Definition
Small, hinged steering surfaces attached to the rear of a seaplane's or floatplane's floats (or to the hull of a flying boat) that extend down into the water to provide directional control while taxiing on the surface. They are linked to the rudder pedals and are raised clear of the water before takeoff and after landing.
Plain English
Little fins on the back of a seaplane's floats that drop into the water and let the pilot steer while moving on the surface. They are pulled up out of the water before takeoff.
Context Anchor
Seen in seaplane operations, especially during water taxi, docking, and pre-takeoff checks.
Derivation
The name is descriptive: 'rudders' that work in water rather than air. The aircraft's main rudder steers in the air; water rudders do the equivalent job on the surface, where the airflow over the tail isn't strong enough to make the air rudder effective at low speed.
Why Pilots Care
They give positive directional control on water, reducing the risk of drifting into obstacles or losing heading in wind or current.
Analogy
Think of them like small boat rudders attached to the back of the floats. When they are down, they help the seaplane steer on the water; when they are up, they are out of the way.
Intuition Check
Water rudders are not the airplane’s tail rudder getting wet. They are separate small steering surfaces used only for control while the seaplane is on the water.
Example Sentence 1
Before adding power for takeoff, the pilot retracted the water rudders so they wouldn't be damaged on the step.
Example Sentence 2
With the water rudders deployed, the seaplane maintained a steady heading despite the crosswind.