For laypeople and casual sailors, thinking of the rudder as just redirecting water is good enough.
But water and air are both fluids and the same aerodynamic/hydrodynamic rules apply.
A rudder on a boat or airplane is symmetrical in cross section; the chord on both sides is equal. Wings and hydrofoils are asymmetrical; usually the “top” has a deeper chord than the “bottom”. But rudders are a still a kind of wing in that they generate a useful force by redirecting a fluid and thereby inducing a pressure differential. The pressure differential between the two sides is what causes lift - vertically with wings/foils and horizontally with rudders. If you think about it, this makes perfect sense – it would be silly to think that rudders and ailerons and elevators obey different laws than wings. In fact, one of the first things you learn as a racing sailor is that the sails themselves are wings - they’re not “parachutes” as commonly believed.
Anyway, my point was that you can stall a rudder just like an airplane can stall its wings- if the angle of attack is too high.
Stalling, the rudder, most commonly occurs during a round up, if you’re familiar with sailing with spinnakers. The rudder in that case is no longer able to generate enough lift (turning force) To counter the turning force, imparted by the force on the spinnaker forward of the center of mass of the boat, and the boat turns uncontrollably.
I am just speculating, but if the rudder became very misaligned compared to the direction of the ship, then when power was restored, the rudder might not be able to establish laminar flow and therefore would be stalled and unable to provide turning force.
But water and air are both fluids and the same aerodynamic/hydrodynamic rules apply.
A rudder on a boat or airplane is symmetrical in cross section; the chord on both sides is equal. Wings and hydrofoils are asymmetrical; usually the “top” has a deeper chord than the “bottom”. But rudders are a still a kind of wing in that they generate a useful force by redirecting a fluid and thereby inducing a pressure differential. The pressure differential between the two sides is what causes lift - vertically with wings/foils and horizontally with rudders. If you think about it, this makes perfect sense – it would be silly to think that rudders and ailerons and elevators obey different laws than wings. In fact, one of the first things you learn as a racing sailor is that the sails themselves are wings - they’re not “parachutes” as commonly believed.
Anyway, my point was that you can stall a rudder just like an airplane can stall its wings- if the angle of attack is too high.
Stalling, the rudder, most commonly occurs during a round up, if you’re familiar with sailing with spinnakers. The rudder in that case is no longer able to generate enough lift (turning force) To counter the turning force, imparted by the force on the spinnaker forward of the center of mass of the boat, and the boat turns uncontrollably.
I am just speculating, but if the rudder became very misaligned compared to the direction of the ship, then when power was restored, the rudder might not be able to establish laminar flow and therefore would be stalled and unable to provide turning force.