A flat bottomed boat is a bot built without a "V" shaped keel. This means the boat has to be quite wide (to achieve the same buoyancy) and while the lack of the keel means the ban be blown sideways across the water by the wind, the boat has the advantage that it can be used in very shallow water.
I'm guessing it's a boat with a flat bottom.
PuntBargeTrowJon Boat
A Flat Boat is a boat with a flat bottom used for transporting heavy loads on inlend waters.
Peerow
Froe
...is called a skiff.
punt
Any sort of goods. The flat bottom allows the boat to navigate in shallow water.
· dinghy
fluitschips
lower
A Landing ship, an LCVP, an LCT, a Higgins Boat or an LCI.
Displacement Sailboat