Eh, ships sailing in a straight doesn't make sense, no matter what, especially as you can't see any enemy ships and I assume that "Battle lines" would only be used in battle / close to battle. Also yeah, they look like jet boats what with their massive trails. You probably wouldn't see much other than massive ridges in the water just behind them and near them. But very probably not bubbles.
About the land, IMO, the fences look sort of strange as the mountain looks like one flat shape instead of being kinda curved so that you have paths where fences go as you go up the mountain. Because of that, they also look as if the spots are just random spots amongst the mountain with no real connection to the others. The trees in the middle stick out a bit too much I reckon, I'd tint the bright green down. Upper part looks good.. other than fucking floating fences...? If there was a path, sure, but like that, no way :/ A lot of the buildings look like randomly placed ones in a line (especially up top) but it's just a minor detail. Overall, it's a great terrain with a lot of flaws IMO - the clouds are bright only on the bottom, they would be all over the place (up top).
Also, it's sailors, not sailers. T_T