Regulation 18 (4) A vessel engaged in trawling shall exhibit(a) two all-round lights in a vertical line, the upper being green and the lower white, or a shape consisting of two cones with their apices together in a vertical line one above the other; a vessel of less than 20 metres in length may instead of this shape exhibit a basket;(b) a masthead light abaft of and higher than the all-round green light; a vessel of less than 50 metres in length is not obliged to exhibit this light but may do so; and(c) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a stern light.