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To move energy efficiency forward, look astern
Energy-saving devices and propeller innovations from Japan offer opportunities to cut fuel consumption and improve energy efficiency
To meet tightening international emissions-reduction regulations, shipowners are looking to squeeze out as much energy efficiency as possible from their existing vessels. These regulations are aimed at lowering the carbon intensity of international shipping.
IMO’s Greenhouse Gas (GHG) strategy calls for a 50% reduction in GHG emissions by 2050 compared to 2008 and a 40% reduction in carbon intensity by 2030.
The technical approach to meeting these targets is the Energy Efficiency Index for Existing Ships (EEXI) and the operational approach is Carbon Intensity Indicators (CII).
Both of these measures will enter into force in November 2022 and become effective as of 1 January 2023. A poll of delegates at a recent Riviera Maritime Media webinar, Future-proofing your chemical tanker operations, indicated that more than half (52%) of owners are not yet prepared to comply with EEXI and CII regulations.
Fortunately, there are resources available to help shipowners assess their fleet requirements. Japan’s Nakashima Propeller, whose successful multi-bladed ECO-Cap diffuses the hub vortex, and consultancy Fluid Techno have teamed up to provide a diagnosis that improves ship performance under the EEXI and CII.
As Nakashima Propeller president Takayoshi Nakashima explains: “An incremental improvement in the fuel efficiency of huge tankers and cargo ships means a major reduction in global fuel consumption. A propeller is a small part of a large vessel but is indispensable for the ship to move forward.”
The two Japanese companies combine expertise to rate the condition of vessels already in service in relation to the EEXI standards, which essentially address the technical efficiency of ships. Having done the calculations, they are then able to propose solutions that would bring the ships up to scratch in terms of operational efficiency under CII. A report for one ship is priced at 350,000 yen [US$3,195] and takes about three weeks, following the gathering of the required information.
“52% of owners are not yet prepared to comply with EEXI and CII regulations”
“The target is ocean-going vessels that are in service, irrespective of classification,” explains Fluid Techno. “[The service] is also applicable to coastal vessels.”
The calculations are complex. As class society DNV explains, the CII requirements measure how efficiently a ship transports goods or passengers in terms of the grams of CO2 it emits per cargo-carrying and nautical mile. Once that is done, the ship is given an annual rating, ranging from A to E. The CII requirements are different from EEXI. While the former is all about actual emissions in operation, the latter is a one-time certification based on design parameters.
The clock is ticking on improving the performance of today’s ships. The CII requirements will apply from 2023 for all internationally-trading cargo, ropax and cruise vessels above 5,000 gwt. After 2023 the standards become more stringent.
In April, Nakashima Propellers acquired Hamburg-based Becker Marine Systems (BMS) to boost its ability to offer shipowners and shipbuilders integrated, turnkey propulsion solutions for meeting the more stringent energy efficiency standards, higher emissions reductions and fuel-saving requirements under EEXI.
During a virtual press event, BMS managing partners Dirk Lehmann and Henning Kuhlmann said the co-operation between the two firms was a “perfect fit” because Becker Marine Systems are “expert suppliers in front of and behind the propeller with well-known products such as the Becker Mewis Duct and the Becker Rudder family” and Nakashima Propeller is a “globally leading propeller manufacturer”.
BMS, for example, offers the Becker Performance Package, a combination of a Becker Rudder and Becker Mewis Duct to maximise possible energy savings in front of and behind the propeller.
Bulb fins
Meanwhile, MOL Techno-Trade’s latest, advanced version of its long-running propeller boss cap fin (PBCF) design has been steadily accumulating orders since its introduction in mid-2017 on the back of exhaustive analysis, based on a wide variety of vessels, that reveal fuel savings of up to 5%.
But now MOL Techno-Trade is taking the innovation a step further. The group has combined resources with Japan Hamworthy, a specialist in high-lift rudders such as the schilling, to add an energy-saving rudder to the boss cap that features bulb fins.
As the researchers told a recent conference, the rudder is married to the PBCF in an arrangement that boosts the latter’s proven benefit. First, there is a high-thrust blade section and a horn that is twisted to further increase thrust. Second, the size of the end plate located under the rudder has been decreased to reduce resistance and the propeller-induced ‘swirl’ that also affects propulsion. And finally, the large central bulb has been flattened at the front.
So far, a series of parameter studies suggest the researchers are on the right track. Using computation fluid dynamics (CFD) and a tank tow test on a bulk carrier and a Panamax car carrier, the rudder-PBCF combination showed gains in horsepower of up to 5.7%, a more than worthwhile result. “Generally, it is difficult to improve horsepower by 4% or more with a normal reaction rudder,” the researchers explained.
The essential principle of PBCF, the manufacturer explains, is that the fins rectify the strong downflow from the propeller’s trailing edge so that the ‘rotable component’ – a measure of drag – is reduced and thrust thereby increased. A major preoccupation of the research was to establish no loss in the effectiveness of the steering.
With the energy-saving rudder married to the PBCF, it seems the benefits accrue even further. Sales are set for 2021.
“A rudder-PBCF combination showed gains in horsepower of up to 5.7%”
Before working on this latest innovation, MOL Techno-Trade had already responded to tougher IMO regulations on propulsion efficiency by refining PBCF in three ways that have further reduced the hub vortex. The overall result was a boost to the efficiency of “the main propeller rotation”, the company reports. The numbers tell the story, claims MOL Techno-Trade. The improvement in fuel savings for the modern eco-ship is said to be 2% up on a conventional design.
According to more detailed studies, the innovation resulted in a 4.5% fuel saving on a 7,500 m³ LPG tanker at design speed, significantly better than with the original PBCF. At the other end of the scale, the fuel gains on a 28,000 dwt bulk carrier were assessed at 4.7%, and at 2.2% on a 35,000 dwt chemical tanker. Similar results were achieved with a 320,000 dwt VLCC, both ballasted and laden at speeds, travelling at speeds of up to 16 knots.
Advanced PBCF also delivers benefits for the marine environment by trimming vibration at the stern and, as a consequence, underwater noise. A series of tank tests show a reduction of about five decibels in a range between 100-1,000 kHz. This is achieved through the virtual elimination of hub vortex cavitation, one of the main causes of below-surface disturbance.
Shipowners have embraced the mark 2 version of PBCF. Within 20 months of the original launch, well over 250 orders were booked for vessels covering the shipping spectrum, from bulk carriers to wood-chip ships.
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