Underwater Blade, the Means of Steering a Ship
Puzzle 14 of Alternatives to Plastic Pack
Question is: Underwater Blade, the Means of Steering a Ship
and the answer is: RUDDER
Word Meaning:
RUDDER — (nautical) An underwater vane used to steer a vessel. The rudder is controlled by means of a wheel, tiller or other apparatus (modern vessels can be controlled even with a joystick or an autopilot).
Definitions from Wiktionary.