A number of 6 m Trailer Sailers sailed on Lake Eyre in 1975 , 1976 and 1984 when the flood depth reached 3 â `` 6 m. A number of 6 m Trailer Sailers sailed on Lake Eyre in 1975 , 1976 and 1984 when the flood depth reached 3 â `` 6 m ( 10 â `` 20 ft ) .