Flettner Rotors have been with us for over 100 years now. They have been fitted to ships and aircraft with varying degrees of success. Taken at face value, they seem to offer free energy by harnessing the power of wind – an energy source which tends to be in abundance on the open seas. But why have we not used it so very well up to now?
What changes are driving us to rethink things now?
This is a very brief article, intended to give only a glimpse of this technology and the benefits it may hold for us.
What exactly is a Flettner Rotor? Quite simply, it’s a spinning cylinder up to 30m high, which takes advantage of a phenomenon called the Magnus Effect (after the German Physicist, Gustav Magnus, who discovered it in 1852).
Anton Flettner was the first engineer to try and apply this to a real ship and in 1924 retrofitted 2 x 15m high rotors to a converted schooner called the Buckau. The vessel successfully crossed the North Sea entirely powered by the rotors. Later in 1926, she successfully sailed from Danzig to New York via South America.
The principle of Flettner Rotors relies on the Magnus effect. Imagine if you will, a spinning cylinder (or sphere) with the rotation of the cylinder dragging air around one side of it. This creates a pressure difference across the cylinder, which in turn creates lift (or thrust) at 90o. The figure below demonstrates this quite clearly (Double click the image to play it, then hit ‘Esc’ when you’re done)
Examples of the Magnus Effect can be seen in everyday sports as well with topspin in ball games (David Beckham would never have been able to ‘bend it’ without the Magnus Effect), golf (slicing/hooking), and even paintball, where the introduction of backspin increases the pellet range. On a ship, the rotors are only effective if the wind is moving faster than 10 knots, and the angle of incidence is at least 20 Deg.
So if we have known about the Magnus Effect for over 160 years, and the concept of a Flettner propulsion system was proved nearly 100 years ago, why haven’t more vessels been fitted with them? The answer is quite simple. One word – economics.
The original concept was canned after the Buckau’s crossing of the Atlantic. The weight of the materials used required a disproportionate amount of energy required to spin the rotors compared to the benefits that could be delivered.
Fast forward some 40 to 50 years. An age of relatively cheap oil, little in the way of environmental legislation, and there was little imperative for vessel owners to innovate. Unsurprisingly then, Anton Flettner’s legacy remained largely forgotten about until recently.
Fast forward again to today where a company called Norsepower has been reinventing the rotor. They recently claimed that with the application of modern lightweight materials, their largest rotor sails can generate up to 3 MW of thrust, whilst drawing only 90kW of electrical power. This looks hugely efficient – although as an engineer, I still remain slightly sceptical. You don’t get anything for nothing in this world – except perhaps wind energy when it’s at the right angle and speed!
To be clear, it is not anticipated that these devices will fully replace ship propulsion systems. The economics of “vessel speed v’s cargo capacity” and intended trading patterns are well enough understood in our modern world and ours is now a world that will not tolerate waiting for the right wind conditions. Neither will it be particularly sympathetic to a vessel that has had to tack against the wind to save fuel.
Nevertheless, there are benefits to be had from harvesting the wind over the sea where we can. This is especially true when one considers the impending environmental legislation that the shipping world now faces.
New IMO legislation requires sulphur limits in bunker fuels to be cut from 3.5% to 0.5% by 2020. Having done little more than talk about it up to this point, vessel owners have been pushed into a corner where they have no choice but to innovate. I’m not suggesting that this is the only technology that will help vessel owners meet the IMO requirements as there are other alternatives such as scrubbers or low sulphur fuels, the latter of which has recently been estimated to push the cost of crude oil upwards of $100 a barrel post-2020.
Could it then be that this is an invention who’s time has finally arrived? Maybe, but it’s not quite as simple as that. It won’t work on every vessel type – I can see there being a couple of issues with aircraft carriers for example….. Joking aside, there are clearly some criteria to be met and issues to be resolved when retro-fitting Flettners to various vessels. For instance:
Norsepower certainly believes there is a future for the Flettner Rotor.
To date they have successfully installed several rotors on a number of vessels since 2014. There is now a full-scale trial on a Maersk Aframax Tanker (Pelican). The object of the trial is to determine whether the technology is applicable at scale, or not. Norsepower is confident of success and a fuel saving in the region of 7-10% on a 109,000 DWT products tanker on global shipping routes is not to be sniffed at. In a time of increased cost and regulatory pressure, on an industry that suffers from cyclical fluctuations in trading and tight margins, this may be a technology that has finally come of age.
Time will tell.
Today our guest blogger is Cristian Maxim.
Cristian is a Naval Architect who specialises mainly in mooring analysis and he is writing on the criticality of making sure our assumptions are correct.
Throughout the engineering field we are bounded by assumptions. Maybe it's the lack of available data at the time of performing calculations that requires the use of educated "guesses", or maybe it's historical data inherited from previous projects which is taken as "gospel". Whatever the reasons, as engineers, the most important thing is to validate such assumptions.
On occasion though, validating the assumptions can get overlooked until the very end of the project, and it then turns out that they are not correct. This can lead to lots of additional costs and delays to the project.
One such example is from the offshore wind farms recently installed in the UK waters. In this instance, the turbines presented a collision risk to adjacent infrastructure in the event of failure. In order to mitigate such risk, two areas were investigated:
- reduction of consequence, by means of physical protection
- reduction of probability, by means of better construction and monitoring measures.
The project had concentrated significant efforts around the reduction of probability, mainly due to the prohibitive impact on the project economics from reduction of consequence by installing physical protection.
One of the main drivers in the cost was the extent of protection required which was a considerable length of large rock dumping barriers. This was driven by seabed bathymetry data at the location, which showed a clear path of collision with the adjacent infrastructure extending for this length.
The seabed bathymetry data used in the assessment had been obtained more than 5 years before, for another project. The validity of the bathymetry data was not verified when it was acquired by wind farm installation company but it was assumed to be valid.
After a significant number of iterations of the reduction of the collision probability event, a number of the involved parties were not satisfied by the validity of the reductions attributed to improved construction and monitoring measures, due the relatively new and complex technology employed by the project which had not been fully warranted through extensive field experience. This lack of agreement led to friction among the involved parties and threatened to delay the project.
Once it became evident that physical protection was required to mitigate the risk to the existing infrastructure in the event of a failure in the wind turbine’s mooring system, then all the initial assumptions were challenged. One such assumption was the seabed bathymetry, and a new seabed bathymetry survey was commissioned for the location. The new bathymetry data indicated large natural barriers between the location of the wind farm and the infrastructure to be protected, thus reducing the length of the physical protection required i.e. by rock dumping by approximately 20 times.
By obtaining more accurate bathymetry data the prohibitive cost for the physical protection vanished overnight. The project was sanctioned based on the agreement of all parties to reduce the collision risk to the existing infrastructure by employing protective measures for the reduced length and reducing the probability by improving the construction and in service monitoring measures.
The project had been too focused on the costs guiding the decision making process, rather than addressing the quality of the input data. It demonstrated the necessity of validating basic assumptions used in the project by means of up to date re-investigations.
This week, in advance of Seawork International, we are privileged to have a guest blogger.
A-squared Engineering Solutions recently joined the SMI, as we recognised the importance of making new connections and forming lasting relationships in business. The SMI helps us to achieve this through their networking and trade show activities throughout the world. Come and see us at Seawork International win the SMI Shipyard Pavilion!
Tom Chant is the Director of Business Development and Secretary of the Society of Maritime Industries, a body that represents a wide cross-section of our amazing industry! Tom explains the role of the SMI and the work they carry out on behalf of their members all over the world.
The Society of Maritime Industries (SMI) is the voice of the UK’s marine engineering and business sector. Our activities follow our objectives of providing members with business opportunities, assisting with research and innovation, lobbying government and its agencies to improve the business environment, facilitating network opportunities and providing marketing and other services. With marine and maritime sector being so broad the SMI has six sector groups that cover the breadth of the industry including commercial and naval ships, ports and terminals infrastructure, offshore oil and gas, maritime security and safety, marine science and technology, maritime autonomous systems and marine renewable energy. Each of the groups has a Council of interested members who lead and direct the activities and input from that sector.
In a typical month there will be a range of events both in the UK and overseas. In the last 4 weeks we have had the Posidonia exhibition in Athens. The UK pavilion was visited by the Shipping Minister, Nusrat Ghani, and attended an evening networking reception at the British Ambassador’s Residence. In the UK we have had a member visit to the Port of Tyne, a Naval Attaches lunch and a hugely popular supplier conference for the Type 31 project with Babcock. The three, and soon to be four, Type 31 events have been attended by over six hundred delegates from around four hundred companies.
Work with the UK government crosses many departments including the Department for Transport and the Department for Business Energy and Industrial Strategy (BEIS) both of which are involved in the bid for a marine sector deal as part of the government’s new industrial strategy. The creation of the sector deal requires many meetings across the sector and collection of industry feedback and statistics. Tom Chant, Director at the SMI, said “I work most closely with the Department for International Trade (DIT). We await the government’s export strategy with bated breath, as UK companies are keen to export and every piece of support received is gratefully received. We are working closely as always with DIT to unlock as much support as possible for the marine sector.”
This constant activity both overseas and in the UK is delivered by the SMI team based at Threadneedle Street in the heart of the City of London. There is real passion and experience in the team who all enjoy supporting and lobbying for the UK marine sector.
Make sure you’re signed up to hear about all the activity in the sector http://www.maritimeindustries.org/E-Alerts-Sign-up-
A-Squared Engineering has completed a significant work package for SLLP134 Ltd. They have developed a low CAPEX, low OPEX production system, the Offshore Production Buoy, which can be redeployed several times during its lifetime.
The buoy is designed to enable Operators to access oil reserves which were previously thought to be uneconomical, by connecting to new or existing infrastructure.
A-Squared Engineering’s scope involved researching and recommending a suitable Class Society for the project, before developing the structural arrangements for buoy, sub-sea storage tank and gravity base in accordance with Class Society Rules. Finally, we produced a weights and centres report.