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Zeus adds rear-facing props to mix

Cumming MerCruiser Diesel hosted a preview and demonstration of an express cruiser outfitted with its entry in the propulsion revolution, a system called Zeus, billed by the company as the world’s most advanced marine propulsion system.

A week after my trip to Tampa for the Volvo Penta/Lazzara LSX Quad unveiling, I was back in Florida, this time at the Cummins MerCruiser Diesel slip during the Fort Lauderdale International Boat Show. CMD was hosting an invitation-only preview and demonstration of an express cruiser outfitted with its entry in the propulsion revolution, a system called Zeus.

Billed by the company as the world’s most advanced marine propulsion system, Zeus consists of a pod drive system coupled to CMD Quantum Series diesels and all controlled with a joystick, in addition to the standard helm controls. It’s become a two-company race in this propulsion arena, and the consumer ultimately should be the beneficiary.

Pod drives aren’t a new concept for MerCruiser. Its first prototype, in 1992 (before it partnered with Cummins), featured rear-facing, counter-rotating props installed in a tunnel, and used rudders for steering. Advances in technology over the years have led to Zeus, which has many similarities to those earlier prototypes but expands the current technology. In fact, Zeus offers several industry firsts, including a steerable drive mounted within a tunnel; rear-facing, counter-rotating props on an inboard system; integrated trim tabs; an integrated water intake system for accessories; and the Skyhook Electronic Anchor (more on that later).

Zeus offers similar performance advantages as Volvo Penta’s Inboard Performance System when compared to a conventional inboard drive system, including better fuel economy and handling, higher top speeds, and reduced airborne emissions and noise. The Zeus drives have bronze gearcases and midsections, and are mounted using vibration-absorbing grommets. Their twin rear-facing, counter-rotating stainless steel props increase blade area, enable the use of larger gear ratios, eliminate side forces or “prop walk,” and minimize cavitation.

I’m certain there will be a continuing debate over the advantages of forward-facing props found on Volvo’s IPS versus the rear-facing props on Zeus. Robert Mirman, CMD manager of strategic planning and one of the on-board technical advisors during our demo ride, says that although forward-facing props are more efficient by running in cleaner, undisturbed water, that advantage is negated by the additional form drag created by high-pressure water passing over the gearcase lower unit, or “torpedo.”

And Zeus design engineers stress that rear-facing props provide a measure of safety over the forward-facing configuration. Mirman says that if an underwater object is struck, it likely will be deflected downward by the keel and skeg, away from the props. In the event of a substantial underwater impact, the skeg is designed to shear below the torpedo, minimizing damage to the drive. If there was a major collision above the keel depth, the gearcase is designed to shear away without compromising the hull’s watertight integrity.

CMD mounts the Zeus drives in tunnels, reducing vessel draft and keeping the pods’ torpedoes at the same depth as the keel. Tunnel-mounting also raises the thrust vector, helping reduce bow rise by decreasing leverage. In addition, tunnel-mounting will allow Zeus to be fitted to existing boats that already incorporate the tunnel configuration.

Zeus features an integrated trim control system consisting of a sizable hydraulic trim tab on each drive. The tabs are controlled by an automated trim control system and include a manual override at the helm. The automatic system was used during our demonstration ride, compensating for bow rise and vessel list as required. To fully appreciate the automatic mode, the trim tabs were placed in manual mode for a moment, with predictable results: More work was required, and you’re correcting a problem that’s already occurred.

An exciting feature common to both IPS and Zeus is joystick operation, which simplifies vessel control at low speed and is especially useful in critical docking maneuvers. Low-speed, close-quarters maneuvering can be easily mastered with the use of Zeus’ intuitive joystick, which proportions and directs thrust as required. As an additional aid to low-speed maneuvering and control, CMD has incorporated trolling valves and exhaust water diverters into Zeus. Technology has all but eliminated the days of independent shifting from forward, neutral and reverse, while feathering the throttle and occasionally adding some steering wheel input.

The Zeus joystick is comfortable to operate and provides good directional control over the boat. By rotating the upper portion of the joystick, you are able to rotate the boat on its axis without the use of bow or stern thrusters. With a little practice I was able to back the express cruiser diagonally aft, toward the port quarter, and then completely spin the boat around without ever looking at the controls.

A feature unique to the Zeus joystick is its automated station-keeping ability using the so-called Skyhook Electronic Anchor. When connected to a GPS and heading sensor, the system has the ability to maintain the vessel on a fixed heading within a tight area, even in strong currents and wind. Details on the accuracy of this system were unavailable, but it will be dependent on GPS accuracy, system response time, and sea conditions. I was able to experience the boat holding position in a busy, rough channel with far greater accuracy and much less drama than would have been possible with conventional manual controls.

The pod drives feature electro-hydraulic steering, which claims stronger, more reliable and faster response than electro-mechanical systems. The steering “feel” is variable, allowing the system to be tuned for different operator preferences, such as self-centering, number of turns from lock to lock, ease of turning, and feedback felt by the operator.

CMD has built system redundancy into the electronics controlling Zeus. There are multiple potentiometers for throttle and shift control, triple-redundant busses for the primary propulsion functions, and electric backup pumps for pod rotation.

Although we tested a preproduction model, Zeus is scheduled to be available beginning with model year 2008 boats. CMD plans to offer it with Quantum engines from 330 hp to 550 hp, and a built-in autopilot that can interface with NMEA 0183 chart plotters will be available. CMD says it will be offering vessel demonstrations to the public at the Miami International Boat Show, which runs from Feb. 15 to 19.