Scheidt and Prada took a commanding 18-point lead into Saturday's top-10 medal race and finished fifth to cement first place ahead of Robert Stanjek and Frithjof Kleen of Germany, who leapfrogged Americans Mark Mendelblatt and Brian Fatih to finish second.

The Brazilian pair sailed consistently throughout the championships including a win, four second and two third placings over the course of 10 races leading up to Saturday's medal race.

They sailed a sound race in light and shifting wind conditions on Saturday to clinch back-to-back world titles, ending a year in which they won six international Star events, including the Weymouth and Portland International Regatta in July.

"To be Star world champion I think is the biggest achievement that a sailor can have," Scheidt said. "To win two times is to be a part of the story of Star class, it means a lot. The Star class is very special. It's the class of all the biggest names.

"This year we have improved a lot in our sailing and our main goal was always to do well here in Perth, so coming through this year and managing to peak at this moment is very special.

"It means that we are on the right track for the 2012 Olympics." The Star has been an Olympic class since its debut at Los Angeles in 1932 but will be contested for the last time in London next year.

Australia's top-ranked pair of Nathan Outteridge and Iain Jensen will take a comfortable 17-point lead into Sunday's top-10 medal race in the 49er skiff class.

Outteridge and Jensen had fifth, seventh and 10th placings in Saturday's races to take their overall points tally to 85, ahead of Emil and Simon Toft Nielsen of Denmark with 102 points.

"It's a good feeling," Outteridge said. "We've been toughing it out all week and it's been really close on points and now we've got a 17-point lead so hopefully tomorrow we can just avoid coming last and that will be enough to win it for us." World No. 2 Nico Delle Karth and Nikolaus Resch of Austria had two wins and an eighth placing Saturday, continuing a stunning comeback from 22nd place to qualify in seventh place for the medal race.

"It was a great day for us," Resch said. "It started already yesterday with the first sea breeze race which we won, and we had a good feeling in today's racing too." World No. 1 Tom Slingsby of Australia came close to wrapping up his fourth world title in the laser class Saturday and needs only a mid-fleet finish in Sunday's top-10 race to clinch the gold medal.

The 27-year-old takes a 14-point lead over Germany's Simon Goteluschen into the medal race after finishing 10th and 12th in Saturday's races.

Slingsby had previously won five of the 10 races in the class and said he was disappointed not to clinch the gold medal on Saturday.

"I've been in this position plenty of times before," Slingsby said. "I've got more experience in this position than anyone in the fleet.

"My competitors I think will be more nervous than me ... and I'm ready to go."