Like jellyfish stings, sand rash and sea storms, rusting is a pest that just won't go away, as the hull and outer body of ships are worn down by perpetual contact with saltwater. Due to maintenance costs, NACE International estimates that the total cost of marine corrosion worldwide is $50-80 billion every year.
This is a major issue for cruise companies as rusting can degrade the durability of ships built to last for 30-40 years. If they fail to mitigate the risk of corrosion, operators can find themselves sidelining key vessels in dry docks for 10-15 days, as engineers work round the clock to patch up ugly, potentially dangerous damage to hull surfaces, so bringing that number down by just one day can create substantial revenue.
"A cruise ship is a service vessel, so if a ship is in a dry dock, then the cruise company is not making any money from that vessel," says Martin van Leeuwen, manager at the International Zinc Association (IZA).
"I've seen a report that mentions that indirect corrosion downtime costs for cruise ships can go up to $1 million per ship per annum, which can be five times more than the direct corrosion maintenance and repair costs. These indirect costs are caused by lost revenue."
There's also a psychological element here, as passengers associate corroded ships with rusty relics and fatal accidents at sea.
To combat the threat posed by rust, duplex protective coatings can be added to a cruise ships' exterior, creating two overlapping layers that provide a barrier for the underlying steel. Unlike organic paint systems, this thermal spraying technique creates a layered metallic zinc coating that is highly durable and extremely long-lasting, forming an ideal substrate for topcoats.
"With thermal spraying, you melt the zinc down to tiny droplets that are then propelled or sprayed on the surface of steel, where they solidify instantly and form a very dense metallic layer on top of the steel," Van Leeuwen explains.
"It's then possible to apply additional layers on top of the initial zinc layer so you can have additional protection."
For Van Leeuwen, this combination of resistance to corrosive elements and durability is perfectly exemplified by offshore wind towers that are able to stay in service for lengthy periods in harsh environments without coating maintenance.
"All the offshore wind farms installed in places such as the North Sea have a protective, firmly sprayed zinc layer on the outside of the steel," he says. "Many of them are now 25 years old or more and are still in operation because of these coating systems."
Customers need not only look to wind towers for proof of success; numerous maritime organisations are now using zinc coating to safeguard their ships.
The IZA even offers a long-term trial for ship owners to try the coating method themselves. "There's no better way to convince a customer of the quality of the system than by allowing them to test it out," Van Leeuwen says. "Testing periods are fairly long because a ship normally only goes to dry dock every five years, and within that time it should be possible to get a good idea of the performance of the system compared with the ordinary painting processes."
The end result is a more durable, sustainable protection system that reduces maintenance expenditures and is more environmentally friendly than standard painting methods. As the IZA continues to promote awareness of zinc coating methods and the technology behind this process becomes more sophisticated, it seems increasingly likely that more cruising companies will wake up to the benefits of using duplex coatings to safeguard ships from corrosion. After all, creating more durable vessels is a sure-fire way of saving costs in the long run.