It seems you can't read a magazine or attend a boat show lately without stumbling across some futuristic propulsion system that eliminates parts once considered vital to a boat's anatomy. While traditionalists may grumble about boats that need no rudder or propeller shaft–or steering wheel, in some cases–there are good reasons to take a closer look.

The simple truth for power boaters is that steerable "pod drives" such as the Volvo Penta IPS or the Cummins MerCruiser Diesel Zeus drive represent breakthrough technology in the recreational boating market. At a time when engine makers are making great strides in performance, pod drives represent the leading–some might say the bleeding–edge of propulsion technology.

Incubated for years on commercial vessels, pod drives do away with traditional running gear in favor of propellers mounted on swiveling "pods" that sit below the boat. The props draw power from separate engines, move independent of one another and are capable of maneuvering the boat–or keeping it still–in ways that traditional twin-engine installations cannot duplicate, even with bow and stern thrusters.

While there is still much to be determined as the few thousand "early adaptors" who own these systems put them through their paces, manufacturers claim that these units are more efficient, more maneuverable and offer better fuel economy. They also have some intriguing capabilities, such as station keeping, the ability to keep the boat steady in one place using only the drives.

While critics say these units are expensive, difficult to retrofit and vulnerable to floating debris, converts argue that pod drives will be offered as an option on scores of production boats in coming years. In fact, that list is growing past brands like Sea Ray to include more conservative companies like Silverton–and even Grand Banks.

SEA TRIAL Video by CMD shows Zeus Drive in action.

First to develop and deploy a pod drive for recreational boats was Sweden's Volvo Penta, the same company that invented the sterndrive and the dual contra-rotating prop set. Volvo's entry is the Inboard Propulsion System (IPS), which sat alone in the market for several years and has been installed on roughly 2,000 boats, according to its manufacturer.

However, it has since been joined by the Zeus system, created by Cummins MerCruiser Diesel, a joint venture of Cummins and the MerCruiser division of Mercury Marine. Zeus is only now being offered for sale, though several boat builders have committed to using it in their new designs beginning in 2008.

The two systems differ in some significant ways–IPS propellers face forward and Zeus props face backward–but both use computers to interpret the helmsman's commands and move the boat appropriately. By using differential thrust and independent pods in a twin installation–the technical term is azimuthing–the computer can move the boat directly sideways or spin on its axis without separate bow or stern thrusters.

You will hear the marketing people from each company argue the merits of forward-facing versus rear-facing props; debate the slightly different exhaust arrangements; and discuss the capabilities of the integrated trim plate that is part of the Zeus pod. But much of this may eventually be lost in the background.

The companies involved in the Pod Wars may not admit it, but the benefits to the boater from either system are similar: significantly enhanced low- and high-speed maneuverability; fuel economy improved on the order of 30 percent; and the advanced capabilities that come with electronically controlled and interfaced systems. Technology add-ons like precision autopilots and speed control also get better when connected to pod drives.

Zeus was being demonstrated at the Fort Lauderdale boat show in October, using a 2008 Sea Ray 44 Sundancer, an express cruiser design typically powered by diesels with straight shafts and props. I took a ride on the demonstrator boat to get a feel for the new system and how it might change the way we pilot.

STEERING BY STICK

Photos by Tom Tripp, Volvo Penta, CMD

Our test boat was equipped with a Zeus 3500, which is a Cummins QSB-series diesel, 5.9-liter with six in-line cylinders, producing 425 HP. It is mated to the aft-facing, contra-rotating propellers through a ZF-produced gearset that incorporates a "wet" clutch. Sometimes known as a trolling valve, the purpose of the clutch is to ease the transition in and out of gear at very low speeds.

We rode with one of the local SeaRay dealer's potential customers, Bob Henderson, of Palm City, Florida. Henderson has been buying SeaRays for more than 40 years, starting with an 18-foot inboard/outboard. Henderson said he liked the idea of simplifying his docking experience, which currently requires him to delicately back in between pilings. "I think the pod drive is the coming thing," he said.

We would soon find out.

A captain who has been participating in the Zeus test program was at the helm of our demonstrator boat and he explained how the system worked as he departed the show docks at the Bahia Mar Yachting Center. The first noticeable difference was that he was not touching the steering wheel as he left the dock. Instead, a fat joystick is used to control the system in close quarters.

With the Zeus joystick on the side panel by his right hand, he lightly nudged it forward and the big cruiser glided gently ahead. With his stern clear of the pilings, he twisted the top of the joystick and the boat rotated in place, turning 90 degrees to port in a few seconds. A gentle nudge forward and we headed out of the marina and into the waterway toward the inlet.

On our way, we paused at a bridge over the waterway and the captain engaged the autopilot to hold our position. Dubbed "Skyhook" by CMD, this autopilot uses a highly-precise GPS receiver and software to hold lateral position and maintain a selected heading. The bow swung gently one or two degrees either side of the base heading, but given that the outgoing tide had the current moving swiftly and the wind was blowing steadily out of the northeast, it was a remarkable demonstration. This is the perfect feature for holding short of a closed bridge, or maintaining position over a promising piece of bottom structure while fishing.

STANDING IN PLACE

As we moved out of the inlet, our captain mashed the conventional throttles forward and the computerized engine controls spooled up the big diesels quickly, accelerating to nearly 39 mph in a matter of several boat lengths. The Zeus joystick is automatically disabled at 1,800 RPM, with control transferred to the conventional throttles. When slowing to joystick speeds, a light hand on the stick enables it and the steering wheel automatically centers itself, as the drive pods calculate their steering and thrust requirements based on starting in a neutral position.

At high speed, the Sundancer generated significant G-forces when the helm was thrown hard over. The Zeus drives enabled the boat to carve a full 360-degree turn within approximately two boat-lengths. Outside the inlet, the seas had built to more than four feet and the northeast winds were blowing steadily above 20 knots, which made for a good test of the Skyhook position-holding system.

Skyhook had no trouble whatsoever holding the boat within a few feet of the initial position, even fully beam-to against seas and wind. Watching the propwash coming out from under the boat at bizarre angles–and different angles port and starboard simultaneously–was a little disconcerting, but that's how the system works. And on our test, it worked very well indeed, as the chart plotter confirmed our position.

Back at the docks, we opened the cockpit sole hatch to look at the engine installation. On the 44 Sundancer, there was a remarkable amount of room in the engine compartment. Our captain stepped down into the compartment and demonstrated the ease with which daily fluid checks and routine maintenance could be conducted. Perhaps even more remarkable was how far back the whole installation was in the hull. The forward edge of the engines was less than seven or eight feet from the transom, offering designers more freedom and flexibility.

ADDED SPACETom TrippAn IPS500 installed on a mockup boat hull shows how compact the installation is. Total fore-to-aft length is less than six feet.

In fact, that very issue of design flexibility brings us back to our early adopters, Silverton and Grand Banks, two companies that would not be expected to employ leading-edge technology without good reason.

Silverton Marine Corporation makes family-friendly cruising and fishing boats in the value-driven portion of the market. They are well-made and comfortable but not overly expensive. Grand Banks is the grande dame of the trawler market and its boats exude old-world saltiness. They are extremely well-crafted boats and their higher price tags reflect a level of fit and finish not universally available, but you are more likely to still find mechanical engine shifters and throttles on a Grand Banks than on many other designs, because they are simple and reliable systems that have been counted on by cruisers for many years.

Now, throw both these pictures out the nearest porthole because both companies are offering pod drives on certain models.

Grand Banks will be one of the first companies to offer a Zeus-equipped boat. The new 41 Heritage EU will debut in mid-2008 with a pair of Zeus drives hanging below its newly-designed hull. Topside, the 41 Heritage will reflect the best of Grand Banks tradition, but underwater she will sport the latest in propulsion technology. And in this case, the designers will offer a full second stateroom, made possible entirely by the compact Zeus installation.

Silverton chose to go with Volvo Penta's IPS. The company debuted its new luxury brand, called Ovation, at the Fort Lauderdale show. The 52 Ovation is an elegant, sedan bridge design coupled with three IPS500 or IPS600 systems. I managed to get a look at the boat at Fort Lauderdale and climbed down into its engine compartment, which was under a hatch in the aft cockpit. A brief examination revealed the same compact installation, again well aft, with a surprising amount of room left over for a compartment housing three big diesels.

The 52 Ovation also benefits in the stateroom department, with an remarkably roomy, full-beam master stateroom pushed aft under the salon and made possible in part by the extra room gained from the IPS installation.

CONTINUED INNOVATION

Looking ahead to 2008 and 2009, you can expect to see more and more engine/pod combinations. We have already seen Volvo Penta extend its IPS system both downwards into the gas engines and up into big new powerful diesels designed for mega-yachts.Tom TrippPhoto of a Zeus gearset and propeller pod, showing the interface between the two.

At the Fort Lauderdale boat show, Volvo introduced the new IPS750 and IPS850 (the model numbers designate the company-derived horsepower equivalent of a conventional engine), intended for yachts up to about 80 feet. The new IPS500G is an IPS unit mated to Volvo's largest gas engine, which will extend availability into the smaller express cruiser market.

We can expect CMD to make similar moves, at least in the diesel market.

Of course, fitting these systems onto new boats is no ordinary repower. Each boat hull has to be designed for–or at least tuned for–a pod-drive system, and then tested to see how close the basic software algorithms come to the desired performance goals. It usually takes scores of sea trials and software iterations to get things right. But even as you read this, builders are working with both Volvo and CMD to incorporate the pod drive propulsion systems into their model lineups, new and old. At the Miami Boat Show in February, you can expect to see several new IPS and Zeus-equipped boats debut.

And there will be more innovation in the Pod Wars. Though twin installations dominate the market, triple and quad configurations are starting to appear. Even single pod-drive installations may be possible, if a bow or stern thruster becomes part of the computer-controlled system.

The next step is what many consider to be the ultimate in pod-based technology: diesel-electric pods. Used for many years now in cruise ships and commercial applications–though at sizes inconceivable for the recreation market–recent advances by companies like Glacier Bay's OSSA Powerlite division have made diesel-electric possible for the small-boat market.

The advantage of this configuration is that it disconnects power generation from the propeller system, resulting in an even cleaner and more flexible installation than today's IPS or Zeus drives. The OSSA Powerlite systems utilize state-of-the-art, electronically-controlled diesels manufactured by Mercedes, which are mated to extremely efficient direct-drive DC electric motors. That means that the big, heavy diesel, traditionally the heart of the weight and balance problem for a naval architect, can now become part of the solution. The big diesel can be placed wherever it fits and balances best, and connected to the pod system with heavy-duty electrical cables.

So, if pod drives continue to improve and companies like Silverton and Grand Banks are already offering them as options, does that mean they are the future of marine propulsion? Time will tell. And there are many naysayers. But those who advocate these systems tend to be effusive, people like Mike Usina, vice president for sales and marketing at Silverton.

"It absolutely is the wave of the future," he said.