Gas turbines and generator systems for yachts

2015-01-21By Dag Pike
The 118 WallyPower uses three turbines to give a top speed close to 70 knots

Gas turbines offer the most concentrated source of power in the marine world. With a turbine it is possible to pack 5,000hp into the same space that would be occupied by a 500hp diesel engine.

They are very light in weight for the power they produce; their maintenance requirements are much lower than a diesel engine because they just have one or two moving parts; they don’t need a vulnerable cooling water system; and they can produce full power immediately from start up.

Navies of the world love them, so why are gas turbines still seen as an exotic power source for motor yachts?

Cost of gas

The main answer is cost. A turbine will cost perhaps four times as much as comparable diesel power. Their fuel consumption also is higher than a diesel and tends to remain high even at intermediate speeds.

As far as motor yachts are concerned, gas turbines are generally used as a way to boost power rather than as the main means of propulsion. In this role they will be found installed with a pair of diesel engines, with each engine coupled to a water jet. The wing diesels provide the normal cruising power, perhaps taking the speed up to 35 knots, then the turbine can be switched in on the centreline jet, perhaps adding another 10 or 15 knots to the top speed.

Gas turbines are generally used as a way to boost power rather than as the main means of propulsion

This is the engine package offered on the Pershing 115, where an owner can choose between having just a pair of MTU diesels producing around 5,500hp for speeds of around 35 knots, having three of these diesels, or replacing the centre diesel with a 5,000hp gas turbine that will provide a top speed close to 50 knots.

Danish Yachts offers a similar package on its very lightweight 38m Aerocruiser, where the addition of a 5,000hp turbine can take the speed to over 60 knots.

The favoured turbine for these applications is the TF50 from Vericor, which is a tried and tested unit that comes in two other versions: the TF40, and the new TF60. The same turbine unit can be configured to produce various power outputs. These units are the most popular in the yacht sector.

The high-performance 118 WallyPower used three TF50s for main propulsion – one of the few all-turbine installations on a motor yacht. The high speed of the basic turbine of around 20,000rpm had to be geared down considerably to match the requirements of the water jet units, typically to around 1,000rpm. There are specialised lightweight gearboxes to meet this requirement.

With all three turbines in operation, the _118 r_eached speeds close to 70 knots. For harbour manoeuvring, the turbines were a bit fierce, so a pair of 500hp Cummins diesels could be coupled into the wing water jets for more gentle progress.

The 86m Ecstasea uses a turbine as a booster

The Aga Khan’s gas-powered yachts

While the 118 was a complex installation, but even more complex was a yacht built under considerable secrecy at Devonport Dockyard. Reportedly built for HH the Aga Khan, this 42m yacht was powered by no fewer than six gas turbines coupled in pairs to three water jets. The smaller turbines were thought to be Eurodyne units, each producing about 3,000hp.

The smaller turbines were for relatively low speed cruising and harbour manoeuvring. When high performance was required, the second batch of turbines – each delivering around 10,000hp – could be coupled in. The yacht was designed for speeds of up to 80 knots, and the result was one of the most complex machinery installations ever. She was plagued by considerable delays mainly caused by the machinery and its final speed potential has never been revealed.

When high performance was required, HH the Aga Khan’s yacht could use a second batch of turbines – each delivering around 10,000hp

HH the Aga Khan was no stranger to high performance, with his involvement in the Destriero project, a 67m vessel built to challenge for the trans-Atlantic record. Powered by three General Electric LM1600 gas turbines, she had around 52,000hp on the throttles and averaged 53 knots across the Atlantic, burning fuel at the rate of 10 tonnes per hour.

On board the 86m Estasea, built for Roman Abramovich, there was one General Electric LM2500 gas turbine. This turbine produced around 30,000hp and was supplemented by four MTU diesels totalling over 12,000hp.

The diesels allow a variety of flexible cruising speeds and when the turbine is coupled in the speed could reach 28 knots – fast for a superyacht of this size – although the fuel consumption obviously shoots up resulting in a drastically reduced range.

Gas turbines are at the exotic end of the fast motor yacht market, but they continue to attract attention from owners and builders who want a vessel that will stand out from the crowd. When money is no object, the gas turbine can still be an attractive power source for propulsion systems.

However, the possibility of using gas turbines to power a superyacht’s other electrical systems is now being explored.

The internals of a gas turbine. Once the preserve of high-performance yachts, they may find a more general use as generators

Gas turbine generators

A pioneering installation on board an inland waterways tanker operating on the River Rhine is showing how gas turbines can be used as efficient and clean electricity generators.

This 110m barge has two gas turbine-powered generators that not only supply the vessel’s electrical power, but also can provide the domestic hot water, heating and air-conditioning – and they do this while generating very low emissions that can exhaust without any treatment to meet stringent regulations.

It opens the door to a new generator concept for superyachts and Pon Power of Holland, who developed the system, is keen to explore this market sector.

The barge’s system uses a pair of US-built Capstone C30 30kW gas turbines coupled to the vessel’s generators. They not only provide the electrical power, but the hot exhaust gases are passed through a heat exchanger, which in turn provides the hot water for domestic use and heating. Part of this exhaust heat is also fed to an absorption chiller for the air conditioning, making the most of energy that would normally be lost.

The exhaust from the turbine shows a significant reduction in harmful emissions compared with a normal diesel, and smooth running and low noise levels improve the on-board environment, reducing the need for insulation.

The age of gas

This particular vessel uses natural gas for both main and auxiliary engines. The turbines operate very happily on this gas as well, but they also can be programmed to use most common fuels such as diesel and jet fuels, which makes them suitable for superyachts.

The exhaust from the turbine shows a significant reduction in harmful emissions compared with a normal diesel, and smooth running and low noise levels improve the on-board environment, reducing the need for insulation.

Capstone currently offers three models producing 30, 60 and 200KW, which would meet most generator requirements. They are used on many land-based applications and have been approved by Lloyd’s Register of Shipping. The turbines are equipped with special bearings that require no lubricating oil, eliminating another possible source of contamination.

There is obviously considerable potential for superyachts, particularly high-performance yachts, where the low weight and compact size of the units could create a performance bonus. The available sizes of the turbines should meet the auxiliary requirements of most yachts and the quiet and absence of vibration could lead to peaceful nights in the marina.

Originally published in Superyacht Owners’ Guide to Propulsion 2012.

Originally published: Superyacht Owners’ Guide to Propulsion 2012.

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