He and his father Bob went to the USA to compete in the Nacra 5.2 North American Championships in 1982, where they placed fourth.

John then traveled to Monterey Bay with fellow Australian David Renouf where they finished in 4th place in the Nacra 5.8 North American Championship.

In 1985 Forbes won Australian Combined High Schools Championship outright with his brother Rod on a Nacra 5.2.

Rod Waterhouse's inability to travel overseas in 1989 led John to join up with rival Mitch Booth, and together they won the 1989 World Championship (Houston, Texas) 36 points ahead of Giorgio Zuccoli from Italy.

As a result, they were jointly awarded the prestigious 'New South Wales Yachtsman of the Year' trophy in November 1991 and again in 1992.

As a final toast, they were again jointly honored with the distinguished award of Ampol Australian Yachtsman of the Year in 1992.

They then went on to win the World Championship by 18 points over long-time training partners Roland Gaebler and Rene Schwall (Germany).

By the end of the year they had finished a four-month European campaign and captured the Number 1 spot on the 'ISAF O’Neill' World Rankings after winning the 'Princess Sofia Trophy' (Spain), the European Championship (Spain), 'Kiel Week' (Germany) and placing 3rd in 'Hyères' and 4th at the World Championships in Copenhagen, Denmark.

By the end of January 2000 they were selected into the Olympic Team to represent Australia in their hometown of Sydney, where they won the silver medal.

On 11 December 2001 Forbes and Bundock were one of five finalists for the NSW Institute of Sports “Athlete of the Year”.

As a result of the successes both in 2002 and 2003 Forbes and Bundock also received the following accolades: Australian Institute of Sport – Team of the Year.