• Volvo seem unstoppable in their quest to keep on adding more and more functionality to their engine range.
  • What Volvo have ended up with … is a system that in my opinion no longer needs any sensors at all – it works brilliantly as it is, and in any berth.

Dave Marsh reports on Volvo’s latest initiatives in their ‘overarching goal of providing the whole of planet Earth with “easy boating”’ …

You could almost hear the furtive groans from the assembled journalists at Volvo’s annual press conference when the Swedish engineers finally did their big fanfare-of-trumpets reveal and announced that we’d travelled all the way to their famous Krossholmen test centre in Sweden to hear about a couple of updated engines and a new sterndrive. However, as it turned out, the company was being rather modest, and the updates were really radical engineering makeovers of the D4 and D6 ranges from the sump upwards, to the extent that we could almost consider them to be new engines. There was more that had also been significantly improved that PBR has written about in past issues, such as Assisted Docking, but not had the chance to test so thoroughly.

New DPI sterndrive leg

But first, the new DPI duo-prop sterndrive leg, which replaces Volvo’s DPH leg (although that will still be available for boats with all-hydraulic steering) and can be mated with the new D4 and D6 engine range. The big news here is the inclusion of a hydraulic clutch, which made the DPI such a joy to use in practice. Now, nudging in and out of gear is, to all intents and purposes, a silent affair ‒ so smooth that it’s only the usefully positive throttle detent and the fact that the boat moves that inform you that the engine is in gear. I used to avoid using the joystick to manoeuvre Volvo’s twin sterndrive-powered boats, because I always felt guilty about the relentless clunking of the mechanical clutches as they shuttled in and out of gear during the more complex manoeuvres. But now the hydraulic clutch has made this process a relatively serene one. We shouldn’t forget, though, that a sterndrive boat places the props much further back than the propellers in an IPS boat, and that means that the system is nowhere as effective or cooperative as it is with IPS, because the props have to work much harder to achieve the same ends. That’s not something that Volvo can change, it’s simply geometry at work.

Volvo’s engineers have utilised a higher-strength alloy for the duo-props, which means the blades can be thinner and (in theory) more efficient because of reduced drag. Currently, the duo-prop propeller sets that Volvo have designed can handle speeds up to 50 knots. That seems like a wasted opportunity, because there are plenty of high-speed RIBs, and other boats too, with which one would consider utilising a big single diesel instead of a pair of twin petrol outboards, because of the interrelated issues of fuel consumption, fuel tank size, fuel availability in remote places and range, which are particularly relevant for more intrepid long-distance cruising types.

Another benefit is that the steering is now electronic, with the final transfer to hydraulic (for the rams) happening at the last moment, typically near the transom. That makes for a far easier installation, eliminating the need for hydraulic pipes at the helm and allowing the builder to run a small flexible wire through the boat instead. It also allows Volvo to connect their electronic EVC features such as the DPS (Dynamic Positioning System), and Volvo’s autopilot will work with single sterndrives as well as twins.

Low-speed mode is another EVC function now available to DPI-equipped boats, adding the ability to dial the power right down by slipping the clutch. It’s brilliant for meandering slowly up rivers and inland waterways where, in a high-powered boat, in some places the speed limit is lower than the lowest speed available on tickover. With their inherently better directional stability, it’s less of an issue on a shaft drive boat whose skipper can simply knock one engine out of gear, whereas on a sterndrive boat I’ve always found that it’s nicer to be able to keep both engines pushing along at low speeds. Because the EVC also has a cruise control function, you can now effectively dial in the exact speed or power you want.

New D4 and D6 engines

Along with the engineering makeovers, the new D4 and D6 ranges have gained power, so in sterndrive form, top trumps now comprise a D4 320hp (up from 300hp) and a D6 440hp (up from 400hp). Both ranges have five wide-ranging power outputs: 150hp to 320hp for the D4, and 300hp to 440hp for the D6. However, the ratings for the inboard and IPS versions are staggered slightly differently ‒ most notably there is a new range-topping D6 480hp engine. That will please a lot of boatbuilders and designers who have been trying (overoptimistically, in my opinion) to push along ever longer and increasingly voluminous planing boats with the outgoing D6 435hp IPS package. Boats well over 50ft long and a hefty 20 tonnes fully loaded are not uncommon, with the consequence that top speeds have been steadily falling below the magic 30 knots. In truth, the problem is not so much absolute top speed but the fact that IPS-propelled boats are more sensitive than shaft drive powerboats to mid-season fouling or being overloaded or badly trimmed. So the 10% boost from 435hp to 480hp will be welcome, as will a much meatier torque curve, which will probably help heavily loaded cruisers even more.

So in engineering terms, what exactly is new? Among other things, the EVC engine management system, the cylinder head, pistons, valves and crankshaft, plus the common-rail fuel injection system, which now runs at 2000 bar, up from 1600 bar. The turbocharger and the supercharger are both new too. Owners of boats with lithium ion batteries will rejoice, because the new alternator can now charge their batteries and its output is a very healthy 150 amps, up from 115 amps. What has not changed one millimetre is the footprint of the engines. That’s significant because it will allow owners of very high-use boats to consider re-engining, knowing that the feet will sit in exactly the same place on the same bearers.

For the owner, though, given that the old D4 and D6 were already good solid engines, perhaps the more important news is the impact all this re-engineering has had on fuel consumption and the service side. Of course, without the luxury of extensive back-to-back tests in perfect conditions in otherwise identical boats, we can’t confirm Volvo’s claims of improved fuel consumption, which range from 0.5% to 7.0% (see graph) [SB1] and do not include the extra gains from the thinner propellers on the DPI sterndrive.

The data that Volvo supplied us with suggests that owners of new D4 and D6 engines should see a significant drop in servicing costs, largely as a result of Volvo dramatically reducing the number of service items, along with the labour hours needed to fettle the engines according to the service schedule down by 28%. Also, the volume of lubricants required has dropped by a third. It’s a similar story for the new DPI sterndrive leg, with its reduced spare parts inventory and labour down by 8%.

We had wild weather for the sea trials, with gusts of up to 40 knots, and lots of intrusive noise from the wind and the waves helping to unsettle our senses. So it was difficult to cross-reference back to previous experiences with the outgoing D4 and D6, and certainly impossible to get a feeling for the sound levels, either objectively or subjectively. When it comes to vibration and smooth running, the 6-cylinder D6 has always had the advantage of being far more naturally balanced than the 4-cylinder D4, and too many of the boats I’ve tested around the 30ft mark have been poorly insulated for sound and so have not helped the D4’s reputation for being a bit clattery. So the good news is that I would swear that the new D4 felt a little smoother than the old model.

Assisted Docking and DPS update

The eagle-eyed among you might spot that when we reported on Volvo’s newfangled docking thingamajig back in Issue 150, it was called ‘Self-Docking’. Now it’s called ‘Assisted Docking’. So what gives? Well, the original prototype system we wrote about used a combination of GPS and sensors on the dock to guide the boat into its berth. The big limitations of that approach are: firstly, you need to buy and install sensors on your dock; secondly, what happens if the marina master shuffles you around into another berth?; and thirdly, what about all those other docks you will be hoping to pull into on your travels?

Almost coincidentally, between now and then, Volvo enhanced their DPS by adding the ability to use the joystick to incrementally nudge the boat sideways or forwards or backwards by a fixed amount. Their engineers also added six cameras to the docking system ‒ cameras whose images can be individually viewed or knitted together to produce the sort of bird’s-eye view that you would get (see photo)[SB2] . That view is overlaid with a virtual bumper that’s set at a metre.

What Volvo have ended up with, perhaps by good fortune as much as wilful intent, is a system that in my opinion no longer needs any sensors at all – it works brilliantly as it is, and in any berth. The key is that at any stage of the docking manoeuvre, the DPS will not only hold the boat on station, it will also maintain a constant heading. So, as I discovered, all you need to do is approach your dock very slowly and carefully. If at any time you find your approach needs correcting ‒ a different angle perhaps, or a slightly different lateral or fore and aft position ‒ you simply let the DPS maintain your position and gently nudge or twist the boat into the perfect position using the joystick. You simply keep repeating that process until you are in the right position to step ashore. And with the DPS engaged, that could be on your own, with no crew to help.

There are two caveats. Firstly, the effectiveness of the system relies on the stability of the GPS signal that Volvo’s DPS uses to maintain the boat’s position and its heading, and that is not always a given. I once had a geostationary positioning system shuttle my test boat a very precise 3 metres backward and forwards up and down the dock ‒ exactly the distance I then realised was showing up on the fluctuating satnav readings. Secondly, as I discovered, in the sort of wild and windy conditions we experienced, the very sort where you might be most in need of a helping hand with the docking, especially in a tight berth, the combination of Volvo’s DPS and the IPS drives is not quick-witted or precise enough to maintain an absolute rock-solid position and heading ‒ a DPS-enabled boat will still shuffle around a little, depending on its aspect to the fluctuating wind and waves, before it settles again where it should. And that limitation would be more pronounced on a DPS-equipped sterndrive boat.

Volvo are not without their rivals. Raymarine’s assisted-docking technology, DockSense, uses a bumper that actually stops the boat from bumping into solid objects (as long as they register on the cameras), whereas on Volvo’s system, the 1m bumper is just a visual guide, not a force field. Each system has its advantages, but what I most like about the Volvo system is that it allows the skipper to ignore things that might hinder the docking process ‒ for example, the fenders you invariably encounter when you reverse into a typical stern-to Med marina berth, which are likely to be a centimetre away, not a metre.


Volvo seem unstoppable in their quest to keep on adding more and more functionality to their engine range. Quite what they will dream up next is anybody’s guess, but their overarching goal of providing the whole of planet Earth with ‘easy boating’ does seem to be getting closer. It will be interesting to see where they go with Assisted Docking. Currently, it is still work in progress and not commercially available. I hope that changes soon, because I reckon that even without further development, it’s a terrific system.

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