America's Definitive Marine Engine Magazine
The direction of marine propulsion has taken a sudden and tantalizing twist with the recent introduction of a module that combines the best design elements of inboards, sterndrives and outboards with a jetdrive.
Known as the JetPac, this new hybrid mounts its engine inside a pod that´s bolted to the transom. Self contained, there's no transom cutout or universal joints. Neither is there an exposed lower unit, trim/tilt rams, drive shaft, strut or propeller. Instead, with the essence of simplicity, a waterjet lies cocooned inside the protective pod.
Literally an extension of the hull, the JetPac pod is buoyant, with broad shoulders that spread the module´s weight over a wide surface area. That means a rock-solid footing that´s the next best thing to one piece construction. But the real beauty of the the pod is the way it frees up a considerable amount of cockpit space at the same time it extends the planing surface of the hull. That greater LOA improves the ride and increases top speed. Unlike an outboard motor, but admittedly the same as a freshwater cooled inboards and stern drives, the cooling system is isolated from the corrosive effects of raw water.
As for performance, I've driven the JetPac twice. Both tests were conducted on a 19 foot KeyWest bay boat rigged with an International Engines HS 2.8 liter inline 4 cylinder diesel. Turbocharged and intercooled, the motor is rated 150 horsepower at 3,600 rpm. Bouncing around on Biscayne Bay, I was mightily impressed with the efficiency of the large diameter jet pump.
Time to plane was short. Acceleration was particularly quick for a diesel. Reverse thrust also proved exemplary due to the large size of the articulating bucket. Out of the water it looks just like the reverse-thrust mechanism of a jet engine like you have probable seen out the window of a Boeing 747 during landing. The large diameter of the JetPac pump flows a big volume of water at all engine rpm. The payoff comes in crisp, quick steering both on plane and at idle speeds. Docking was easy.
Besides the diesel there´s also a 275 hp Chevrolet Vortec 5.7 liter, V8 with electronic fuel injection. It burns cheap the cheap staff, unleaded gasoline. Intended for boats measuring from 16 to 25 feet, the JetPac make eminently good sense for re-powering or for original installations. Zodiac and Key West Boats have already integrated the JetPac into their product lines. Both companies have begun building boats specifically designed to take advantage of the systems.