Just wanted to share two resources that I've found very helpful while thinking about sailing in Greyhawk:
Designing a Ship for a Fantasy Novel
I tend to favor the 14th century and earlier when looking for inspiration for D&D, but I made an exception when looking at ships. My primary reason is that 15th century ships make better adventure locales than their smaller predecessors.
I felt this was justified since overland travel is so dangerous in Greyhawk and teleport so hard to come by, great ships might have been developed "earlier" than they were in our world.