What happens to the propeller when the shear pin breaks?

When the shear pin breaks, the propeller is designed to disconnect from the drive system, which prevents further damage to the engine and the propeller itself. This means that the propeller cannot turn until the shear pin is replaced. This safety feature helps protect the boat's propulsion system by allowing the propeller to disengage without causing significant harm to itself or other components of the powertrain.

The other situations indicated would not accurately describe the performance of the propeller upon a shear pin failure. For instance, if the propeller were to become stuck, it would indicate a different kind of mechanical failure not related to the shear pin. If it spun freely, that would imply a loss of control and could allow for potentially dangerous conditions. A broken propeller or one that remains attached yet non-functional would also indicate a failure of the intended safety mechanism that the shear pin provides.