Plastiki, the boat made from 12,500 plastic bottles, will leave New Caledonia this week for the final leg of its journey to Sydney.

The 60-foot catamaran has sailed nearly 7,000 miles since leaving San Francisco 108 days ago to raise awareness of the Great Pacific Garbage Patch, the vast, floating, rubbish patch in the world's largest ocean.

Inspired by the 1947 trans-Pacific Kon-Tiki expedition from South America to Polynesia by Norwegian explorer Thor Heyerdahl on a raft made from carved-out balsa husks, British adventurer, ecologist and banking heir David de Rothschild, 31, concocted the idea after reading a UN report on ocean ecosystems.

Plastiki, in which the bottles provide 68 per cent of the buoyancy, has already stopped in the Line Islands and Western Samoa.

The voyage, which aims to highlight the dangers of plastic pollution, over-fishing and climate change to the world's oceans, is expected to start its last and most challenging leg tomorrow after arriving in Noumea, New Caledonia, last week.