection/Resistance Guides, to check the suitability of the coating against your cargoes.
Marine coating manufacturers in the US – Hempel, PPG, AkzoNobel, Sherwin-Williams
The marine coatings market is vast, and cargo vessels currently make up the largest share. The manufacturers that dominate the market include Hempel, PPG, AkzoNobel, and Sherwin-Williams. These big players sell everything from yacht paint to antifouling coatings for cruise liners and cargo ships.
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The US marine coating regulations
The chemicals used in marine coatings can affect the delicate ecosystems of the marine environment. Tributyltin (TBT) was used as a biocide until it was discovered that it was highly toxic to creatures all the way up the food chain, an example which the marine coatings industry does not want to repeat. The effects of copper as a biocide are currently under scrutiny, with stricter environmental regulations being introduced across the globe. On the other hand, biofouling leads to the introduction of non-native and invasive species to an ecosystem and also needs to be strictly controlled. The legislation which particularly relates to the US has been relatively stable for the past 10-15 years.
The primary piece of legislation is still the NESHAP (National Emission Standards for Hazardous Air Pollutants) for Shipbuilding and Ship Repair, which is a categories and limits-type piece of legislation – different types of paint have different VOC limits. Several counties in California also have Marine-specific VOC legislation, which is slightly stricter than that of the whole of the USA. In addition, SCAQMD (California South Coast Air Quality Management District) is proposing to merge Marine and Pleasure Craft legislation.
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