barko

What it actually is. Bigger than a rowing boato, smaller and humbler than a ŝipo: the Reta Vortaro defines a barko as a vessel fit to carry goods and a few people on a river or along a coast. Think barge, lighter, working boat. It is an old word for an old kind of craft, made of reed or timber, with the ends lifted clear of the water, and it belongs to calm water rather than open sea.

The English seam that is not there. English bark is two words wearing one spelling: the boat, and the stuff on the outside of a tree. Esperanto splits them and never lets them touch. The boat is barko. The bark of a tree is ŝelo, which also does peel, rind, shell and hull - one Esperanto word for the outer layer of anything. This is the same shape of mismatch as tosto and rosti, where English collapsed two histories into one sound and Esperanto simply did not. When two English senses share a spelling, assume Esperanto has two roots until you have checked.

The nearby water words. Velo is a sail, remilo an oar, bordo the shore, and ŝipeto is the ordinary diminutive if you simply want a little boat and do not need the historical kind.