By Water 3: Journeys from and to

The crew of the "Syarduyar Arhilka" depart from the island of the Turven, leaving one member behind. After a long journey across desolate seas, they come upon a ruined city which appears to have been where giant serpents ruled over men, as slaves.
Travelling north after many weeks, they eventually reach Saldankandul, in Kardakan. Fadshi-qar Wafar wishes to raise an army to attack the giant serpents - or "Qosidar" - on their island to prevent an attack by them. Unconvinced, Rakvir Stagarnik departs. Wafar convinces Saldjaran Manzir and Zgar Zavzar to conduct a campaign, but imperils his marriage to Rakvir's daughter Ashmara, who finds her father after a lonely journey through the Palqahcat mountains. While a great expedition journeys south for the "island of the Qosidar", Rakvir sets off east across the ocean on his own to prove his theory that the world is round.
The third volume in the epic "By Water" is set in a distant planet, not too dissimilar from our own, written by Richard Hernaman Allen.