Is this normal for this AI to place so many buoys?
Yes, boys are placed every 25 tiles. This is made to avoid ships getting lost and to improve the pathfinder performance ( see: viewtopic.php?t=75339
And another thing, have a look at this screenshot: http://imgur.com/W7hbh5q
. This yellow line is the route ship takes. It's really unefficient.
The 2 pathfinders used by the AI (straight line, coast) were chosen because of their speed. The price for that, in case of the coast pathfinder, is that it sometimes gives sub-optimal routes.