As any sailor will tell you, any patch of ocean has its own distinct flavor, in the way it moves, the way it smells, the weather found there, and of course in the things living there. In short, each patch of ocean has its own Way.
Arth is a world made up of semi-continuous biomes, each with its own ecology and path. The oceans of Arth are no exception. Each ocean biome has its own way. Most Ocean biomes are huge in comparison to their land cousins; yet the Ocean has an uncounted number of biomes of all sizes. The Ocean of the Known World is fractured, just like ThirdLand. Now in most cases, the change in ocean biome does not touch a sailor, byt some do.
This can make sailing problematic. Longdistance sailing is only possible on Arth with Coursefinders (oceanic Pathfinders). They not only know the biomes of the ocean, they have a "Feel" for them that allows them to sense shifts in travel paths and changes in way. Humans are the only species that are known to have the pathfinding knack, and even then it is in a small percentage. Most people in Arth, stay home. It is both safer and more comfortable being in a familiar "way".
The sea clans have the knack in a disproportionate numbers. Since the knack is required to travel their "home" with great safety, it seems to be a fairly common gift for these people.
The Andoran Ocean is bordered by NorthLand in the North and ThirdLand in the East. There is no firm border for it South and East, except the areas west of SecondLand and south of FourthLand are mostly underexplored. The east side of Thirdland has little in the way of civilization or good ports (as most of the east side are high cliffs populated by winged folk). The Imperium has commisioned a number of ships to explore the sea, to find more Lands and islands. The Emperor has also toyed with offering a reward, like he gave those who discovered MaskLand, as a regular bounty for finding new Lands.