If you have a look at the map in the first post of this thread, the story will be taking place in the forest between Sices and Bouche. There are rivers and lakes running through the region that would eventually connect to the coast both to the North (the Montaigne / Avalon Straight) and Dore Bay in the South. I imagine they should certainly be navigable for a ship your size, with a bit of care in some places probably.