Long Fiber CompositesInitially, the concept of simply sliding a new blade in to replace a damaged one was well received, according to Stahl, but using composites instead of metal met with some resistance. "'There is no way a piece of plastic can push my boat through the water' was common feedback," said Stahl.
With long fiber composites being an integral element to making his interchangeable blade design practical and cost effective, Stahl pressed on. "The first 5-to-10 years it was an up-hill battle to prove a composite prop was as good as aluminum or stainless steel," he said.
Stahl's first propeller designs used a 60% long glass fiber reinforced nylon 6 composite and testing on higher horsepower motors was successful. "When I dropped back to lower horsepower two-stroke motors, we started seeing failures," he said. "It came down to higher harmonics and vibration in the two-stroke motors."
The solution was adding a toughening agent to the long fiber composite that better dampened vibration energy, according to Stahl.
"You really have to understand the flexural modulus properties of long fiber composites when designing a propeller," said Stahl. "When I started 25-years ago there wasn't computer generated flow analysis for fiber reinforced composites. Our designs have to be slightly distorted when molded so that in use, when the blade is experiencing propulsion forces, it has the proper shape to maximize thrust."
Maximum ToughnessPiranha uses a Complēt MT series long glass fiber reinforced nylon 6 composite from PlastiComp for all its propellers. PlastiComp formulated its Complēt MT composites for maximum toughness to provide up to 40% more impact resistance than standard long fiber reinforced materials. The extra durability provided by Complēt MT long fiber composites makes them ideal for demanding applications like Piranha's propellers.
"I originally started working with PlastiComp because I was looking for a second material source – they quickly became my primary source," said Stahl. "Other long fiber materials I tried looked bad when molded. Complēt MT easily provided the surface finish I wanted for our propellers."
"I really enjoy the relationship we have with PlastiComp," he said. "Every time I have a question PlastiComp is right on the ball."
Piranha Propellers is the leader in composite marine propellers serving the recreational boating market with propellers for all major brands of outboard and inboard motors from nine to 260-horsepower.