The King's Privateer by Dewey Lambdin

Fresh from war in the Americas, young navy veteran Alan Lewrie finds London pure pleasure. Then, at Plymouth he boards the trading ship Telesto, to find out why merchantmen are disappearing in the East Indies. Between the pungent shores of Calcutta and teaming Canton, Lewrie-reunited with his scoundrel father-discovers a young French captain, backed by an armada of Mindanaon pirates, on a plundering rampage. While treaties tie the navy's hands, a King's privateer is free to plunge into the fire and blood of a dirty little war on the high South China Sea.