Sorry to hear about the tragic circumstances of this young man.
Have you tried getting a copy of his death certificate? The Genealogist has an excellent Overseas BMD section, which lists the details in the same way as the General Record Office (GRO) Index. His death certificate would show details of his occupation which may well give the name of his ship, from which you could find the shipping line. If you have the name of his ship, it may give more details about him in the ship's log.
I have been able to obtain copies of merchant navy records of various family members - seaman's pockets - which listed the ships they served on and the dates, available from the National Archives (at a cost of course!). You will need his full name and date and place of birth, so you may need to get a copy of his birth certificate first, to make sure you have the correct person.
Apologies if you have already tried this and I am teaching my granny to suck egs. Good luck.