Shipping forecast

When the Royal Navy launched Daring, the first of its new Type 45 Class destroyers, last February, it was inevitable that much attention would focus on its integrated electric propulsion system.

This was a first for a front-line warship, giving Daringbig benefits in areas such as range and operational capability.

But while the ship was a landmark for the Royal Navy, the military’s maritime cousins in the commercial shipping sector could be forgiven for wondering what all the fuss was about.

In the commercial arena, truly ‘all-electric’ vessels have become ubiquitous, and while Daring marks a big step down the road, the ‘all-electric’ warship remains elusive to the world’s navies.

To merit that description, for example, systems such as the rudder and stabilisers would have to be operated by electric actuator instead of the conventional hydraulic systems. This is still a way off in the military sphere, with many challenges to overcome.

It is a different story in the commercial shipbuilding sector, where the move towards the all-electric ship began. Here, different degrees of electric ship technology have spread across most classes of new vessel, from cruise liner to ultra large cruise carriers, pleasure boats and private yachts.

One example is the world’s largest cruise ship, The Liberty of the Seas (see Insight). Launched last month, this huge vessel is driven by giant 16MW electric motors.

The success of all-electric ship technology in cruise liners and large yachts has shown that electric ships provide significant advantages in speed, manoeuvrability and hull-space use. But all of these have not, as yet, been successfully transferred to waships such as Daring, and in an unusual role-reversal, the military finds itself playing catch-up with its commercial cousins.

Despite this the system on Daring will bring big advantages to the new warship, including greater range and operability, and reduced maintenance, and hence the vessel’s through-life cost.

The system replaces the traditional, heavily-engineered shaft line, gearboxes and diesel engines. It not only turns the vessel’s propellers but supplies all the other auxiliary electrical loads aboard, in a fully integrated and managed system.

Generally, the modern electric propulsion system consists of a centralised generating system, which also supplies services requirements, and a variable speed drive system connected to fixed pitch propellers.

A comprehensive power management system ensures that each prime mover operates at its optimal load, while systems such as direct torque control of the motors allow immediate and smooth drive control with minimum wear and tear on the system.

Advantages of the technology over traditional propulsion systems include better safety and reliability, improved manoeuvrability, greater efficiency and enhanced passenger and crew comfort through reduced noise and vibration levels.

The concept also allows for the optimisation of a vessel’s architecture, so that priority can be given to other requirements, with the new components of propulsion, (prime movers, transformers and converters sited conveniently around the ship).

Most radically, ABB’s Azipod electric motors are placed outside the hull in a pod that can rotate through 360º. This has released space and offered better manoeuvrability.

ABB has also developed variants such as the compact Azipod for smaller vessels and the contra-rotating Azipod. The CRP Azipod is installed in place of a normal rudder, downstream of the main propeller that is turning in the opposite direction. This obviates the need for the large, hydraulic rudder system.

ABB says this configuration is highly efficient because the pod’s propeller uses the remaining energy from the rotating water leaving the forward propeller.

According to ABB the system encompasses unique advantages, resulting in the best hydrodynamic efficiency in the industry. Gains in efficiency are achieved by applying the CRP principle, dividing the load over two propellers.