The world’s best sailors will be vying for Olympic berths in the ISAF Sailing World Championships from December 3 to 18.

Three-quarters of the spots at the 2012 London Olympics will be decided in the testing waters off Perth and in Fremantle Harbour, with more than 1,200 sailors from around 80 countries competing.

It is only the third time the World Championships have been held – with previous editions in Spain in 2003 and Portugal in 2007 – and will be the biggest sailing event in Perth since Australia’s doomed 1987 defence of the America’s Cup.

All of the 10 Olympic sailing classes are taking part in the regatta, with all sailors eyeing the 380 spots available for London.

The famed local “Fremantle Doctor” wind usually springs up in the afternoons and is sure to test the skills of the competitors, especially those unaccustomed to its vagaries.

It should provide some spectacularly fast racing, with the events featuring small dinghies, windsurfers and just one keeled boat.

As expected, there will be a strong local flavour to the event, with Nathan Outteridge and Iain Jensen ranked second in the world in the spectacular 49er class, and Mathew Belcher and Malcolm Page top-ranked in the 470 class.

Reigning world champion and 2010 ISAF Sailor of the Year Tom Slingsby will be the man to beat in the Laser class.

But there will be plenty of overseas competition, led by Britain’s Ben Ainslie, who competes in the heavyweight Finn class.

Ainslie has won three Olympic gold medals and is ranked as one of the greatest Olympic sailors.

The Star class, which bows out of the Olympics after London, features the only keeled boats in the event, and Brazilian pair Robert Scheidt and Bruno Prada, silver medallists at Beijing in 2008, will be favoured after winning the Olympic test event in August.

The ISAF Sailing World Championships launch tomorrow, including women’s match racing, which makes its Olympic debut in London.