A fundamental design problem of the Kiwiprop propeller has been the optimal exploitation of the known properties of the Zytel composite material so as to allow the sacrifice of one or more blades when the moving propeller comes into sudden contact with a solid object.
We remain firmly convinced that it is far better to sacrifice one or more blades whose unit price is about 100 € rather than damaging an entire transmission whose cost or replacement can, depending on the extent of the damage, reach several thousand euros.
The bottom line is that something has to break when a rotating propeller encounters a massive large object such as a floating tree trunk.
The photo below was taken in the Galapagos after a second encounter at cruising speed, with a submerged tree trunk, during a cruise between the Mediterranean and Australia. The presence on board of sets of spare blades made it possible each time to replace the damaged blade, while diving, in a few minutes which allowed to continue the journey without further damage and with the unwavering conviction of the usefulness of the sacrificial blade concept.
The ability to run the engine was seriously questioned in this situation.