RCM Payable on Ocean Freight???

Yes You have to Do RCM by depositing under CGST/SGST

As per Notification 10 IGST ( R), under S.no.10
Services supplied by a person
located in non- taxable territory by
way of transportation of goods by a
vessel from a place outside India up
to the customs station of clearance
in India is under RCM

As per Section 13 (9) , IGST Act
9] The place of supply of services of transportation of goods, other than by way of mail or courier, shall be the place of destination of such goods.so you have to deposit the RCM done  under CGST/SGST