Section 15(2)(ii) in The Merchant Shipping (Standards of Training, Certification and Watchkeeping for Seafarers) Rules, 1998
(ii)have approved sea-going service as an officer in charge of a navigational watch on ships of 500 gross tonnage or more for a period of not less than three years. However, this period may be reduced by the Chief Examiner concerned to a period of not less than thirty months, or pro-rata, if not less than one year of such sea-going service served as Chief Mate;