Single handed development class. Measurements are max values. Most early boats had 2 masts. Sliding seat: The sliding seat was first used sometime during the 1880s. It was subsequently banned and later allowed. Todays limitiation for sliding seat: Horizontal extension from centreline of hull: 2040 mm max. Max. width: 500 mm Max. mass: 12 kg Min. mass: 9 kg The 10 sq meter limitation first established during 1930s? The drawing depicts a version from the mid 1960's.