* Winds below six knots
* Races crucial for Japan and France teams (Updates with postponement of racing to Thursday)
May 31 (Reuters) - America's Cup racing was delayed until Thursday after the wind in Bermuda's Great Sound dropped below the average speed needed for the high-tech catamarans to race on Wednesday.
The first race of the day, a critical battle between the crews at the bottom of the table, SoftBank Team Japan and Groupama Team France, was earlier postponed by the umpire as wind speeds dropped below six knots (11 kilometres per hour).
After the crews and their support boats had sat out on the race course waiting for wind for several hours, the decision was eventually taken to abandon racing for the day.
"ACRM (America's Cup Racing Management) have now confirmed that unfortunately wind is too light to allow for racing today," the organisers of the event, the oldest trophy in international sport, said on Twitter.
"Good news is that we have a spare race day on the schedule tomorrow for exactly this reason, and Races 4-7 will now shift to Thurs 1st June," they added.
The opening day of the America's Cup had been postponed last week due to near gale force winds blowing in Bermuda, making it too dangerous for the crews to compete in their state-of-the art catamarans, whose "wing" sails soar 25 metres above the boats.
French skipper Franck Cammas said in a televised interview before racing was due to begin at just after 1700 GMT that the conditions would be tricky, with light and shifty winds.
Groupama Team France, the pre-event underdogs, have struggled to get their 50-foot foiling catamaran to "fly" as well as the other five crews in the regatta.
But the French, who were comprehensively beaten by America's Cup holders Oracle (NYSE:ORCL) Team USA on Tuesday, have won two races, including a victory over Britain's Land Rover BAR.
"We have to create the speed to fly, this is the challenge for us," Cammas said.
SoftBank Team Japan are also on two points going into their encounter with the French crew, who had been scheduled to race Ainslie's team later in the day.
Each of the six teams races the other twice in the head-to-head match race format, with a point for the winner. The challenger with the fewest points at the end of the qualifiers will not go through to a semi-final round.