|FloScan monitors installed on the car ferry Wenatchee showed that reducing the vessel’s speed from 18 knots to 16 knots in off-peak runs between Bainbridge Island and Seattle saved about 1,500 gallons of fuel each day. (Courtesy Washington State Department of Transportation)|
With diesel engine manufacturers focused on keeping pace with ever-tightening emissions standards, talk of fuel efficiency is often lost amid the progress. The reality is that for most vessel operators, the technological gains that have resulted in cleaner emissions have not translated into a reduction in fuel consumption.
To realize savings, operators must run a clean ship — in every sense of the word — and monitor every drop of fuel to ensure that it is used to its maximum potential. That requires being smarter about how the ship moves through the water and incorporating the latest technology to evaluate how onboard systems work with each other.
“The big selling point (for engine manufacturers) is not usually fuel consumption; the big selling point is usually air pollution,” said Peter Kahl, manager of the Marine Engineering Division at the Global Maritime and Transportation School in Kings Point, N.Y.
“They don’t always work together. Engines are not necessarily becoming more efficient as you reduce pollution — it depends on what you’re trying to reduce. If you’re trying to reduce nitrous oxides, a lot of times an electronic-controlled engine actually decreases fuel efficiency,” he said.
To hold the line on fuel consumption while meeting emissions requirements set by the International Maritime Organization (IMO) and the U.S. Environmental Protection Agency (EPA), manufacturers have introduced a number of technologies to wring more efficiency from diesel engines: multiple fuel injectors per cylinder, electronic control of valve timing, higher compression ratios, two-stage turbocharging and improved air management systems.
The advances have allowed Wärtsilä Corp. — a leading maker of Category 3 engines, or those with a displacement of more than 30 liters per cylinder — to meet IMO Tier II and EPA Tier 2 emission standards without sacrificing fuel economy, said Marit Holmlund-Sund, senior manager of public relations and marketing communications for Wärtsilä.
“The impact on fuel efficiency is, in general, almost unchanged,” she said. “With IMO Tier III and the corresponding proposed EPA Tier 3, we are in a different situation. The solutions are still under development, but probably the result will be increased costs in the form of chemicals for the SCR (selective catalytic reduction) and/or additional fuel consumption.”
For operators, these developments will put more emphasis on “picking the low-hanging fruit” to save money on fuel, Kahl said.
“I think from a vessel owner’s standpoint, the most important thing is keeping your ship TLC: tight, lubricated and clean,” he said. “You can make one-tenth of a percent improvement in changing the diesel design, but you can make a huge improvement in controlling the hull condition, the propeller condition, the amount of steering the ship does, and just controlling the brain of the captain to get that steady speed to go across the Pacific.”
To maximize fuel efficiency, Kahl cited the need to keep the hull and rudder clean and covered with an anti-fouling coating; polishing the propeller every three or four months; and ballasting the ship correctly so it isn’t carrying unnecessary weight. Another key factor involves controlling the ship’s course with adaptive and automatic piloting systems.
“Adaptive steering is a big item, because every time you steer you increase horsepower, and when you increase horsepower you use more fuel,” he said. “With adaptive systems, the wheel is almost never touched by anyone on the open ocean — the gear steers a course automatically. If the weather increases and the rudder has to swing more, sometimes it doesn’t pay for you to make that correction because the wave form is going to bring you back to where you were.”
Autopilot systems like Sperry’s Navipilot 4000 allow the captain to choose from a selection of steering strategies to adapt to weather and load conditions based on information provided by the system. He can make course adjustments manually or rely on the automatic tuning capability of the system, generating fewer and smaller rudder movements. That reduces fuel consumption and wear and tear on the steering gear and engine.
Kahl, formerly a vessel operator with Horizon Lines, emphasized the need to maintain a steady speed to conserve fuel. He said it is particularly important for containerships, whose captains must maintain the timetables that drive the industry.
“That was the big thing: How do we save fuel?” he said. “(Containerships) run into specific problems because they are on a very strict schedule. They have to get there on time and they have to leave on time, too. If I’m the captain and I know it takes 12 days to cross the Pacific, what do I do? The first half of the trip I go really fast, and then I slow down the second half? Well, that wastes a lot of fuel. The companies track their ships, know where they are and know what their container miles are (per barrel of fuel). They’re very concerned, because ultimately they’ll have to pass that cost on to the consumer, and you don’t want to do that.”
Kahl said the benefits of maintaining a steady pace can be shown in the propeller curve, a measurement that compares drive-shaft power to the speed of the propeller in the water.
“If you run a ship and you get to the upper end (of the curve) — say you have a 30,000-horsepower engine and you move the horsepower from 25,000 to 30,000, the last 15 percent — you spend a lot more in fuel,” he said. “You waste a lot of fuel doing it. It costs you more energy pushing through the water as the ship goes faster. So if you moderate the speed of your ship, that’s where you get your best savings.”
To determine the optimum speed for the conditions and to analyze how a ship’s equipment is affecting efficiency, operators of diesel vessels are increasingly turning to fuel accountability and measurement systems. Meters are typically installed in two locations — the fuel supply line to the engine and the fuel return from the engine — to precisely measure usage. The fuel consumption rate can then be compared to engine efficiency on a monitor in the wheelhouse, allowing crewmembers to make real-time adjustments.
“For a typical fleet manager, diesel fuel is usually the second-highest budgeted item after labor,” said Jon Archenhold, industrial market manager for Flow Technology Inc., a manufacturer of fuel management systems in Tempe, Ariz. “When fuel prices soared during 2008 … some operators spent more on fuel than on labor and found themselves significantly over budget. Understanding the fuel usage on each vessel in a fleet has therefore become critical in order to make the right decisions on operational strategies — and conserve as much fuel as possible.”
Fuel management systems can be configured to monitor single or multiple engines, mechanical or electric propulsion, fixed- or controllable-pitch propellers and multiple types of fuel. In addition to onboard analysis, the data can be recorded and downloaded by a port engineer to compare engine performance on different trips and on different vessels. Operators can then experiment with vessel speed or propeller pitch angles to optimize performance.
“By seeing the actual fuel usage rates (while) under way, the operator can adjust the engine speed to pinpoint the vessel’s ‘sweet spot’ under any load or operating condition,” said Joe Dydasco, sales manager for FloScan Instrument Co. of Seattle. “This is the rpm rate which covers the most ground with the least amount of fuel consumed. … In most cases, the operator can see that just a few hundred rpm difference in engine speed can reduce fuel consumption by 20 percent or more. This can be done with little or no effect on vessel speed.”
In a study conducted by the state of Washington, FloScan monitors installed on the car ferry Wenatchee showed that reducing the vessel’s speed from 18 knots to 16 knots in off-peak runs between Bainbridge Island and Seattle saved about 1,500 gallons of fuel each day. The reduced speed added two minutes to each crossing.
“Fuel usage goes up exponentially with speed, so quite often just reducing the speed by 1 knot can save a significant amount of fuel,” Archenhold said. “Also, (monitoring) engines on a multi-engine vessel can pick up early problems … and give an indication that maintenance is required.”
For vessels with limited wheelhouse space, fuel-flow monitors can be installed on the ceiling or wall. Color-coded displays — green for “OK,” yellow for “warning” and red for “take immediate action” — make it easier for operators to interpret the data and make adjustments.
“There is no special training required of crewmembers to interpret fuel management systems,” Archenhold said. “The better ones have sunlight-readable, nighttime-dimmable, user-friendly and customizable displays. A bar graph of engine efficiency in gallons per nautical mile with a green, amber and red portion is very simple for the operator to read and keep an eye on, (making) sure it stays out of the red as much as possible.”
Archenhold said systems for single-engine vessels range from $7,000 to $20,000, depending on the features, and from $13,000 to $40,000 for twin-engine vessels. For ships with more than two engines, the cost may rise from $5,000 to $10,000 for each additional engine. The savings depend on what the operators do to change the performance of the vessel after analyzing the data.
“Savings are typically in the 5 to 10 percent range, but for some vessels, even a 2 percent savings will pay for a fuel management system in less than a year,” he said. “Annual savings of over $40,000 per vessel are not uncommon.”
Changes in how diesel fuel is formulated may contribute to better efficiency in the future. At the U.S. Merchant Marine Academy, Kahl said undergraduate research is under way on introducing ammonia into the fuel system.
“Ammonia has a lot of hydrogen attached to it,” he said. “The more hydrogen, the better off you are. They’re looking at ways of emulsifying the ammonia into the diesel fuel and running the engine.”
While advances in diesel engine design and the electronic injection and monitoring of fuel have given vessel operators more ways to save money, Kahl said they are just a small part of a broader strategy that requires smarter thinking to ensure smoother — and more efficient — sailing.
“(Diesel engine) manufacturers really look at the electronic engine for pollution control, because they have to meet those standards first,” he said. “It’s up to vessel operators to do what they can to maintain the condition of the ship and how it’s used to achieve better efficiency.” •