Section 3 in The Merchant Shipping (Prevention of Collisions at Sea) Regulations, 1975
3. Horizontal positioning and spacing of lights.
(a)When two masthead lights are prescribed for a power-driven vessel the horizontal distance between them shall not be less than one half of the length of the vessel but need not be more than 10 metres. The forward light shall be placed not more than one quarter of the length of the vessel from the stem.(b)On a vessel of 20 metres or more in length the side-lights shall not be placed in front of the forward masthead lights. They shall be placed at or near the side of the vessel.
