As North America and Europe face more stringent pollution regulations and voluntary “green” programs in Long Beach, San Diego and other ports mature, commercial shipowners and operators are looking for innovative ways to improve their vessels’ energy efficiency.
The challenge is finding the right strategy, whether it includes reducing hull friction or improving overall operational efficiency to cut fuel consumption. When deciding to invest in new devices or technologies, especially those that may not yet be fully proven, careful consideration of which options best match a specific vessel type and weighing the savings potential can help avoid choosing a cost-prohibitive approach.
To assist owners and operators, the Ship Operations Cooperative Program has published the 115-page “Energy Efficiency White Paper,” released for download on July 1. Funded with $36,000 from the Maritime Administration (MarAd) and in-kind services offered by SOCP, the paper includes explanations of technologies and strategies that focus on the hull, propellers and “appendages,” renewable energy, mechanical and electrical systems, and operating practices.
Sean Caughlan, the author of the white paper and a senior marine engineer at The Glosten Associates, a naval architecture and marine engineering firm in Seattle, said energy efficiency is increasingly mandated by international regulations such as the Energy Efficiency Design Index. The EEDI requires a 30 percent improvement in efficiency of newbuilds by 2025 over an established baseline.
The Corvus lithium battery system. Battery hybridization works best for vessels that operate on short routes.
Photo courtesy Scandlines
“However, for most owners the investment is still primarily cost-driven, and investments must be justified with conventional metrics,” Caughlan said.
Since more than 50,000 merchant ships are trading internationally and only a small percentage are replaced annually, Caughlan said it is difficult to say which technologies or devices are most promising in terms of their cost-to-benefit ratio.
“Therefore, the market for retrofits is technically much larger than for newbuilds,” he said. “Some technologies are only suitable for newbuilds, some can be applied to existing vessels, and some may apply to large vessels or high-speed vessels only. There are not that many ‘one size fits all’ technologies.”
The new white paper gives shipowners and operators an evaluation tool for comparing the relative merits of various energy-efficiency measures, including technologies and operational strategies, Caughlan said. Summaries of each efficiency measure, whether a technology or operational practice, are included in five broad categories: savings potential, technology stage, life cycle cost, retrofitable and compatibility.
A SkySails wind propulsion system is deployed aboard M/V Theseus, a bulk carrier operated by Germany-based Wessels. The company claims energy savings to 10 percent to 35 percent annually, depending on route conditions.
Photo courtesy SkySails GmbH
“The paper tries to address the issue of technology maturity rather than ‘newness’ per se,” he said. “For the owner looking to implement an energy-efficiency technology, they will be most concerned with the ‘readiness’ for commercial use.”
In some cases, technology that has been around for many years may have become recently affordable. “Hull form optimization, for instance, is now affordable to implement on the design of just about any new vessel due to inexpensive computing power,” Caughlan said. While the tools now exist, many ships are designed without enough consideration for a vessel’s total resistance, even though the largest component of life cycle cost is typically fuel, the paper states.
Alex Landsburg, a naval architect and engineer who is also the technical research and program coordinator at the Society of Naval Architects and Marine Engineers in Alexandria, Va., said some of the approaches described in the paper — devices added to improve water flow through the propeller, for example — may not improve the efficiency of a well-designed hull.
“A past study by a colleague at the David Taylor Model Basin in general found that if the original hull form and propulsion system is very well designed and optimized for its operating condition, the particular device may not offer improvement,” said Landsburg, who spent nearly 40 years as the coordinator of research and development at MarAd. However, many ships are not optimized for the conditions in which they end up operating. In that case, he said, adding some of the devices could help.
M/V Estraden, a roll-on/roll-off cargo ship, features a pair of rotor sails from Helsinki-based Norsepower. The number and size of rotor sails is based on the size, speed and operating profile of the ship.
Photo courtesy Norsepower
Technologies such as advanced hull coatings, fuel consumption monitoring and voyage optimization — including weather routing and speed optimization — are becoming fairly commonplace in international shipping, Caughlan said. “Because the payback is so fast, the decision is obvious,” he said. But other technologies require more time to prove their worth. One of them is air lubrication, which utilizes compressed air injected to the underside of a hull to reduce friction. Mitsubishi and Silverstream Technologies have developed air lubrication systems that are in the early stages of commercialization.
Among mechanical systems, variable-speed generators are considered attractive for their added level of flexibility and efficiency over conventional diesel-electric propulsion, the paper states. “Both Siemens and ABB (Marine Systems) have put a lot of marketing dollars into promoting this technology, but with fuel prices down, the uptake has slowed,” Caughlan said.
Battery hybrid and electric systems are also generating increasing interest, mostly in the passenger vessel sector as the cost of batteries plummets. The technology utilizes energy storage to maximize efficiency and allows a vessel to take advantage of other sources of power, including solar, wind, regeneration or grid power, the paper states.
Allan Grant, vice president of business development for British Columbia-based Corvus, which has installed its batteries on some 60 vessels, said battery hybridization is going strong in the commercial maritime market. “Whether they operate with a direct drive with an electric power takeoff or a diesel-electric (generator), the batteries can assist them with running in the efficient range and saving on fuel, air emissions and maintenance,” he said.
The hull of the tanker Amalienborg has been retrofitted with the Silverstream air lubrication system.
Hybridization works best for vessels that operate for short durations. “It is good for tugboats, ferries, water taxis and commercial dive boats for LNG (liquefied natural gas) loading, and offshore supply vessels that deliver supplies, tools and equipment out to an offshore floating wind farm,” Grant said. “When idling on a tugboat or while loading cars on and off a ferry, this allows time to recharge the batteries.”
In Denmark, Corvus has equipped six Scandlines hybrid ferries — including Prinsesse Benedikte, a former diesel-electric ferry — with a Corvus AT6500 lithium battery pack. The retrofit, the world’s largest marine hybrid propulsion energy storage system ever installed at 2.6 MWh, is an important early success in the operational implementation of the technology, according to Corvus.
Some smaller ferries that operate in spurts of 30 minutes or less are going all-electric. In Norway, Norled, one of Norway’s largest ferry operators, has installed a Corvus AT6500 lithium battery system weighing only 20 tons on Ampere, the world’s first zero-emission car ferry. Siemens developed the technology for the ferry, which sails for 20-minute intervals across the fjords.
Among renewables described in the paper, wind-assisted propulsion technologies that show potential include kite sails and Flettner rotors. “While kite sails haven’t caught on yet, they have enormous energy-savings potential,” Caughlan said. Using kite sails, lifting forces generated as air passes over the wings are transferred to the vessel through tension in the towing line attached to the bow. To maximize lift, the kite flies in a figure-eight pattern, unlike other sail types that fly in one direction.
The Silverstream air lubrication system produces a bubble carpet to reduce friction.
German engineer Anton Flettner launched the first experimental ship in 1924 using Flettner rotors, vertically aligned spinning cylinders attached to the deck. Their operation is based on the Magnus effect caused by air passing over a spinning cylinder or sphere, the physics that lets baseball pitchers throw sliders and sinker balls. “They are less elegant than the kites, but there is enormous (commercial) potential since it can be retrofitted and provides very fast returns for the right operation,” Caughlan said.
In considering any new or emerging technology, shipowners and operators need to keep in mind that not every exciting new tool will deliver what it promises. “MarAd, in the age of steam propulsion, supported the building and testing of a prototype of a contra-rotating gear system that was model-tested, shown to be capable of handling up to around 20,000 horsepower and promised some 12 to 16 percent improvement in efficiency,” Landsburg said. But the intended installation on a steam-propelled tanker planned for construction in the U.S. never materialized.
While much research around the concepts in the white paper shows potential, each one should be carefully considered. “Ships involve very large capital outlays and the assets must be amortized over a long time, so there is a lot of caution exercised by owners and operators in trying something new,” Landsburg said. “The return on investment in the shipping business is not the greatest, and the operational life is a long one over which the owner must continue to be competitive to recoup his investment and make a profit.”