Hi there,
I believe your best option is to expect to find him as RN and thus I urge you to follow up with the UK National Archives. Perhaps he served on more than one RN vessel, perhaps at different times he was stationed on different stations throughout the Empire, but his PAY would be authorised via the British Admiralty with offices on Whitehall, London, and I would hope their archive records would be at Kew, Surrey, England.
Cheers, JM