bow or prow of boat
舮 centers on the front end of a boat: the bow or prow, the part that cuts through the water.
舮 combines 舟 (boat) with 户 (door), likely suggesting the front opening or entry of a boat, i.e., the bow. The exact historical development is uncertain.
The left side 舟 is a boat, and the right side 户 looks like a door. Picture the bow of a boat as the 'door' at the front that opens onto the water.
For ロ, imagine a row of boats lined up, and you point to the bow of the first one: 'Row' -> ロ, the front of the boat.