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New propulsion system uses pod drives

Cummins MerCruiser says its Project Zeus will offer better handling, speed and fuel economy

Cummins MerCruiser says its Project Zeus will offer better handling, speed and fuel economy

Cummins MerCruiser Diesel of Charleston, S.C., recently unveiled Project Zeus, a self-contained propulsion system for recreational boats that uses steerable pod drives patterned after those on large commercial ships. The twin gearcases mount through the bottom of the boat and provide directed, horizontal thrust. At low speeds the system’s software translates inputs from a joystick controller into the independent operation of the drives, for close-quarters maneuverability comparable to a bow or stern thruster, according to the company.

The basic design calls for pod drives mounted through the hull bottom in tunnels. The drives have counter-rotating, aft-facing propellers; integrated trim tabs; and Mercury’s SmartCraft digital throttle and shift technology.

The system in many ways is a competitor to Volvo Penta’s Inboard Performance System, introduced last year, but differs in several respects.

“Pod drives have been around in commercial boating for many years, decades even, and what you see now with Volvo Penta [IPS] and CMD and Mercury is you can do it at a price point where it’s possible,” says Rob Mirman, project manager for Project Zeus.

Advantages of Project Zeus over conventional inboards, according to CMD, include better handling, speed and fuel economy; intuitive joystick control around the dock; station-keeping; and “automotive-level” vessel integration.

Project Zeus, which will be available for the 2008 model year, was first tested in 1992, according to Mercury Marine. The prototype pod drive used counter-rotating propellers in a tunnel, like the current system, but had rudders for steering. In subsequent versions improvements such as steerable drives, joystick control and integrated hydraulic trim tabs were added.

Designed for boats from about 35 to 48 feet, Zeus also incorporates technologies developed in other Mercury projects, including rubber grommets from Sport Jet drives that reduce gear noise and vibration at the hull-to-drive connection, SmartCraft systems networking technology, and digital throttle and shift. Zeus uses CMD’s Quantum series common-rail electronic diesels and through-hub exhaust. Power options range from 330 hp to 500 hp.

The pod drives have bronze gearcases, and a skeg beneath each gearcase torpedo is designed to shear off in the event of a collision. Since the drives are mounted in hull tunnels with the torpedo at the same depth as the keel, the upper portion of the drive is protected. In a catastrophic collision the entire gearcase will break off instead of breaking the boat bottom.

The tunnels also facilitate shallow draft, and Zeus’ stainless steel counter-rotating props are mounted aft on the gearcase. Volvo Penta’s IPS has aslightly different configuration, withforward-facing “puller” props and no tunnels for the drives.

CMD says Zeus pod drives result in 30 percent fuel savings and 7 percent faster speeds than conventional inboards. The system takes advantage of horizontal thrust rather than the angled prop shafts of conventional inboards, as well as the hydrodynamic shape of the pod drive as opposed to a shaft, strut and rudder. The drives can rotate to an angle of outward thrust of 45 degrees, and inward to 15 degrees.

With its independently moving drives and joystick control, Zeus is designed to make docking easier without bow and stern thrusters. The joystick is in operation when the boat is put in neutral. The system can move a boat sideways, and rotating the knob on the joystick spins the boat. More power is added as the operator moves the joystick off-center, and the system slips the clutch automatically so that it doesn’t simply take off in gear, Mirman says.

“You just push the joystick in the direction you want to go,” he says. “We’ve had a lot of people with no boating experience … who’ve felt very comfortable docking a 42-foot boat with the joystick.”

Zeus’ station-keeping feature links to a GPS system to keep the boat in place on a fixed heading when not under way, despite wind and current. Mirman says it would be handy for fishing or waiting at a busy fuel dock or lock. “You can pull up to a dock and step off without tying up,” Mirman says of the test boat’s station-keeping precision.

Under way, Zeus takes advantage of the steerable pods for enhanced maneuverability, according to CMD. The helm has a self-centering wheel with digital fly-by-wire control and a customizable “feel” depending on boat type.

“For example, when you turn the steering wheel you can have a more aggressive response or a more passive response,” says Mirman, noting that a Fountain go-fast could be set up differently from a Tiara or Azimut cruiser. “It’s kind of like the difference between the Cadillac feel and the Porsche feel in the steering system.” The wheel’s self-centering feature can be disabled if desired, he says.

The system also uses Mercury’s proprietary SmartCraft connectivity throughout the boat, so the operator can monitor integrated systems, including engine performance, generators, air conditioning and navigation.

Zeus’ autopilot can be linked to a chart plotter and will support traditional autopilot functions, automatic trim, and tight area and fixed-heading station-keeping. It likely will be offered as an option when Zeus goes to production, Mirman says.

Each pod drive unit is designed to install as one piece with limited through-hulls, minimal engine alignment, and an integrated water intake system for engines and accessories such as air conditioning.

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