The  "Power-Vent" Integral Vented Surface Drive System

The "Power-Vent" integral vented surface drive is designed for high performance boats. It’s uniqueness is that it can position high efficiency surfacing propeller technology under the hull of a vessel using simplistic, more conventional marine hardware without transom projections and the need to trim shaft angles. The system accomplishes this by configuring a super-cavitating surfacing propeller mounted on a fixed shaft supported by a strut with a stuffing box enclosed within a specially engineered tunnel that is molded into the boat’s bottom. At the forward edge of the tunnel is a short vertical step, which causes the planing wake to occur about 4 feet ahead of the transom. Since the propeller is located completely under the hull within the tunnel, air is introduced to over come other wise detrimental water flow to the prop that would occur. The air allows the planing wake to happen at the vertical step for true “surfaced” operation. Air is provided via two ducts running longitudinally either side of the propeller tunnel. The demand of the spinning propeller acting like a fan, and the flow of water ejected from of the prop tunnel causes air to be sucked in through vents in the transom, and delivered through these ducts to in front of the propeller. The engine’s exhaust is also discharged into this region ahead of the propeller, which is ejected out in the prop wash, resulting in reduced noise, smell and soot.

The ceiling of the tunnel slopes gently towards the front acting like a baffle to direct thrust forwards when reversing, resulting in good reverse authority. Steering is accomplished by a balanced rudder situated aft of the propeller which provides a quick high-speed steering response. For single engine applications, docking maneuverability is enhanced with a bow thruster.

One of the major benefits of the integral vented surface drive is its inherent ability to provide the correct amount of ventilation or immersion of the propeller with out operator input. Because a surfacing propeller is designed to run half out of water too much immersion tends to over load the engine to the point where it falls below its torque range. Too little immersion and the engine will over rev as the prop simply aerates the water. This can be the case with other surface drive systems, requiring the units to be constantly trimmed up or down while the craft gets on step. They create a situation where the craft cannot steadily operate at any speed in the range from just below the planing to fully planing phase. Typically this range is between 12 to 20 knots. The result is either the craft operates in the displacement mode or in the planing mode and has trouble in the transition phase between these two.

Thie Power-Vent surface drive is a non articulating or fixed design that provides it self with the correct amount of immersion of the propeller through its vents and ducts. The ambient water level acting like a valve on the vent opening automatically regulates the volume of air entering the prop tunnel. The greater the boat’s speed the greater the need for air in front of the prop. As the boat accelerates and begins to lift, the water level over the vent opening begins to drop. This allows the flow of air to gradually increase until the craft has reached full planning at which time this duct opening is now fully exposed allowing maximum airflow. At slower speeds this “water valve” creates a restriction in the airflow, which again causes the correct amount of prop emersion to prevent over revving and excessive cavitation. What this ability allows is the boat and the propulsion unit to work together as a system, providing the capacity to produce a given speed for a given engine rpm. A craft is able to remain at any of the transitional speeds with proper loading of the engine.

Additional benefits this drive has over other surfacing and out-drive units is that it is truly simplistic with minimal moving parts and low upkeep requirements. There are no U joints, rubber bellows, sensitive seals bearings and gears, oil filled housings, external hydraulics and hoses for steering and trim etc. or corrosion susceptible parts, none of which are well suited for their demanding marine environment. 

The bottom line is that a surface drive surpasses the efficiency of any other drive system available. Typically an efficiency gain of 10-20% is recognized over Out-drives, Inboards, or Water Jets.