Monday, 5 December 2011

Clean bottom

The Antipodean Mariner was trying to think of a witty, double-entendre for this posting but this was the best he could come up with.

Ships during their trading life have statutory periods during which they have to dry-dock for inspection and painting of the underwater hull. A dry-docking and paint job costs about $500,000 every five years for a newish ship not including time off-hire in the dock. Evironmental regulations have banned anti-fouling coatings that release heavy metals (tin and lead) into the marine environment. Towards the end of the normal, five year docking cycle speed slows and fuel consumption increases as barnacles and slime get established on the hull. The amount of growth experienced depends where the ship is operating the and how ‘friendly’ the environment is to the crustaceans.

One of the Antipodean Mariner’s ships was experiencing a dramatic increase in fuel consumption and speed loss after trading for an extended period in the tropics. A cargo was secured for a voyage into the cooler waters of the North Pacific and a bottom clean scheduled for the voyage home.

The technique used is to anchor the ship in clear water and clean the marine growth off with rotary scrubbing brushes. A team of divers can do the whole underwater hull and propeller in a couple of days for a fraction of the cost of dry-docking.

The photos show the divers cleaning around the ship’s stern, with the economy flow-fin in the foreground and propeller visible in the background.

Before and after the hull cleaning.



Job done and she’s on her way to load her next cargo. Speed has increased by two knots and fuel consumption reduced by six tonnes a day.

The Antipodean Mariner


  1. What vessel are you working on in those pictures?

  2. The underwater shots are the hull of 'RTM Wakmatha', 90,000 DWT, courtesy of the diving report. She has since been dry-docked.