gunwale
舷 refers to the upper edge of a boat's side, the gunwale. It is a specific nautical term for that structural rim.
舷 combines 舟 (boat) and 玄, which likely contributes the sound. The character was created to specifically denote the gunwale of a boat.
The left side is a boat 舟, and the right side 玄 looks like a mysterious dark line along the top edge. Imagine the gunwale as that dark rim running along the boat's side.
For ゲン, picture a general standing on the gunwale of a ship, giving orders: general -> ゲン, and he's right on the edge.
starboard
port (left side of vessel)
side of a boat; gunwale
ship's side; broadside
both sides of a ship
freeboard
half watch ashore; port and starboard liberty; shore leave for half of a ship's crew at once
coming alongside (a boat, pier, etc.)
broadside (firing of all the guns on one side of a warship)
ceremonial assembling of a ship's crew on deck
broadside gun; broadside cannon
gangway (ladder)
running lights; sidelight; side light
porthole
gangway
gunwale
fender (on a boat); bumper (on a dock, pier, etc.)
fender (on a boat); bumper (on a dock, pier, etc.)