user: Question: What is the number of the sail with an overall length of 13.68?
Columns: ['Position', 'Sail number', 'Yacht', 'State/country', 'Yacht type', 'LOA (Metres)', 'Skipper', 'Corrected time d:hh:mm:ss']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'GRE55', 'Aera', 'UK', 'Ker 55', '16.57', 'Jez Fanstone', '4:02:52:09']
SQL:

assistant: SELECT "Sail number" FROM "Table" WHERE "LOA (Metres)" = '13.68';