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Is pod propulsion a viable choice?

Sep 10, 2013
Sabre Yacht’s line of power vessels, Back Cove Yachts, makes use of pod propulsion systems.

Sabre Yacht’s line of power vessels, Back Cove Yachts, makes use of pod propulsion systems.

Back Cove Yachts/Billy Black

Editor’s note: Podded propulsion has been around for some time in the commercial world, but how effective is this type of drive setup for power voyaging boats? Ocean Navigator contributing editor Twain Braden reports on the pod drive approach.

My appointment with Bentley Collins of Sabre Yachts was scheduled for 0800 on a recent summer morning. It was a balmy day on the Maine coast, a slight breeze riffling the waters of Casco Bay. I had inured myself to the likelihood of being snowed by a pushy salesman eager to show off his superior product.

Collins was anything but. In fact, he had the casual air of the car salesman in the 1980s Honda commercials who seemed reluctant to say anything since he knew the product didn’t need salesmanship. Collins conveyed Honda’s slogan — “the car that sells itself” — in manner and word.

After a brief tour of the 38-foot Sabre powerboat, he started the twin diesels, slipped out of the plush captain’s chair and told me to go for it — take it off the dock and out into the river. Just as casually, he stepped off the stern onto the dock and released the lines. This was a brand-new vessel, and we were surrounded by similarly gleaming boats in a tight slipway, one boat just three feet forward, and another about the same distance astern. And Collins knew nothing about my boathandling abilities.

Sabre Yachts

A pod drive unit during installation.

I pressed the joystick to starboard, at a 90-degree angle, and there was a low growl followed by an exciting lurching feeling, and the boat suddenly moved perfectly sideways. I pressed it diagonally; it responded just as smoothly, zipping at a 45-degree angle to a spot in the center of the slipway. Soon I was exiting the slipway more smoothly than I ever had on any boat anywhere. Once in open water, I pressed the throttles forward and took hold of the wheel. Instantly, the joystick disengaged and I was essentially driving a conventional twin-screw boat — albeit with the handling of a Porsche. I felt like a criminal getting away with something.

I tooled around Portland’s Fore River for a few minutes, nosing up to various objects, driving recklessly through patches of floating seaweed, attempting to put the boat through her paces. But really there was nothing to it. Once the novelty wore off, it was almost boring. The boat simply did exactly what I asked it to do with minimal effort.

“Handling a LOA boat of 58 feet with only two people on board in an array of cruising experiences has been wonderful given the command authority the pods provide,” said Jeffrey Harris, owner of a Sabre 54 with a pair of Volvo Penta IPS pods. Harris keeps the vessel in Annapolis, Md., but last year took it to Lake Champlain, where he navigated the vessel through numerous locks — all without significant challenges.

Harris had the vessel delivered by truck from Sabre’s yard in Maine, requiring removal of the pods for shipment for bridge clearance. Once in Maryland, the pods were reinstalled in a few hours, Harris said. (The only glitch he reported was an annoying alarm that was apparently caused by a software problem, a situation that did not affect operation of the boat, he said. Harris said the company replaced the secondary joystick and engine software — warranty items — and the problem was solved.)

John Anthony Ferro, whose sails his 48-foot Sabre out of Portland, Maine, has a similar love affair with his pod system.
“I bought the first Sabre with pods, the Sabre 42, but I was an inexperienced boater at the time. This boat quickly made me a legend at docking maneuvers. I put this boat in places you wouldn’t believe,” Ferro said. “I wouldn’t buy another boat without pods.”

Sabre installs Volvo Penta on its smallest model (38) and its largest (54) and the Cummins MerCruiser Zeus system on its two mid-size ones (42 and 48). (Cummins builds the engines; Mercury builds the pod units.) This was because Cummins was first in offering an entirely integrated system, positioning software, trim tabs, and autopilot. Volvo Penta has since filled in the gap in its offerings, offering fully-integrated systems at every size. Volvo Penta propellers face forward; Zeus props face aft.

Ferro is especially gleeful about the Zeus Skyhook system, which integrates DGPS positioning with the propulsion system at the touch of a button. This is identical to the positioning system used by the U.S. Coast Guard on its buoy tenders. The DGPS position is entered into the computer, and the vessel stays in position as the buoy is deployed in the exact position, give or take three feet, that the chart says it should be. When approaching a dock, Ferro stops about 30 feet away and then presses the Skyhook button. He then retrieves and positions docking lines and fenders as the system keeps the vessel perfectly positioned, counter-acting the effects of wind or current. When he’s ready, he slips back into the chair and simply maneuvers the boat sideways into the slip.

Volvo Penta

The Volvo Penta drive units with their contra rotating, forward-facing props.

He owned a 38-foot Sea Ray previously with twin screws and a bowthruster and said he was nonetheless anxious about maneuvering the vessel in tight quarters.

Committing to pods required retooling everything at Sabre, according to Collins, since the lack of propeller shafts means you have to isolate the engines all the way at the stern, which significantly changes weight distribution. The designer increased the hull’s buttock angle, thereby increasing volume in the stern to accommodate the extra weight aft. This design change means the propulsion equipment is in a single, consolidated engine space beneath the aft deck, and the interior of the boat gained an extra cabin at the same time.

The other benefits of pods, besides maneuverability, are, of course, fuel efficiency and more horsepower from the engine, since the propeller shafts are in parallel with the hull. Consequently, Sabre describes its engine models by the amount of power a conventional-drive propulsion system would deliver. A Sabre 38, for example, carries the IPS 400, which is really a 300-hp engine, since the prop can deliver some 30 percent more power.

Sabre purchases the units from Volvo Penta “from steering wheel to propeller,” according to Collins — meaning the controls, helm pump, display screens, key switches and joystick, right back to the engines, transmissions, and propellers.

Every owner I spoke with crowed about the efficiency, the lack of vibration, and the exceptional maneuverability offered by pods. I initially chalked this up to a lack of time on the market; their problems would appear over time.

The fact that Volvo Penta propellers face forward makes them seem vulnerable to debris in the water. Surely that would be a negative, I thought. Indeed, a number of people who don’t own Volvo Penta systems on their vessels said this fact made them nervous, especially at the prospect of navigating a vessel in waters rife with lobsters, crab, or fishing gear. But no one I spoke with had an actual story describing a problem associated with this fact.

I asked Don Kohlmann, sales manager of PAE in Seattle, which builds sturdy oceangoing Nordhavn yachts, whether they considered pods for their vessels. Kohlmann cited concerns about floating debris on the Pacific. Anyone who has ever navigated in the Pacific Northwest knows that the sight of enormous logs — some 50 feet long and three or four feet in diameter — is not uncommon.

“Most of our boats are single-engine configuration with a wing engine. I think that the pods are more suited to twins with the joystick system,” Kohlmann said. “We are trying hard to protect the prop and the rudder from strikes, but also things like fish nets. When we do fit a boat with twins, each shaft has a skeg to support it and its rudder.”

Nordhavns are a completely different beast from Sabres, designed to be more ship-like and steam at stately speeds rather than coastal jaunts on a plane at 30 knots. (In fact, Nordhavn brags of its vessels’ engines turning propellers “slowly, quietly and efficiently” in its sales literature.)

Bob Gerwig, the mechanical foreman at Brewer Marine in South Freeport, Maine, has serviced pod systems since they came on the market more than five years ago. A taciturn New Englander, I thought he’d give me the straight scoop on pods. Unbidden, he, too, launched into a description of their benefits.

“These things have been on the market a while; they’re not brand new, so I think we would have seen problems by now. They stick down in the water so they’re a direct shot; it’s pretty efficient,” Gerwig told me. “Conventional drive is at an angle, so its not the most appropriate way to push a boat around. These stick straight down and they swivel — jeepers, they can do just about anything!”

The only potential negative, Gerwig allowed, was that replacing the artificial anodes in the propulsion system requires greater vigilance. “With the IPS drives, if you don’t replace the anodes every year, electrolysis starts eating into the drive housing itself,” Gerwig said. One vessel he worked on had been neglected in this way since the owner was not aware of this requirement.

“The corrosion on the drives hadn’t gone too far, but if he hadn’t replaced the anodes soon the corrosion would have compromised the whole system, and water would get in where the oil is,” Gerwig said. “Otherwise, the system is very rugged — bulletproof — especially since it’s coupled with the latest diesel engine technology.”

As with any boat, regular maintenance is the key to success. “The only difference is there’s way more money invested in pods than conventional drive systems if something does go wrong. A big investment like that doesn’t take care of itself,” Gerwig added. Gerwig had not seen any pod systems damaged by contact with fishing gear or other submerged objects.     
Harris, owner of the Sabre 54, said he recently installed serrated blades on his system out of a fear of snagging crab pots on the Chesapeake. So far, the system has worked, he said, or he’s been adroit at avoiding fishing gear.

Gerwig of Brewer’s Marine said that in theory there would be no worse problems associated with snagging lobster pots on a pod than on a conventional-drive propeller. “And most of the pod owners I know are pretty careful anyway. They have a big chunk of change hanging down there under the boat.”

Pods are designed to break away when they come in contact with a solid object at high speed, thereby preventing a catastrophic breach of the hull. Collins told me that this would happen only at a high rate of speed. “You’d have to be going flat out for this to happen,” he said.

Needless to say, Collins could cite no reason not to have a pod system, provided cost was not an issue. “The whole subject of spousal communication is a big one, and the strain on people’s marriages from docking maneuvers is legendary,” he said. “With pods, that anxiety is gone.”

Cost is an issue with pods, of course, but everyone I spoke with felt that this technology will trickle down to the rest of the industry before too long as more units are purchased and the industry recovers its investment in the new equipment.

“Overall it’s a pretty good system,” Gerwig said. “It’s here to stay, at least on the higher-end boat. We’ll always have inboard drives because they’re cheaper — cheaper to buy and maintain. For people who want the joystick feature, though, it’s the cat’s meow.”
        
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Twain Braden is a maritime law attorney and professional boat captain based in Portland, Maine.

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