Big results. Minor changes.

Nowadays, a lot of research and projects involve the environment and sustainability. The workboat industry is no exception. Knowledge institute TNO, together with five market parties, investigated how the fuel consumption and emission of tug boats can be reduced.

In 2012 Voith Turbo took the initiative and approached TNO, to see if research could provide a way in which fuel could be saved in an already existing propulsion configuration. Project EcoTractor took off in 2013 and ended in 2015.

“A lot of research focusses on hybrid propulsion, LNG or other alternatives to save fuel. However, a lot of existing vessels are fitted with a diesel engine in combination with a propeller with controllable pitch. We noticed that a lot of companies were curious to see if you can achieve savings without making many changes to existing vessels”, says Edwin Bonsen, vice president marine EMEA at Voith.

Dan Veen, senior business developer at TNO, adds: “Vessels are built to fit a certain purpose, for example to ship a set number of containers. Tug boats are designed to be able to handle a certain bollard pull. However, no one ever checks if the vessels are doing the work they were designed for and/or is using all the power they were designed with. That is why we thought that perhaps, if you know the data about the actual performance of a vessel in combination with its original design profile, the vessel’s fuel consumption can be adapted to the actual user profile.”

Co-financed

Eventually, Voith, PON Power, Caterpillar Marine, TNO, Multraship and Novatug were gathered for the project, which is co-financed. “This means that TNO pays 85 per cent of the costs and the remaining 15 per cent is contributed by the companies. TNO receives a subsidy from the government, in order to enable companies to test ideas of which the outcome is uncertain. For commercial parties, it is hard financially to do research when it is unsure whether or not the end result is exploitable. This way, the cost threshold is lowered. And since TNO has no commercial interest, the results are used to assist the maritime industry”, explains Veen.

Collecting the data

“In order to test the performance of a Voith Schneider Propeller and a Caterpillar engine, we had to find a vessel which was fitted with both. Therefore, we contacted Multraship, whose tugs are fitted with both”, explains Bonsen. For the project, two types of Multratugs were put to the test, among which the Multratug 4. This is a tugboat with a 75 tonnes bollard pull, a Caterpillar engine and Voith Schneider Propeller. A team of students joined the crew of the tugboats to collect all the data of the vessels sailing performance. The data collected showed how much energy is put in each component of the vessels propulsion system and engine.

Veen: “These studies showed that the tugs spend most of their operational time sailing and being stand-by, although the setting of the engines and propulsion train are based on the design specifications which were pulling heavy loads.”

Optimised settings

Based on all the gathered information, TNO developed a simulation model, called GES, that is able to calculate the expected fuel consumption at different settings of the engines and propulsors. “So, now we could answer questions like what will happen when we adjust the engine settings, or when we adjust the ship’s screw or propeller”, says Veen.
This way, the vessel’s control strategy could be optimised leading to a reduction of fuel consumption. Next to the engine and the pitch of the propeller, the speed is an important factor when reducing the fuel consumption.

Veen continues: “We simulated a variation of situations and put together the optimum condition in which, according to the simulation model, nine per cent fuel could be saved. To reach this goal, we also had to calculate the most optimum speed. Sailing too slow or too fast could influence the fuel savings.”

Speed is important

“Emissions are automatically derived from fuel consumption. In the case of tugboats, this is an important issue since they mainly operate in ports and residential areas. Speed has a big influence on the emission levels of a vessel. That is why not only the settings of the propulsion systems were optimised, but the sailing profile as well. By simulating different situations in the GES-model, we can tell what the best sailing speed is and which emission levels this speed will cause. Our clients can benefit from this as well”, continues Bonsen.

The Multratug 4 was adjusted to these parameters. For each ship speed there is an optimum pitch of the propeller in combination with the rpm of the engine and the load of the engine. By changing the control strategy between engine and pitch of the propeller, in combination with desired thrust and sailing speed the vessel would perform at its optimum,meaning low fuel consumption and therefore lower emissions. Furthermore, the partners found that sailing at a low reps helped achieving their savings goal.

Damage control

But is sailing at a lower rpm not damaging the engine? “Sailing at lower rpm indeed is a bigger burden to the engine, and you do not want your fuel savings to lead to a damaged engine. Caterpillar therefore measured if the new settings did not exceed the recommended specification of the engine. Luckily, this was the case and no extra wear and tear should arise”, answers Veen.

The results

After trials, it turned out that the Multratug 4 could save 146,000 litres of fuel a year. “In the old situation, the vessel used the power it was equipped with two per cent of the time and was wasting fuel 98 per cent of its operational time. We found that if the vessel was sailing economically 98 per cent of the time, it is no problem when it is less sustainable during two per cent of the time when it is actually pulling. And the best part is, no major changes to your vessel are required, since you only need to adjust the settings of the existing equipment”, says Veen. “We are very happy with the results of the project”, adds Bonsen. “However, the success of the project is determined by the client’s satisfaction. Furthermore, we are going to use the results of this project in our daily works, amongst others in designs for new vessels but also to optimise the performance of new vessels.”

Successful sequel

After the success of the method has been proven with Multratug, another company has approached TNO for a change of settings. Flinter, a shipping company based in the Netherlands, was looking for a way to reduce their fuel consumption and emission, because of the stricter regulations around SECA-areas and their choice to sail on the more expensive low sulphur fuels. The type of vessel is a coaster, so its design purpose is different form the tugs. Veen: “When the coaster was designed they expected the vessel to sail 20 knots. We found that 16 knots is a more optimum speed. Last week, Flinter reported back that they have been able to safe ten per cent fuel.”

Anne Kregting