The future-proofed bulk carrier

Questions from the webinar audience

Anemoi recently took part in the ‘Future Proofed Bulk Carrier’ webinar hosted by Riviera Maritime Media. You can watch the recording on their website or view our presentation, which centred around EEXI.

During the webinar, the audience asked some interesting questions about Rotor Sails. The answers to these can be found below.

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When you are talking about installing Rotor Sails, what percentage of cargo capacity reduction may occur due to extra weight and volume reduction?

As with any other vessel equipment, Rotor Sails add mass to the vessel. As an example, a typical installation on a 114,000 dwt Aframax Tanker of 4no. 5x35m Rotor Sails would add ~200t of mass to the vessel, reducing the deadweight by 200t. This is less than 0.2% reduction for a fuel and emissions saving of about 23%. Our systems in no way impact the cargo hold /tank volume, all major structures are above deck.


Do Rotor Sails hamper cargo discharge?

Anemoi has a range of Deployment Systems designed to alleviate impact on cargo handling. The first is our unique and patented Rail System, which allows Rotor Sails to move about the deck (transversely or longitudinally) on a rail prior to port operations. This system was installed on the m/v Afros, which has since visited over 40 ports and experienced no port rejections or delays. We also have folding Rotor Sail options, with which the Rotor can be lowered from vertical to horizontal reducing air draft constraints.


What is the service life of an Anemoi Flettner Rotor and can it be transferred from one ship to another at the end of the ship’s service life?

Anemoi Rotor Sails have a design life of 25-years, which aligns to the average lifespan of a commercial Bulk Carrier. A key benefit of Rotor Sails is that they are re-deployable across the fleet. For example, If retrofitting Rotor Sails on an older ship, the technology can be moved to another vessel once the original ship comes to the end of its useful life, therefore securing investment in the technology.


In the presentation, you use an IMO average to calculate the efficiency improvement, but how much can the deviation be depending on a vessel’s operating route?

To avoid significant complexity and to align to the EEDI approach, the IMO developed the “Global Wind Matrix” to determine the wind conditions experienced by a globally trading vessel for compliance purposes. In reality, the savings will depend on the actual trade of the vessel and we assess performance based on typical trade routes of our Clients.. Typically, operation in the North Atlantic, Pacific Ocean and S. America – Asia trade will see higher or similar savings to the IMO matrix. Operation in the Middle East – Asia and E. Australia – Asia trade will see lower savings than the IMO matrix.


DNV mentioned that wind propulsion contributes 4 % to EEXI, while actual savings seem better. Do you see this changing in future?

Clearer guidance on the calculation methods will follow post MEPC76. However, it is also worth noting that the EEXI reduction is highly variable depending primarily on the size of the vessel and number and area of Rotor Sails installed. Typically, in our estimations we find that EEXI reductions of up to 10% are possible without reducing the speed of the vessel, which is often enough to move across a compliance phase threshold on its own. However, if speed reduction (through Engine Power Limitation (EPL)) is implemented, EEXI savings from Rotor Sails are significantly increased. Rotor Sails therefore enable compliance with much lower EPL reductions as compared to the case without Rotor Sails.


What is the statistical database that EEXI is measured/baselined against? Is this from IMO itself?

It is currently proposed that the EEXI framework will use the same calculation method as EEDI. Within the EEDI calculation there is already an approved method for calculating the performance benefits of Rotor Sails (IMO MEPC.1/Circ.815). This method includes a “Global Wind Probability Matrix”, which defines the probability of a vessel encountering each wind condition. This matrix is approved by the IMO and is used within the EEDI/EEXI to calculate the probable performance benefit of Rotor Sails.


Does the Rotor Sail affect have an impact on vessel sea behaviour, such as introducing a sideways tendency or heeling?

Like all Wind Assisted Propulsion (WAP) devices, Rotor Sails produce sideways forces in certain wind angles, which requires the rudder and hull to compensate. This creates drag, but this is far outweighed by the performance gains from the system.  Our control system automatically adjusts the speed of our Rotors to reduce the side forces (minimising rudder angles) to maximise net fuel savings. The integration of the wind propulsion with the main vessel propulsion is important. All applicable forces on the vessel are taken into account within our evaluation.


How do you ensure the survivability of the Rotor Sails under extreme wind conditions greater than 60 knots?

Our system is certified against Class rules which require the Rotor Sail to withstand the most severe environmental conditions including a 120kts wind speed, simultaneously applied with extreme heel angles.  The control system can operate the rotors in wind speeds up to 35m/s (70kts); above this wind speed, the system automatically stops the rotors so that they do not generate thrust.


Rotor Sails require changing route through harsh weather. how do you feel this could work taking in account the human factor (crew’s fatigue)?

To unlock the maximum potential from the technology, weather routing considering the benefits of Rotor Sails can be utilised (though not essential). Human factors (e.g. crew fatigue) are critical and ultimately the crew will select the vessel speed and course based on the REAL environmental conditions. As always with or without wind propulsion there will be a trade-off between human factors, safety, performance and other operational requirements.


Do you think that a combination of wind propulsion and other technologies could be a good combination to achieve the relevant EEXI/EEDI numbers?

Rotor Sails are a form of propulsion – they provide power to a vessel. This makes them complimentary to other Energy Saving Technologies (ESTs) such as Air Lubrication, wave energy, hybrid propulsion etc. to unlock even more significant gains. We strongly believe that the future “Zero Emissions” vessel will rely on a combination of technologies including wind propulsion.


Can Rotor Sails alone can provide the full propulsion thrust?

Anemoi Rotor Sails provide auxiliary propulsion in the case of retrofitting to bulk carriers. The main engine will always be the primary propulsion system, however for future newbuild designs we are working on projects that could see wind as a primary propulsion source.