Volvo-Penta Drive pods are fitted to the crew transfer vessel Impresser, the first commercial boat fitted with the IPS PP system
Volvo-Penta released its original Inboard Performance System (IPS) pod drive with tremendous fanfare at a press junket in Gothenburg, Sweden in 2005. I was there. Marine journalists from all over the world were put behind the wheel in twelve IPS-powered boats. We ran them at high speeds in impressively tight turns through the rock-strewn channels and islands that line the thoroughfare into Gothenburg. We were blown away by the performance and maneuverability. Since then, Volvo-Penta has sold more than 40,000 of the propulsion units.
A few core features make the IPS particularly attractive to designers and builders:
- Ease of installation (essentially, the boatbuilder just needs to provide an appropriately sized and reinforced hole in the bottom of the boat).
- Dual, forward-facing, horizontally mounted, counter-rotating propellers that provide unbeatable efficiency.
- An articulating pod drive (including redundant steering motors) that eliminates the need for a rudder and conventional steering system.
- A bronze drive leg and rugged gear train that make the unit corrosion resistant and reliable.
- The software suite that provides joystick steering, sophisticated feedback in tight turns, and integrated trim control.
- A single supplier providing total vessel integration from the bridge to the propeller, with multiple helm stations easily installed.
In the 20 years since that release, Volvo-Penta has continuously upgraded IPS features, notably on the software and control side, with improved joystick docking (you can drive a boat in any direction, including directly sideways, and rotate it in its own length), and, more recently, the dynamic positioning system (DPS), which holds a boat in the same geographic location and alignment regardless of wind and tide.
When I received an invitation to return to Gothenburg this summer for the release of the IPS Professional Platform, and I saw photos of what looks like an enlarged version of the now very familiar IPS, I was inclined to give it a miss, but was intrigued by the insertion of the word “hybrid’ into the description. I shot off a couple of emails seeking further information and was told it was under wraps until the release. I confess I’m a bit of a sucker when teased with so-called ‘hybrid’ releases. I agreed to join them for the unveiling. Volvo-Penta flew me to Gothenburg. When the group of assembled journalists introduced themselves, I announced myself as a skeptic. Then we were introduced to the new IPS Professional Platform (IPS PP), which looks exactly like a giant IPS unit, but that’s where the comparison stops.
Nigel Calder Journalists crowd the bridge of a commercial ferry test boat during the propulsion system unveiling.
IPS Professional Platform
The new propulsion platform is designed for commercial vessels and superyachts from 82’ (25m) to about 180’ (55m) in length. The power unit for now (more on this in a moment) is the Volvo-Penta D13, which comes in power ratings from 515 kW (700 hp) to 735 kW (1,000 hp). This is an IMO Tier III compliant engine (IMO Tier III is similar to EPA Tier IV) with Volvo-Penta’s selective catalytic reduction (SCR) exhaust after-treatment equipment. With future carbon emissions reductions in mind, the D13 engines can be run on 100% hydrogenated vegetable oil (HVO) as well as conventional diesel fuel. Volvo-Penta is also actively involved in adapting its engines to methanol.
The D13 engines are designed for high torque at low rpm. Whereas the original IPS units are suitable only for planing hulls, the IPS PP can also be installed in displacement hulls. There is a fixed 2.9:1 gear ratio to achieve relatively low propeller shaft speeds. When put these elements together—commercial, rather than recreational service; high powered propulsion input optimized for low-speed torque; high gear ratio; displacement hulls; and Volvo-Penta’s counter-rotating propellers (there is a choice of 14 different propellers, depending on the application)—and you have a recipe for exceptionally high loads on the drive train. Especially when accelerating hard, the shaft can be subjected to as much as 120 kilo-Newtons (kN) of torque at the propeller shaft. Project manager Petter Audolf told me, “Every component in the drive is completely new. Nothing has been carried over from the old IPS.”
The hydraulically activated clutch in the IPS PP is adapted for low-speed maneuvering. At engine idle (600 rpm) the clutch can be slipped to the point that it reduces the propeller shaft speed by 90 percent down to ~20 rpm (the math is 600 rpm with a 2.9:1 reduction gear = 207 shaft rpm, which with 90% slip = 20.7 rpm).
The rotation of the IPS PP pod has been increased to +/- 40°. Compared to the more limited rotation of the original IPS, the new system enables joystick steering and docking and the DPS function without a bow thruster.
The power head on a traditional IPS unit has a single connected engine. The IPS PP is designed for two connected propulsion units, one on each side. Currently, these are two D13 engines, but shortly we will see a D13 on one side and an electric motor on the other side in a hybrid installation. The company promises that as battery technology and shoreside infrastructure mature to be commercially viable and reliable, two electric motors for fully electric propulsion can be connected.
The propulsion units are connected to the IPS PP gear train via a form of sprag clutch—essentially a ratcheting device that freewheels in one direction and locks in the other. This enables Volvo-Penta to optimize the performance and efficiency of these dual-propulsion unit systems (Volvo-Penta calls this the “Eco mode”). Engines and electric motors can be brought seamlessly on and offline when under way depending on power demands, governed by fuel maps, battery state of charge, and whatever other parameters the designer wants to include.
When under way powered by a single propulsion unit, adding the second one requires that it be started and accelerated. When its speed reaches that of the first unit, the clutch engages to bring both online. If one is slowed down below the operating speed, its clutch begins to freewheel, and the propulsion unit disengages. The transitions are smooth.
As with the original IPS, the exhaust for a diesel engine exits out the back of the IPS PP pod, reducing engine noise. If back pressure rises above a set level, a bypass opens to vent over the side of the vessel above the waterline. This system is designed such that when in pure electric propulsion mode, air can be pulled in and fed out the back of the drive leg to reduce drag.
Given that all IPS units are installed at least in pairs (and some as triples, and some quadruples) there is always built-in redundancy. With the IPS PP there are now a minimum of four propulsion units which can be mixed and matched for diesel and electric, and up to eight propulsion units in some installations for installed power levels from 2,000 kW to almost 6,000 kW. Electric motors will be up to 550 kW, each with two motor controllers (inverters) providing the input power from a nominal 750-VDC source fed by a lithium-ion battery pack. There are plans to provide electric power levels above 550 kW with quadruple inverters.
Real-world testing
How does this work in practice? Volvo-Penta conducted thousands of hours of computer simulations, based on its gigabytes of data collected over many years in numerous applications, before moving to real-world testing. To that end, the company acquired a 25-year-old, 123’ (37m), 400-ton, catamaran-style Norwegian ferry with a service speed of 31 knots. This ferry had been retrofit in 2018 with new engines connected to controllable pitch propellers (CPP)—an optimized version of a conventional inboard propulsion system. Volvo-Penta collected a lot of data based on a typical duty cycle for this type of vessel and then refit the ferry with an IPS PP installation in each hull, each with twin D13 engines (no electric so far). In that change, total installed power was reduced from 2,880 kW (3,860 hp) to 2,360 kW (3,200 hp), approximately a 20% reduction. The same set of tests was run.
The performance notes were as follows:
- Same top speed (32 knots).
- Time from zero to 32 knots reduced from 55 seconds to 28 seconds.
- Overall fuel savings of 22%, with much higher savings at low speeds.
- Considerably tighter turning circle.
- Substantially reduced engine run times because of the ability to shut down individual engines when not needed (based on the sample duty cycle used, the run time per engine is predicted to be reduced from 2,000 hours per year to 1,400 hours per year, which translates to considerably less maintenance and down time).
- The compact nature of an IPS PP installation as compared to the conventional installation freed up four meters of space in each hull (more could have been saved if the IPS PP had been built into the original design and weight calculations).
- The installed weight is two tons lighter.
First commercial application
Having validated the predicted performance, Volvo-Penta looked for a partner to conduct real-world testing. Northern Offshore Services (NOS), a company which specializes in servicing offshore wind generators (of which there are now thousands in the North Sea) stepped up to the plate.
Volvo-Penta Impresser under way will be able to opt for diesel or hybrid propulsion.
NOS has built a brand-new, state-of-the-art, crew transfer vessel (CTV) designed around the IPS PP, including future-looking features. The Impresser is a 113’ (34m), 384-ton, catamaran-style vessel with an IPS PP in each hull. Currently, all propulsion and energy generation for hotel loads is diesel-powered, although it will be a simple transition to hybrid and fully electric when those technologies become practical. In each hull the Impresser has a Volvo-Penta 112 kW, variable speed, DC generator feeding a 94 kWh lithium-ion battery pack. Inverters power the AC loads.
While the hotel load is only around 20 kW, NOS has fitted the large generators as it plans for a future when electric propulsion will be added to the IPS Professional system with each battery pack expanded to 1,128 kWh (for a total installed capacity of over 2 mWh). Much of the time these CTV vessels are standing by somewhere in a wind farm or are nudged up against a platform at the base of a wind generator and held in position by forward thrust. In both cases it will be possible to do this under electric propulsion powered by energy from the battery pack and the 112 kW generators keeping up if the batteries get low.
Nigel Calder Two out of 3 battery spaces on the Impressor; only the first in use for now.JPG (CAPTION: There is ample space for battery banks on the Impresser
In anticipation of the availability of high-speed battery charging directly from the wind generator towers in the future, Impresser already has the built-in ability to charge the future 2 mWh battery packs at an astonishing 2 mW rate from a 4,000V supply.
As with the Norwegian ferry, even in diesel-only propulsion the Impresser will deliver significant efficiency gains through the IPS PP installations and be ready to transition to hybrid and fully electric modes when these becomes practicable. However, this level of technology does not come cheap. One of the principals of NOS estimated the “future-looking” features added 20% to the build cost. This will not be recoverable in increased revenue generation until these features are realizable.
Philosophical foundation
The efficiency and other gains of the IPS PP system are worthwhile in and of themselves. In addition, Volvo-Penta is positioning itself to strive for net-zero carbon emissions necessary to combat global warming. This is not an easy task for an engine manufacturer whose entire business has been built on burning fossil fuels.
Volvo-Penta’s philosophy is summarized by Johan Inden, the Vice-President for marine: “There will be no binary shift: one day we run on diesel and the next we run on batteries. We believe the combustion engine will be here for a long time as we transition to all electric. But it will burn different fuels, and it will move through incremental phases towards all electric. We have positioned the IPS PP system to be forward-looking and adaptable to all these phases.”
The IPS PP is an impressive adaptation and renewal of the original IPS concept.
