Coracles have different designs, as they are designed for the river conditions where they are built and used. The Teifi coracle is flat-bottomed, because it is designed for use in the shallow rapids which common on the river in the summer. The Carmarthen coracle is rounder and deeper, because it is used in tidal waters on the Tywi, where there are no rapids. Teifi coracles are made from local wood. They use willow for the body of the boat, called a lats. Hazel is used for the bit around the top, called Y bleth in Welsh. Tywi coracles have been made from sawn ash for a long time. These days working boats are made from fibreglass. Teifi coracles do not use nails. The twisting together of the lats makes them strong. The Carmarthen coracles use copper nails and are not twisted together.