Giving vessels fins to optimise fuel performance
An innovative technology by Norwegian company Wavefoil could see ships mimic the way whales move through water to cut fuel consumption and CO2 emissions.
A ship sailing through still water faces less resistance, and therefore consumes less fuel than one navigating a more turbulent environment. Waves that are similar in length to the hull of the ship amplify resistance due to resonance, resulting in large heave and pitch motions. “When vessels are faced with navigating such waters, their fuel consumption increase by about 40 to 50 per cent,” Michael Paulsen, sales engineer at Wavefoil, told journalists visiting the Norwegian University of Science and Technology (NTNU) last month. “You use more fuel, you pollute more and lose a lot of speed.”
One solution to this problem comes in the form of retractable wave foils, which dampen these motions to eliminate additional resistance. The idea stems back to the 19th Century when Canadian whalers observed the forward momentum whales have when their fins move up and down. They noted the smooth transition of the marine mammal through the water due to the way its fins operated. As a result, the idea of fins for ships came about.
“The idea is actually quite simple in itself,” said Mr Paulsen. The retractable bow fins are modular and installed in the bow of the ship, being partly or solely propelled by wave energy. As the vessel moves up and down with the waves, the foils generate a lift that delivers a greater forward thrust than the drag working against the forward momentum of the ship. This wave power is converted into propulsive power. One difference when it comes to ships is the location of the fins. “We install these on the front of the ship instead. It’s easier to install this way and the further forwards you have the module the greater effect you have.”
According to studies and trials conducted by Wavefoil, the technology has the potential to save thousands of Euros worth of fuel each year, as well as making significant contributions to the reduction of CO2 emissions. Pitch reduction of 30 per cent is also possible.
The first trial led by Wavefoil was on the Teistin vessel, a 45-metre ferry operated under the Strandfaraskip Landsins, the nationally owned transport company of the Faroe Islands. The vessel has been operating since September 25 with the retractable bow foils, taking passengers between Gamlarætt, Skopun and Hestur in the Faroe Islands with early feedback indicating problem-free transit. According to Teistin’s captain, “The ride in the waves is a lot smoother in every way.” Mr Paulsen noted that it is “too early to say anything about the reduction in fuel.”
In addition to this first installation, Havila Kystruten came onboard for a 6-month model experiment, which confirmed fuel reductions of 12 per cent and motion reductions of 10 per cent. According to Mr Paulsen, the company plans to install modules on four of its ships thanks to the simple technique and ease of operation.
Mr Paulsen also confirmed that Wavefoil has completed some calculations for installation of its largest available module to a Heritage Expeditions 130m explorer vessel. All modules are identical, the only difference being the size. “We calculated annual savings of 300,000 Euros, just in fuel alone, with an estimated 2,000 tonnes of CO2 to be cut.” These fuel and CO2 savings on a vessel of this size would generate a payback period of 5 years based on the cost of conventional diesel fuel.
Wavefoils’ next planned installation is for a 22m ambulance vessel. The reduction in resistance is particularly important for a vessel like this due to its purpose. “The comfort level is key on this because of patients with a broken back, for example. With the fins they could have a speed of 10 knots more and retain the same comfort level as a similar vessel without foils,” Mr Paulsen explained.
Presently, the fins are only suited to high-speed vessels of sizes up to 200m. “Over 200m we have found some examples that make sense,” Mr Paulsen clarified to VPO Global. “However, it really depends on where they operate, the length of the ship compared to the length of the normal waves and the height of the waves.”
As the bow fins come in a small modular unit, they can be easily installed in around two weeks, Mr Paulsen confirmed. This also makes it easy for the whole unit to be extracted and transported elsewhere for repair or maintenance work, allowing the vessel to continue operation with minimal down-time. The larger units are constructed from steel, while aluminium is the primary material for the medium size fins. The foils on the larger units are flexible and composite, while the smaller ones are made from normal propeller rods. “All apart from composite ones are biodegradable,” said Mr Paulsen. He also confirmed that they are currently carrying out research into biodegradable options. “When these are as good as the ones we make today, then we will make the change.”
Source: VPO Global