Seaman's Handbook

ANNEX I. Positioning and technical details of lights and shapes

(a) The masthead light of high speed craft may be placed at a height related to the breadth of the craft lower than prescribed in paragraph 2(a) (i) of this annex, provided that the base angle of the isosceles triangles formed by the sidelights and masthead light, when seen in end elevation, is not less than 27.(b) On high sped craft of 50m or more in length, the vertical separation between foremast and minmast of 4.5m required in paragraph 2(a)(ii) of this annex may be modified provided that such distance shall not be less than the value determined by the following formula: y = (a + 17T)C + 2 1000 where: y is the height of the mainmast light above the foremast light in metres; a is the height of the foremast light above the water surface in service condition in metres. T is the trim in service condition in degrees. C is the horizontal separation of the masthead lights in metres.