Note if the vessel is <20m, the sidelights can be in front of the forward masthead, otherwise they must be aft of it (Annex I).

Rule 30(a)
A power-driven vessel underway shall exhibit:
(i) a masthead light forward;

(ii) a second masthead light abaft of and higher than the forward one; except that a vessel of less than 50 meters in length shall not be obliged to exhibit such light but may do so;

(iii) sidelights; and

(iv) a sternlight.