Speed will be of the essence as salvage crews attempt to stop fuel leaking from the sunken New Zealand naval ship off the coast of Samoa.

The HMNZS Manawanui ran aground last weekend on a reef about one nautical mile off the south coast of Upolu, Samoa’s most populated island. The specialist dive and hydrographic vessel was on its third deployment, conducting a reef survey, when it caught fire and sank.

The ship has come to rest at a depth of up to 150 metres, which means it may be relatively undisturbed even during storms. Any hull cracks from the impact should not be exacerbated.

But depth makes the salvage operation challenging. Crew may need decompression chambers, and there’s only a narrow window of time to seal any fuel leaks – and, ideally, pipe out more than 900 tonnes of marine diesel the ship carries.

The Manawanui’s sinking is a marine disaster. But it arguably poses a lesser risk than the oil spill caused by the container ship MV Rena, which ran aground near the Astrolabe Reef off Tauranga in 2011.

The Rena was loaded with 1,368 containers, some of which contained hazardous materials, as well as 1,700 tonnes of heavy fuel oil. It also carried thousands of tonnes of dairy products, which effectively........

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