A chain of efficiency gain

Vessel efficiency improvement is speeding up. Reduction of emissions is now one of the prime objectives in maritime engineering, leading to numerous innovations in ship propulsion that all help minimising fuel consumption. A quick round-up of recent Dutch initiatives and new technologies reveals green possibilities for ship owners in all sectors of shipping.

Naval architects and suppliers who overview the wide range of possibilities to optimise the propulsion on a seagoing or inland vessel, realise it may be hard to make the right decisions at the start of a project. Alterations in the engine room and propulsion train may prove effective on one type of ship with its specific operational profile, while the fuel saving effects of another vessel may turn out to not to have any positive effects given the different work loads aboard another ship. As the possibilities are numerous and piling up, it becomes harder to make the right choices at the very beginning of the design process of a new ship. Ship owners who need to reduce the carbon footprint of their operations can choose to install LNG powered engines or diesel-electric hybrid power plants in a number of variations. Hull form optimisation is also a possibility, just as alternatives for propeller propulsion are presented as potential big fuel savers. Both the O-foil and Whale Tail propulsion systems claim to achieve fuel savings of 30% and up. Hull forms of seagoing vessels gain efficiency with the ConoDuctTail, which allows ships to be operated with 20% less power installed, saving roughly the same percentage on fuel consumption. Another aspect of efficiency is monitoring the loads on the propulsion train, exactly knowing when service is needed, minimising maintenance and repair cost as well as reducing friction of worn mechanical components – saving both cost and energy.

Sales tool

It all starts with design. ”The customers of naval architects and shipyards typically present the outlines of the ship they want to build as a starting point for design”, senior sales manager maritime & offshore Dan Veen of knowledge centre TNO describes the process of creating a new vessel. ”In this phase of pre-order design briefs, it is often hard to predict which engine room arrangement and which propulsion train would be most efficient. That is why a number of suppliers, knowledge centres and authorities are participating in the ‘Hybrid III’ joint industry project. In this project, we are developing a calculation tool that can determine the most efficient set-up of propulsion in a very early stage of the design process. We actually intend to present it as a sales tool for naval architects and yards, a computer simulation programme that can quickly present fuel consumption and the need for power installed in different propulsion concepts.”

Optimisation of propulsion trains and hull forms follows decisions that need to be made in an early stage of the design process. At the point in the conceiving of a vessel in which propulsion optimisation can be done, a lot of development and design work is done with the preliminary chosen engine room configuration. At that point, deciding to start all over because another propulsion lay-out may prove more efficient will cost a lot of effort and money. Therefore, having a reliable tool that determines the right propulsion at a very early stage is the most effective way towards fuel efficient low-emission ship operation.

”We have some ten types of configuration in mind, from which the programme can choose”, Veen reveals in the early stage of the Hybrid III project. ”This will include conventional direct drive diesel propulsion, and different hybrid set-ups, like parallel hybrid propulsion or diesel-electric propulsion, both with or without added battery capacity. Also LNG-powered engines will be part of the possible outcomes.” Of course, the engines powering the hybrid propulsion systems can be LNG engines as well. ”Every ship has its own specific operational profile. Dredging vessels require strong engines to perform their dredging tasks but have different demands regarding propulsion power to get to their destinations. Coastal cargo vessels, however, have very limited varying loads as they navigate over seas. Inland vessels may navigate upstream and downstream, also resulting in very different power demands. Tugs are most extreme: in many cases they use full power less than 2% of their sailing time and sometimes have an average engine load of 20%. A lot can be gained here. The ship owner is the one who knows about this operational profile.”

Parties involved in the project are system integrators Imtech, Alewijnse and Croon, the Royal Netherlands Navy, naval architects Conoship, engine supplier and installer Bakker/ PON, Damen Shipyards, Antwerpen Port Authority and knowledge institutes TU Delft and TNO. CMTI will coordinate and about four or five extra participants are in the process ofjoining the project. Veen: ”Following the outcome of the Hybrid III project, a calculated decision for one specific propulsion system can be made, right at the beginning of the design process. We are convinced this will result in more efficient ships.”

Maintenance predictor

Choosing the right propulsion lay-out is one way to achieve low-emission ship handling. Maintaining the propulsion trains installed in tiptop shape is a way to be sure no energy is wasted as a result of wear at mechanical parts or thrusters working at inefficient loads. That is why Wartsila developed PCMS: the Propulsion Condition Monitoring Service. ”Initially, we developed this as a service product”, general manager Luc Dankers of the propulsion solutions department reveals. ”We recognised the need with ship owners to prevent malfunctioning of thrusters, so we developed a system that monitors the loads and vibrations of thrusters. The result is an insight in the condition of bearings and seals, which allows for maintenance just-in-time.” PCMS consists of a series of strategically positioned vibration sensors, attached to thrusters of large vessels that are equipped with dynamic positioning, or even on the thrusters of vessels that use them as main propulsion. These sensors measure the levels of vibration and the frequencies. Together with data about the thruster load during operation, with according rotations per minute and torque, the data from the sensors are automatically registered in a computer application that calculates the amount of wear the mechanical parts have been suffering. ”We know the diameter and the number of balls inside any bearing,” Dankers explains, ”so we know what the frequency of vibrations should be at a certain rotation speed. If this predictable vibration starts showing disturbances, we know something inside the mechanical train of propulsion is up for maintenance and also know which part, because of the frequency. The software clearly indicates the elements of the drive train that need looking after.”

Thrusters for dynamic positioning have very demanding, constantly changing loads, sensitive mechanical parts are underwater and are difficult to be serviced. Yet, overhauling the thrusters during dock times of offshore vessels is expensive and often takes too much time. Thruster overhaul takes longer than the maintenance of the working equipment and PCMS allows to determine which parts need to be serviced and does this within the narrow timeslot of a docking.

Optimising water flow along propellers is another way in which Wartsila helps making propulsion more efficient. ”For the large propellers of bulk carriers, tankers and container ships, large ones measuring seven to nine metres diameter, we developed the EPF”, Dankers says. ”The EnergoProFin is placed at the head in the middle of the propeller to transform the turbulence abaft the propeller into driving force.” Dankers shows the 3D-model of a ship propeller with an EPF added, as it was printed in plastic with Wartisa’s 3D-printer. ‘‘The concept of the added propeller in the middle of the bigger one is not new. With EPF, we have improved the concept. We expect to achieve from 2% up to 5% improvement of propeller efficiency, much better than added centre propellers did before. The number of blades, their position in respect to the bigger blades and the pitch are crucial for the efficiency.”

Water flow

‘If a ship’s hull has less drag in the water, less energy will be needed to propel the ship’, a simple argument that naval architects at Conoship followed. However simple the motto, the task is hard after 4,000 years of shipping to improve on the hull forms evolved. Still, this is what Conoship has achieved with both the ConoSeaBow and the ConoDuctTail. The special bow combines the calm water resistance reduction as achieved by a bulbous bow section, with the resistance reduction of sharp entry bows in a seaway. The stern section of the ship however, determines the way water flows towards the propeller and the way it is pushed into a wake field behind the stern. The ConoDuctTail combines advantages of different types of stern sections. The Pram type stern section has low drag in calm waters, but results in slamming in a seaway and loss of thrust. The moderate Pram type stern section with stern bulb shows even better efficiency. Tunnel shaped stern sections are designed to lead the flow of water towards the propeller and allow for the use of bigger, more efficient propellers. Tunnel shaped sterns have good sea keeping in rough conditions, but their drag is higher in calm waters as compared to Pram type sterns.

The ConoDuctTail has moderate tunnels in the stern section, so a large propeller can be applied. It maximises waterline length, to increase buoyancy and reduce the need for additional ballasting and makes use of a nozzle to further optimise the propeller’s thrust. Four sea-river vessels for operator Wijnne Barends, navigating coastal waters, canals and rivers, have been built with the ConoDuctTail. They need about 20% less installed power to achieve the same performance as comparable conventional hulls. Following the first years of sailing, fuel savings of over 10% are continuously achieved.

Fish tails

Noteworthy developments for the propulsion of inland water vessels are both the O-foil Wing propulsion and Walvisstaart (Whale Tail). Referring to the way a dolphin speeds through the water, O-foil founder Bas Goris explains the driving force of the profiled flaps, moving up and down through the water over the whole width of the aft ship. In February this year, the first inland ship was equipped with Wing Propulsion and the results were promising. Goris claims his propulsion system can result in 50% less fuel consumption. That is still hard to believe, but the Wing Propulsion is certainly available as a fuel saving option for the visionary inland skipper.

Another advanced project is the Whale Tale propulsion, basically two small type cycloidal propulsors under the stern section of an inland vessel. Apart from this main propelling system, the inventors are working on a steerable thruster, consisting of a rudder with cycloidal thrusters placed horizontally on both sides. Whale Tale is part of the European STREAMLINE project, which stands for Strategic Research for Innovative Marine Propulsion Concepts. In this project, guided by Rolls Royce Power Engineering, 22 partners from Western Europe work together on daring new ideas for moving through water.

Hans Buitelaar