Weather buoys range in diameter from 1.5–12 metres (5–40 ft). Those that are placed in shallow waters are smaller in size and moored using only chains, while those in deeper waters use a combination of chains, nylon, and buoyant polypropylene.[14] Since they do not have direct navigational significance, moored weather buoys are classed as special marks under the IALA scheme, are coloured yellow, and display a yellow flashing light at night.