CVT use in Outboard Marine Engines

Boaters typically measure performance of their motors in two competing categories: “hole shot,” which is the power available to accelerate and plane off the boat, and overall top speed. As outboard engines do not have a multi-speed transmission like a car does, there is a constant compromise between a fast powerful start and hair ripping top end speed. The device at the heart of this compromise is the propeller. Using a lower pitch, the boat gets more acceleration on the low end, but top speed is reduced. Increasing the pitch provides a higher top end speed, but also increases the time to get to that speed and, more importantly, to get the boat on plane.

Typically, boats rely on the prop “slipping” while they are accelerating. This is part of the compromise where the prop pitch combined with the engine RPM and boat speed are at odds with one another. If a greater gear reduction existed between the engine and propeller (around a factor of 2), then the engine could deliver higher torque (and better acceleration) at a lower prop RPM. As a result, the whole system would be much more efficient. The Milner Continuously Variable Transmission is ideally suited for this application, and its highly compact, in-line design allows integration into existing outboard motor configurations without significant housing or drive shaft modifications.

How a Milner CVT Can Optimize Outboard Motor Performance

The MCVT can deliver smooth, step-less shifting over its entire ratio range while the outboard motor operates at its maximum torque output. This delivers the motor’s full torque to the propeller at a lower rpm and provides the boater the hole shot of a low pitched prop. Then, shifting the transmission ratio as the boat planes off, the outboard motor is able to deliver high rpm to the prop and move the boat at a top speed associated with a higher pitched propeller. This allows the boater to choose his propeller based on top speed performance without compromising low speed power.

The Milner Continuously Variable Transmissions can provide boaters with better acceleration and higher top end speed by allowing the propeller and engine to run at the optimal gear ratio for each condition.