BRP recently announced the addition of a fourth model to its line of Evinrude E-TEC Pontoon Series outboards, designed specifically for pontoon boats, a 1.3-liter triple-cylinder motor rated at 65 horsepower which will be available early this spring. The Evinrude Pontoon Series already includes 90-, 115- and 150-hp models.
So what, you might be wondering, makes an outboard motor “pontoon-able?” The main challenge is creating thrust in the very turbulent water that’s created directly behind the boat. A V-hull boat can be designed to direct a flow of clean water to the propeller of an outboard or sterndrive, so the prop and outdrive can be located relatively high and trimmed even higher at speed, to reduce drag. In contrast, the water flowing off a pair of pontoon logs creates a real froth at speed, as the inner wakes converge forward of the “transom” and can even be agitated by contact with underside of the deck. On triple-log pontoons, the center tube tends to plow a trough in the water right in front of the motor. Some pontoons are equipped with lifting fins or planes along the length of the tubes, designed to raise the boat at speed, which make the thrust problem worse by also raising the prop. Most builders design the motor bracket with a shape intended to improve water flow to the prop. Really big pontoons, like the Premier 290 can be rigged with twin motors positioned behind the outboard tubes, much as a fiberglass catamaran is powered.
A key to good pontoon performance is getting the prop as deep as possible in the water behind the boat, where it has a chance to bite on solid water, and running a propeller with a lot a blade area. That big prop also delivers more thrust to control the boat at off-plane speeds. A pontoon loaded with passengers has a lot of mass, which can overwhelm a prop that’s too small when trying to maneuver at a dock, for example, or in a windy situation.
The Evinrude prescription includes a lower 2.38:1 gear ratio (rather than the standard 2.0:1 ratio) that helps the motor handle a bigger prop, and special motor mounts that reduce vibration on pontoon installations. The 65 Pontoon Series is also offered with a 2.25-gallon remote oil reservoir that BRP says extends time between fill-ups to 100 hours and makes it easier to check and refill the reservoir on a pontoon.
Mercury recommends its FourStroke BigFoot
models at 40, 50 and 60 horsepower for small to medium-size pontoons. Equipped with the same gearcase as its 115 FourStroke outboard and a 2.33:1 gear ratio (compared to the standard 1.83:1 ratio), the BigFoot model can run a larger-diameter prop with more blade area, and the longer gearcase puts that prop deeper in the water. These motors also have an over-size anti-ventilation plate that reduces prop slip during low-speed maneuvers.
Yamaha HighThrust F50 and F60 model outboards also have a 2.33:1 gear ratio (standard ratio is 1.85:1) and can be equipped with a Yamaha DualThrust propeller that directs exhaust away from the blades to reduces ventilation, especially in reverse, when a standard prop is essentially backing right into its own exhaust.
A larger gear case, and a bigger prop with generous blade area, will generally reduce top speed and efficiency on a vee-hull boat. On a pontoon, these factors will conspire to deliver more control and efficiency with little impact on top speed, which really should not be the main concern of weekend pontooner anyway. Look at manufacturer recommendations for a good pontoon prop to match the motor you are running. You want a lot of blade area for thrust, and a design that’s happy running deep in the water – a prop with a lot of blade rake that’s designed to run at high trim angles, for example, is exactly the wrong prop for a pontoon.