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Marine Propulsion & Auxiliary Machinery

Marine Propulsion & Auxiliary Machinery

New markets drive demand for hybrid transmissions

Mon 11 Feb 2019 by Gavin Lipsith

New markets drive demand for hybrid transmissions
Additional power take-ins and an in-house electrical motor feature in ZF's hybrid transmission family

Hybrid and electric vessels are placing greater demands on gearboxes and transmissions as the use of power take-off and take-in becomes even more critical to flexible, efficient operations

With the emergence of hybrid and fully electric vessels, transmission specialists have been working to upgrade their equipment. While in many cases this can be as simple as adding extra power take-off or take-in capability, there are other ways in which gearbox supplies are adapting to these new market demands.

In January, Servogear started the assembly of two HDE220 hybrid gearboxes for the sightseeing and whale-watching vessel Brim Explorer. Sustainability is a key part of both the technical specification and the operator’s marketing message. The hybrid system will allow seamless integration of renewable energy into the vessel’s power system.

The energy-efficient and silent hybrid electric vessel is being built by Maritime Partner and is owned by Green Wave Holding. It will enter operation this summer. A battery capacity of 800 kWh will ensure silent and zero-emission propulsion in the most vulnerable areas, while a diesel-electric propulsion system will ensure engine power is to hand for longer-range sailing.

Servogear’s delivery comprises the HDE220 hybrid gearbox, a 1400 mm propeller, propeller tunnel, effect rudder, shaft bracket, battery package from Grenland Energy and energy management system from Brunvoll Mar-El. The hull is designed by Wave Propulsion, and the topside by Einar Hareide.

"Operating cruise vessels in vulnerable areas requires low noise and low emissions, which [can be] achieved with a hybrid gearbox"

“We see a new market emerging for smaller, lightweight cruise vessels,” says Servogear CEO Torleif Stokke. “Operating cruise vessels in vulnerable areas requires low noise and low emissions, which is what we achieve with the hybrid gearbox in combination with a custom-made propeller and tunnel.”

The market is evolving quickly, and equipment manufacturers are having to adapt again from diesel-electric to fully electric vessels. It was only last year that the lightweight carbon-fibre and fully electric cruise vessel Future of the Fjords was baptized by Norwegian prime minister Erna Solberg. The ship has already become a design icon, and its technical specifications have also received considerable attention.

A clean legacy

Servogear provided the propulsion system: propellers, shaft, shaft brackets, effect rudder and gearboxes. In December last year, the company was awarded a repeat contract for the next vessel in the series, Legacy of The Fjords. Another fully electric vessel, Legacy of the Fjords, will offer tourists and citizens of Oslo zero-emission voyages on the famous Oslofjord, in the most densely populated area in Norway.

Although sailing in the Norwegian fjords is becoming more environmentally demanding, fully electric voyages are not likely to become the industry norm soon. Transmission specialist ZF Friedrichshafen is therefore focusing its development efforts on the growth in hybrid propulsion. This does not exclude it from projects in Norway’s sensitive areas; the company supplied hybrid transmissions to the original Fjords vessel, Vision of the Fjords.

ZF sales manager Wolfram Frei describes the company’s decision to extend its hybrid transmissions portfolio as “the right move at the right time”. He argues that hybrid propulsion enables more vessels to tap into the fuel savings and environmental benefits that electric propulsion can afford.

“The required engine power in vessels is very high and as they travel very long distances, purely electrical-driven vessels will always be the minority,” he says.

At SMM Hamburg last year, the company revealed its complete line-up of hybrid-ready gearboxes, ranging from about 600 kW to a maximum of 10,000 kW. In the lower power range, the hybrid-capable transmissions can be combined with electric engines and inverters of between 150 kWe and 600 kWe. An example is ZF’s own CeTrax electric motor, with a maximum power of 300 kWe.

At the higher end of the power range, the ZF 8000 is suitable for engines with a power output of up to 3,000 kW. These models cover a wide field of applications, from coast-guard vessels and yachts to ferries, supply ships and small tankers. A compact, modular design saves on installation space and weight and also allows for a flexible installation in the ship’s hull, making retrofits easier. The ZF 8000 will be available as a parallel installation with a vertical offset.

"Traditional PTOs are constantly engaged, resulting in excess fuel consumption and wear on equipment"

The main difference between ZF’s conventional and hybrid transmissions is an additional power take-in (PTI), which exerts force on the propeller shaft via an electric motor either alone or in combination with the conventional engine. This additional drive can handle a large variety of gear ratios. An optional spur gear drive compensates for the speed differences between the main engine and the electric motor.

Since SMM, the supplier has delivered hybrid transmissions to vessels including ferries, yachts, tugs and patrol vessels, and has received further orders. Mr Frei notes that these applications are all for main diesel engines in the 1,000 kW to 4,000 kW power range.

Flexible arrangements

While the portfolio may be complete in power range, ZF will be working on further improvements to installation flexibility. It plans to introduce both ‘V’ and ‘A’ configurations – a reference to the angle of the output shaft and input shaft, which can result in important space savings in the length of an engineroom. In the case of the hybrid transmissions, this means that they can now occupy the same footprint as standard transmissions.

These new configurations highlight the flexibility of ZF’s gearboxes and will be particularly valued by yachtbuilders, says Mr Frei. “The decision between a standard or a hybrid propulsion system can be taken without any changes to the foundation,” he explains.

While power take-off, or take-in, is essential for hybrid propulsion, it can be used for several other applications – many of which do not need to be continuously powered. For example, fishing or offshore vessels can run deck equipment hydraulics from a propulsion shaft. But they will generally not require these to be powered while they are underway.

A new system from Finnish gearbox specialist Katsa allows shipowners to decouple devices run by power-take off without shutting down engines. The clutched, twin power take-off (PTO) gearbox is suited to vessels that use the PTO to run systems that are not always in use, such as pumps or hydraulic deck machinery. Traditional PTOs are constantly engaged, meaning they supply power to the devices or systems to which they are connected even when not being used, resulting in excess fuel consumption and wear on equipment.

Katsa sales manager Mikko Happonen says that the product was developed as a result of interest in the passenger and fishing segments. For fishing vessels, a PTO driving hydraulic systems would unnecessarily divert power from propulsion until deck machinery is needed.

The new gearbox is available for propulsion engines with a power output of 800 kW, a range that can include small workboats. It is designed to fit between the engine and the main propulsion gearbox. It can be retrofitted as well as installed on newbuild vessels, but would require layout changes to the engineroom due to the extra components between engine and gearbox.

Mr Happonen notes that Katsa is already considering similar solutions for outputs of up to 2,500 kW. This is a clear indication of the trend, noted by many suppliers, that hybrid powering is becoming a reality for ever-bigger vessels. Transmission technology will continue to evolve as the hybrid market develops.

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