The waves were very big and were coming up and over the transom and mainsheet traveller and were hitting the rudder blade while lifted.
From the independent.co.uk
The gyrocopters came as plain or fancy as the owners could afford, but all were equipped with a pusher engine, one rudder, one rotor blade, and a single seat with steering stick.
From the time.com
A report by the Signal Corps Aeronautical Board said the propeller blade looked like it struck a wire supporting the rudder.
From the lohud.com
However, the sweep oars are used for both ruddering and sweeping wherein the blade can come out of the water for an out of water recovery unlike a rudder to which a tiller control arm is secured.