POD Power

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IPS and Zeus take the dread out of docking, while greatly improving boat performance

IPS and Zeus take the dread out of docking, while greatly improving boat performance

They’re the propulsion systems everyone is talking about, and for good reason. Pod drives — Volvo Penta’s Inboard Performance System and Cummins MerCruiser Diesel’s Zeus — are a true boating breakthrough, improving handling and fuel efficiency and making for all-around simpler operation.

“Pod drives in general are changing the industry,” says Kurt Bergstron, manager of mechanical engineering and quality control at Cobalt Boats, of Neodesha, Kan. “[They’re] helping people move into larger boats.”

How good are the pods? Volvo and Cummins MerCruiser claim their respective systems raise fuel efficiency by up to 30 percent, boost top-end speed by 20 percent, and increase acceleration by 15 percent. From what I’ve seen — and I’ve had the opportunity to test both systems — these claims aren’t unrealistic.

Pod drives also deliver much-improved turning efficiency and response. Specific numbers vary with each application and manufacturer, but without question there are substantial improvements on all performance fronts. Both IPS (www.volvo.com ) and Zeus (www.cmdmarine.com ), for example, reduce airborne emissions and noise by venting the exhaust underwater.

“Fabulous handling — nicer than the jet-drive boats we have previously owned,” says Debbie Gorlin of Destin, Fla., of her IPS-powered 2006 Tiara 4000 Sovran. The Gorlin family elected to go pod because Debbie, who operates the boat while her husband tends the lines, “did not want to figure out the close-quarters maneuvering with conventional shift and throttles.” The drive manufacturers and boatbuilders don’t believe Debbie Gorlin — who with her husband has owned seven boats — is alone in her wishes.

The pod’s hydrodynamic shape creates much less drag than conventional inboard propulsion with its inclined shaft, strut and rudder. The systems also create horizontal thrust, which means the full power of the engines is used to drive the boat. That thrust, combined with the steerable pods, provides directional control at slow speeds as soon as the boat is put in gear — unheard of in conventional propulsion systems, even after bow and stern thrusters have been added. A conventional inboard system requires prop wash to be directed by a rudder and needs the boat to be under way for steerage. It also is less effective when operating in reverse.

The joysticks that are part of the Zeus and IPS systems enable the operator to control the boat in slow-speed maneuvers. The features differ slightly, but the same basic principals apply to each.

“When we travel, we do a lot of docking where there are currents running,” Gorlin says. “I am able to confidently dock our boat where others with smaller boats give up and leave.”

The difference is the intuitive joystick operation, which provides directional and speed control. If you want the boat to go directly to starboard, just push the joystick to the right. To go to port, just push it left. You can even move at an angle, such as forward and to starboard at the same time by moving the joystick accordingly. Minor midcourse alterations are just as simple.

Pod drives get the boat up on plane quicker and at lower speeds, with less effort than conventional inboards. The prop shafts on conventional inboards typically are inclined down between 11 and 14 degrees and tend to push the stern of the boat upward. Counter-

rotating props on both Zeus and IPS eliminate the rotational loss experienced with a single prop and minimize cavitation. Pod-equipped boats also aren’t susceptible to side forces, which create prop walk. Increased blade area resulting from the use of dual props allows for larger gear ratios.

Both IPS and Zeus are complete packages, meaning one manufacturer is responsible for all your propulsion needs, repairs and warranty work. Each of the systems is installed through a single opening in the hull. That one opening handles exhaust, seawater intake for engine and accessories, steering, cooling and propulsion. This eliminates the multiple through-hull fittings and valves that typically perforate a powerboat hull below the waterline.

Concerns with engine alignment are also a thing of the past. The new systems are close-coupled, or nearly so. Pods are mounted within large rubber grommets, which isolate gear noise and vibration and help prevent it from being transmitted throughout the hull.

Some say a pod-driven boat is more susceptible to serious damage in the event of a grounding or impact with submerged objects. In fact, however, the pods of both systems are designed to shear away from the hull without compromising watertight integrity. That means pod drives usually can be repaired more easily than conventional inboard systems.

The engine and upper pod unit remain intact above the hull opening if the lower unit shears off. That unit is designed to be replaced in its entirety, and the repair is much easier than replacing a rudder, prop shaft, strut and the associated stuffing boxes of a conventional inboard system, all of which typically sustain at least minor damage from an impact, according to the manufacturers.

At Cobalt Boats, Bergstron says more than 400 hours of offshore testing and development went into the new Cobalt 46, equipped with twin Cummins MerCruiser Diesel QSB 480 engines and Zeus pod drives. Part of that testing was a validation of the breakaway feature incorporated into Zeus.

Zeus has been tested on soft groundings and hard impacts. The pod was sheared off by hitting a solid submerged object at high speeds without damaging the hull or affecting watertight integrity. In other testing the pod was sheared off on a sandbar at high speed, then retrieved and cleaned. It was then reinstalled and run on the boat without issue, according to Bergstron. I have seen an underwater video of these tests, and it is certainly convincing.

The debate over forward-facing props vs. rear-facing props is a standoff. The forward-facing props on Volvo’s IPS operate in clean, undisturbed water for more efficiency, but they increase form drag, which is created by high-pressure water passing over the gearbox lower unit, or torpedo. Zeus’ rear-facing props don’t have the undisturbed water to operate in, but they don’t create form drag. Zeus design engineers contend rear-facing props provide a measure of safety over the forward-facing configuration. Both manufacturers tend to agree there are two different ways to accomplish the same thing, and neither is a clear winner.

Both IPS and Zeus are referred to as fly-by-wire systems, requiring no mechanical connection between throttle lever, gearshift, steering wheel, joystick and engine. All system commands are electronically transmitted. The systems have full redundancy built in, should any of the control systems fail. Steering on each is adjustable for feel and rate.

Zeus highlights

Zeus is the result of a team effort between Cummins MerCruiser Diesel, Mercury Marine and Mototron. CMD provides the high-tech, clean-running diesels, Mercury Marine brought in its decades of expertise with underwater drives, and Mototron links it all together with its expertise in electronic controls and networking systems, such as SmartCraft.

The first prototypes appeared in 1992, featuring rear-facing, counter-rotating props installed in a tunnel but using rudders for steering. The tunnel remains, along with the rear-facing, counter-rotating props, but steering utilizes independently articulating drives instead of rudders.

“Zeus provides a high level of protection to the pod and propellers by using a tunnel design,” says Cobalt’s Bergstron. “By vertically mounting the pod in a tunnel, CMD has significantly reduced exposure of the pod to submerged objects. A breakaway skeg and rear-mounted propellers are additional levels of pod projection. The Zeus design is focused around making it difficult for the pod to sustain an impact significant enough to shear it from the boat.”

Zeus pods feature electro-hydraulic steering, claiming stronger, more reliable and faster response than is possible with Volvo’s electric motor acting on planetary gears. An integrated auto tab feature on Zeus uses high-velocity water exiting the tunnel to impact on the trim tabs for control, and protects the aft portion of the hull from impact if the drive shears off. The auto tabs can be programmed to automatically trim out bow rise and optimize the trim for speed and fuel consumption. They work in both the planing and deceleration phases of operation. The Cobalt 46 runs at 4 degrees, and maximum bow rise is 8 degrees during acceleration, says Bergstron.

The Skyhook Electronic Anchor feature maintains the boat on a fixed heading within a tight area, allowing you to set lines and fenders, tend to fishing gear, relax a bit while waiting for bridge openings and fuel docks, or just hang out in one place without having to drop the lunch hook each time. The accuracy of your maintained position depends on the accuracy and consistency of the GPS signal the boat receives.

Zeus is available in two packages — the 3500 and the 3800 — offering power options from 330 hp through 540 hp. It is being installed by Sea Ray, Cobalt, Grand Banks, Doral and others.

IPS highlights

IPS was introduced in October 2004 and has been evolving since. It is designed for twin-engine installations aboard planing powerboats from 30 to 80 feet with speeds of 25 to 45 knots. Just nine months after its introduction, Volvo reported that IPS was on production lines for 44 different powerboat models.

The IPS package should be available in eight sizes from about 250 hp to about 670 hp (IPS 350, 400, 450, 500, 600, 750, 850), as well as the IPS 500G, a 375-hp gasoline engine. Each is named for the engine horsepower that would be required of conventional systems to provide the same performance. For example, the IPS 350 relies on a modified version of Volvo’s 260-hp D4 common rail diesel, but performance would be comparable to a conventional propulsion system using a 350-hp engine. The IPS 600 uses the 435-hp version of the company’s D6 engine while offering the performance of a 600-hp conventional system.

Last June, at its media briefing in Sweden, Volvo introduced the IPS 750 and 850. The two new units are both physically larger and stronger than their predecessors to handle the additional horsepower and torque created by the new engines. The company also introduced the IPS 500G, a gasoline system designed specifically for the U.S. market. It is based on the GM 8.1-liter “big block” V-8, and is said to be 30 percent more fuel efficient than traditional gasoline-powered boats. The engine is rated for 375 hp at 4,400 rpm and sports an optimized gear ratio of 2.4-to-1.

Volvo wants to be certain its system’s performance lives up to its potential and, therefore, will not allow installation of IPS in a hull that has not undergone extensive testing and evaluation by Volvo’s engineering team, which leaves nothing to chance. Volvo worked extensively with Lazzara Yachts, which designed and built the Lazzara 75, a quad IPS 600 installation that was unveiled in October 2006. The yacht made its debut with Volvo’s joystick control, which has since become available with all Volvo installations. This 75-foot yacht gets up on plane at a mere 12 knots and has a full-turn radius of 186 meters, as opposed to 436 for the same vessel with conventional propulsion.

Most recently, after extensive work and testing with Volvo, the first IPS-powered center console, the SeaVee 390, is complete and was to have debuted at the Miami International Boat Show, according to Jorge Alfonso, vice president of SeaVee Boats, of Miami. Other IPS boats include Chris-Craft, Luhrs, Carver, Cruisers and others.

Volvo has developed a “GPS Anchor,” which it describes as an emergency brake at sea. When equipped with the joystick, the GPS Anchor coordinates the IPS to maintain the boat in its current position. The joystick also can have up to four remote “joystick docking stations” added, allowing low-speed vessel control from anywhere on board.

What I found to be the most impressive addition to the IPS is the “Sport Fish Mode,” which through unconventional (as we have come to know) pod-drive orientation allows the vessel operator to move just the stern of the boat sideways in either direction with the powerful engine thrust. This allows incredible maneuvering capability in reverse to back down on fish.

Calyber was the first fiberglass Carolina sportfish builder to tool up for the IPS installation. I spoke with Jim Machniak, who has had his Calyber Express 35 offshore from the Carolinas, through the Florida Keys and up through the Erie Canal into Lake Erie. An experienced angler, Machniak has operated everything from center consoles to small sportfishing boats and Rampages.

“The Calyber with IPS has the speed to match center consoles, with better handling and efficiency, reports Machniak, a 28-year-old hedge fund trader who lives and works in Chicago. “Other diesel-powered vessels of similar size could not compare with it. Offshore fishing with the IPS joystick and Sport Fish Mode was great. You can put the boat exactly where you want it and quicker than everyone else.”

I have spent time on the water both with Volvo’s IPS and CMD’s Zeus. The two systems differ in many ways — some subtle (variations in joystick operation), others pretty broad (direction the props face). Each company has brought its own flavor of technology to the table.

Two things are certain: Pod drive systems are here to stay, and both Volvo Penta and CMD will continually be raising the bar for one another. The ultimate winner will be the boating public.