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May 28, 2010

Pods or Props?

Pod propulsion represents the most significant step forward in boating since the propeller

You can count the truly innovative leaps in recreational boating without using all your fingers: the modern propeller, fiberglass, outboard power, diesel inboard, loran, GPS, electronic chart plotting. Each of these has generated an increase in the number of recreational boaters and their comfort levels. Most other technology qualifies as incremental improvement.

Since the late 1990s, a propulsion system previously seen only on tugboats and cruise ships has been introduced to recreational boating. Pod (short for "azipod") drives feature two or more "pods" sticking straight down from the hull that possess the ability to turn independently. With this system, you can maneuver your boat in any direction you wish without the benefit of bow or stern thrusters.

Currently, three companies produce azipod propulsion systems for recreational vessels: Cummins MerCruiser Diesel (CMD) has Zeus for inboard and Axius for stern drives; Volvo Penta makes IPS (Inboard Performance System); and ZF has its Pod Drive System. All three utilize dual propellers turning in opposite directions on each pod. Also in common, they all use four-blade inner propellers and three-blade outer props.

Volvo Penta places the props on the forward end of the pod, pulling the vessel, while CMD and ZF mount the props on the after side to push. The advantages of dual, counter-rotating props include the elimination of rotational losses and lateral forces as well as greatly reduced cavitation. Increased blade area also allows higher gear ratios for even greater efficiency. Boats track straighter in both forward and reverse.

CMD's Zeus and ZF's pods both have built-in trim tabs. Zeus drives can now be paired with a number of other manufacturers' engines, such as Caterpillar and Yanmar. Expect more engine companies to come on board as pod acceptance grows. Zeus accommodates up to 600 hp engines and utilizes Mercury Marine's proven DTS (electronic) controls that include remarkable engine and systems monitoring. Zeus comes with the most features included as standard, including dynamic positioning and auto-trim.

ZF - a transmission company at heart - supplies only the pods to match with virtually any engine you choose, be it gas, diesel or diesel electric. Its pods accommodate up to 1,200 hp. ZF also offers a propulsion system (called JMS) for standard prop-and-shaft vessels that affords the same joystick-maneuvering abilities as IPS and Zeus, but with only standard propulsion and a bow thruster.

Volvo Penta's IPS system works only with Volvo power. Currently, it can be paired with engines up to 900 hp. Volvo Penta charges extra for many of its features such as dynamic positioning and auto-trim (though, unlike Zeus, trim tabs are an un-integrated separate system on boats with IPS). IPS also comes with Sport Fish mode, a high-speed, fish-fighting maneuvering function.