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    Categories: FeaturesPowerLines

Pushing the Propulsion Envelope

By Mike Milne

New engines usually hog the spotlight in new recreational power boat developments. There have been plenty of important and note-worthy advancements in marine powerplants during the past couple of decades, but new modes of propulsion – working hand-in-glove with the engines themselves – have also made massive contributions towards keeping the pleasure in pleasure-boating.

For most boaters, how the power is delivered is as important as the power itself.

Arguably, little has changed substantially in shaft-drive or even V-drive inboard propulsion. Finding the right propeller for a given boat and engine remains a science bordering on art. The biggest changes in recent years have come in departures from traditional inboard propulsion.

The development of recreational inboard pod-drives – combined with onboard computer-driven digital technology and drive-by-wire engine and drive controls –has been revolutionary for inboard-powered medium to large cruising boats. Even a yacht with twin counter-rotating engines and a bow-thruster, all controlled by a skilled captain, are no match for the kind of manoeuvrability offered by computer-driven, digitally connected joystick-operated pod drives. Regardless of skill, a captain with joystick controls has much more command over the boat’s movement through the water at docking speeds.

Volvo Penta was first out of the gate with pod-drives when it introduced its  forward-facing twin-prop Inboard Performance System (IPS) drives in 2006. First developed for medium- to large-size diesel-powered cruisers, it has been used in a wide range of twin-, triple- and quadruple-engine installations.

As well as improving close-quarters handling, IPS pod drives also provide better fuel efficiency, faster planing and overall improved handling.

Volvo Penta’s joystick controls on the helm set-up of an Azimut 55S

My first hands-on experience with IPS was aboard a 42-foot Regal express cruiser. I moved it in and out of its place on a crowded dock by using the joystick to manoeuvre the boat parallel to the dock. The usual spring line and backing were not needed.

With one fell swoop, digitally connected joystick controls have addressed the skills gap that often kept wary, inexperienced skippers from moving comfortably into bigger yachts.

Mercury Marine was not long following suit with its rear-facing Zeus inboard pod drive system, complete with joystick controls. PowerBoat TV host and boat tester Mike Gridley says he has found Mercury’s Zeus system is at its best during slow-speed docking manoeuvres. While the IPS joystick system often delivers bursts of power when called on at slow speeds, “The Zeus drive system provides a much more progressive, linear, forgiving motion, especially when you are making that last little move toward the dock.” Instead of moving toward the dock too quickly, he says, there’s a more gradual motion.

Gridley says his most recent experience, driving a Sea Ray L590 Fly with triple Zeus pods, was impressive. “You could dock it anywhere you wanted. But on the water, when you poured the power to it, off it went with almost no bow rise.”

Not to be left out, other diesel engine builders also moved to joystick control systems, both with and without sterndrive or pod-drive technology.

Cummins joystick

Yanmar offers joystick control sterndrives through its VCS or Vessel Control System. Well-known marine diesel manufacturer Cummins – which worked in a joint-venture partnership with Mercury Marine for about 10 years – still offers engines linked to Zeus pod drives, as well as ZF and Glendinning units. Cummins also recently announced its Inboard Joystick Docking system, to electronically tie together engine controls on otherwise traditional shaft-driven inboards equipped with bow- or stern-thrusters.

Caterpillar Three60 precision control joystick

Caterpillar has a similar system that links traditional inboard installations with bow- or stern-thrusters. It’s called the Caterpillar Three60 propulsion system and claims the same 360-degree manoeuvrability as pod-based joystick systems. At the same time, Caterpillar has also teamed up with a Fiat Drive Train unit to produce the Cat Three60 Pod650 pod drive, putting it into more direct competition with the Volvo Penta and MerCruiser systems.

As well as making close-quarters manoeuvring more fun than feared, joystick control systems can also link to GPS to allow effortless station-holding – valuable if you’re waiting for a bridge to open, for example, in windy, high-current conditions. Mercury calls that feature Skyhook. The joystick systems also switch back and forth easily to let skippers use more traditional controls.

Sterndrives are also getting in on joystick action. Volvo Penta has extended joystick driving technology first introduced through the IPS pod drives to its DuoProp sterndrives. Mercury has also moved quickly to apply joystick technology to MerCruiser sterndrives, with its Axius joystick control system. Introduced soon after Zeus, Axius made joystick controls available on twin MerCruiser sterndrive installations with twin-prop Bravo Three drives.

The biggest sterndrive propulsion news from Volvo Penta, though, is the introduction last year of its new Forward Drive. Volvo Penta was the first sterndrive builder to come up with an inboard-outboard drive leg with twin counter-rotating propellers, when it introduced the DuoProp in 1982. In a way, the Forward Drive is a kind of melding of DuoProp and IPS technology.

Taking direct aim at the large and growing inboard watersports tow boat market, the Forward Drive offers some of the advantages of a sterndrive. But instead of fully exposed props mounted on the aft of the drive leg and pushing the boat, the Forward Drive has front-facing props on the front of the drive leg pulling the boat forward, IPS-style. The forward-facing props make Forward Drive equipped boats somewhat safer and more appropriate for wake surfing, now largely limited to inboards.

So far, Mercury has not come up with a sterndrive-style alternative to Volvo Penta’s Forward Drive.

On the outboard side, there have been few real revolutionary developments in recent decades. Outboard lower units designed for racing and high-speed operation have been streamlined, with low water-pickups for cooling at high speeds – and there have been improvements in strength, serviceability and convenience. Suzuki, for example, introduced Suzuki Select that allows counter-rotation at the flip of a switch in high-power outboards, but overall nothing groundbreaking.

In recent years, most outboard builders have built engines aimed specifically at the fast-growing pontoon boat market, with high-thrust gear ratios and beefier lower units to handle bigger props and higher torque needed by some pontoons. Mercury has its BigFoot outboards, Suzuki has High Energy Rotation and Yamaha builds High Thrust engines geared for pontoon propulsion.

As with sterndrives, outboards have benefited from the digital technology that allows joystick controls. With the spread of drive-by-wire controls, joystick systems are also now available with most high-power outboard engines. That means boats with twin, triple or even quad outboards on the transom can also opt for easier close-quarters handling that comes with joystick controls.

 

Yamaha Helm Master Controls

Mercury has extended its Axius technology to include outboards, while Yamaha offers the Helm Master system (based on Volvo Penta’s Electronic Vessel Control technology) for joystick controls for high-power outboards in multiple installations. The Suzuki Precision Maneuvering joystick system is available on 150-300-hp outboards that are equipped with the drive-by-wire Suzuki Precision control system. BRP’s new high-horsepower Evinrude G2 outboards are available with the I-Dock joystick system.

Water-jet propulsion, like outboards and sterndrives, has seen evolutionary rather than revolutionary changes in recent years. Low-speed handling with jet boats and PWCs has always been problematic because of the difficulty of creating a true neutral gear. That’s because the source of thrust – the water pushed out by an inboard impeller – is never entirely cut off. Neutral and reverse are simply created by changing the position of the bucket that redirects the water from the jet drive nozzle to make the boat move backwards.

Experienced PWC drivers know how to “find” a neutral position between forward and reverse, but recent digitally controlled systems on BRP and Yamaha jet drive systems do a better job of finding that sweet spot. Still, because a lack of water-jet thrust also means a lack of directional control, improvements in control usually need mechanical and digital elements.

Yamaha’s Advanced Responsive Handling system, for example, uses an Articulating Keel (much like a rudder found in traditional inboards) for added control at low speeds and improved handling at all speeds. There’s also a Thrust Direction Enhancer that re-directs water to provide optimum thrust and handling at various speeds. Combined with the keel, the system provides great improvements in low-speed handling that’s noticeable across the Yamaha jet boat line.

“With the new Yamaha jet propulsion system, you can turn it and spin it around easily,” says PowerBoat TV co-host Steve Bull, who recently tested a Yamaha 242 SE sport boat. The new propulsion setup, he says, “adds a lot of confidence and comfort around the dock.”

The Rotax water-jet units BRP provides to several boat-builders also benefit from electronic performance modes. The Rotax power packs now offer iST or Intelligent Steering and Throttle, which uses electronics to control what used to be mechanical functions. As well as providing electronic actuation of the reverse gates, the system lets drivers adjust the neutral position while under way. Along with BRP’s Lateral Thrust Control system, it is expected to solve the low-speed manoeuvrability challenge that comes with jet drives

Like other advances in propulsion technology, it bring boaters better performance, handling and more stress-free enjoyment.

This article is featured in the Summer 2016 issue of Boats&Places.

Mike Milne:

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