The technology and chemistry of painting a ship
Our member Ian Royston, who was Chief Chemist at International Paint in the late 1990s, gave us a fascinating talk entitled "For a Ha'porth of Tar," in which he illustrated the process and chemistry of painting a ship — and showed how much has changed since he first gave this talk, as a technical paper, to the Oil & Colour Chemists' Association in 1998.
Ian began with an uncomfortable truth: we build ships from steel, one of the most corrosion-prone materials available, then put them in seawater for decades. Protecting them starts before the first plate is even cut, with a thin zinc-rich primer that survives the welding torch and continues through tough epoxy coatings chosen for their resistance to knocks, chemicals and the alkaline conditions created by the ship's own corrosion protection.
He also described how shipbuilding itself has changed, with ships now built in large, prefabricated blocks, assembled and painted as far as possible in covered, heated sheds, in place of the open slipways once universal in the trade. Japan led this shift from the 1960s, well ahead of most of the rest of the world.
He traced the shift from coatings a ship's own crew could slap on with a brush between ports to today's professionally sprayed, two-pack systems, and touched on some lesser-known oddities of ship painting: why aluminium superstructures on cruise ships quietly corrode without the tell-tale rust streak steel gives off, and why most cruise ships are painted white — not just for a clean, nautical look, but because a white ship reflects heat and takes some of the load off the air conditioning.
The most striking part of the talk concerned the control of fouling: the barnacles and weed that roughen a hull and burn extra fuel. Ian described how tributyltin, once the most effective antifouling chemical ever devised, was found to be causing severe harm to marine life at almost unimaginably low concentrations and traced the regulatory story from the first restrictions in France in 1982 to a worldwide ban in 2008. Its replacements, he explained, range from the familiar (copper) to the exotic, including one compound that doesn't kill barnacle larvae at all, but simply won't let them settle.
He closed with a reminder that the chemistry may have moved on, but the central engineering problems Noah faced — keeping water out of a wooden, then steel, hull and how to stop things growing on it — have never gone away, and that today's regulators are still wrestling with the environmental trade-offs of every solution devised so far.
Questions from the floor ranged from the conformance to environment rules by some rogue states to just how long a ship is designed to last, which Ian fielded with his customary thoroughness.
Our next meeting is at the Witham on Monday 9 November at 10:00.
Report by Ian Royston