All-electric tugs and pilot boats: Are they ready for prime time?

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Courtesy Damen Group
The Ports of Auckland has ordered a full-size, all-electric tugboat from Damen Shipyards based on the builder’s RSD Tug 2513, shown above assisting the LPG tanker PGC Strident Force. Damen says the electric tug will be able to generate a 70-tonne bollard pull, which is comparable to the diesel-powered version.

There are electric ferries and tour boats, along with proposals for fully electric containerships, bunker tankers and barges. But how will all-electric vessels measure up to the extreme power demands of harbor tugs, or the distance and speed requirements of pilot boats?

Two companies have taken on these challenges. In July, the Ports of Auckland in New Zealand ordered the world’s first full-size, fully electric ship-handling tug from Damen Shipyards of the Netherlands. The acquisition of the RSD-E Tug 2513 will help Auckland toward its goal of becoming emissions-free by 2040. And the naval architecture firm Robert Allan Ltd. of Vancouver, British Columbia, unveiled plans for an all-electric pilot boat in 2018.

Both companies are using existing designs and boats, reconfiguring them for all-electric propulsion. Damen’s all-electric tug is based on an RSD (reversed stern drive) model that is fuel-efficient and meets International Maritime Organization (IMO) Tier III standards.

“Functionally, the requirements and capabilities of the tugs is the same,” said Viktoria Adzhygyrei, spokeswoman for Damen. Robert Allan is basing its all-electric aluminum pilot boat on its steel-hulled RAlly 1600.

Auckland began looking for an electric tug three years ago. “When we first looked into buying in 2016, there was nothing on the market,” said Allan D’Souza, the ports’ general manager for marine, engineering and wharf operations. Auckland then went to Damen for the project based on the ports’ satisfaction with the ASD Tug 2411.

“We looked at the request and saw it was technically possible,” said Marc Baken, a design and proposal engineer at Damen. “The next step was to consider the feasibility of full electrical operation from a business perspective.”

Damen used data from Auckland’s operations of the ASD Tug 2411 to work out the battery requirements for the RSD-E Tug 2513, which will measure 81 by 43 feet. After a collaborative process, the order for the electric tug was announced, with delivery expected by 2021.

The most impressive feature of the RSD-E is that it will generate a 70-tonne bollard pull, according to Damen. For safety reasons, the tug will have two 1,000-kW generator sets to provide enough power for it to operate at 40 tonnes bollard pull in the event of an electrical system failure, or if the vessel needs to operate beyond its battery capacity. The tug will be able to switch to the backup power in a matter of seconds, Adzhygyrei said.

The RSD-E will have two strings of batteries so that if one string fails, the other takes over. Damen would not say who will build the batteries, or what type they will be.

An electric tug’s ability to generate a 70-tonne bollard pull has been met with some skepticism in the maritime world. “For how long is my question,” said Nick Sorber, regional representative for the International Organization of Masters, Mates & Pilots (MM&P) in Portland, Ore. “Is it five seconds? Is it 20 minutes?”

Providing that much bollard pull is the real test of the batteries. “You have to have that much electrical power in the batteries to provide that power,” said Jonathan Parrott, senior naval architect at Seattle-based Jensen Maritime Consultants. “It can only provide it for a certain period of time, and then the batteries drain out. The more power you pull out, the shorter duration time you have.”

The RSD-E will be able to generate 70 tonnes of bollard pull for 30 minutes, said Matt Ball, spokesman for the Ports of Auckland. “We rarely operate the tug at a 70-tonne bollard pull and if we do, it will be for very short bursts unless we are doing something outside our normal operating mode.”

The RSD-E will be able to complete three operations without recharging, Adzhygyrei said, and it will take two hours to fully recharge. The 1.5-MW charging station is based on technology already being used in the auto industry, with four cables on the vessel connecting to the station.

The RAlly 1600-E, designed by Robert Allan Ltd., has Danfoss permanent magnet motors and a 72-module battery system capable of providing 815 kW. Top speed is 20 knots and the range is five nautical miles, according to RAL.

Courtesy Robert Allan Ltd.

In 2018, Robert Allan Ltd. tackled the challenge of creating an all-electric pilot boat. Using the same hull form and general layout as the RAlly 1600, the company took out the diesel equipment and replaced it with electric propulsion and battery equipment, and switched to an aluminum hull. The boat is 52 feet long and has a 16-foot beam.

“Once we dispensed with the diesel engines, gensets and diesel fuel, we were left with enough space and weight-carrying capacity to integrate the new powering and energy storage systems,” wrote Robin Stapleton, an electromechanical engineer and project manager at Robert Allan, in The Journal of Ocean Technology.

The RAlly 1600-E is designed with Danfoss permanent magnet motors rated at 500 kW at 2,800 rpm. Standard ZF or Twin Disc 3:1 reduction gears connect to open fixed-pitch propellers. The battery system is composed of 72 modules from Spear Power Systems providing 815 kW of energy. The battery system is designed for maritime use and is liquid cooled.

At 20 knots, the boat has a range of five nautical miles from its berth to a ship and back. “This seems low, but actually covers a significant portion of pilotage operations,” Stapleton said. With a high-capacity charging station, the tug could be fully recharged in less than an hour.

But many pilots say that five nautical miles, even one way, is a short range. “Just on the river, we can go more than five miles,” Sorber said, referring to the Columbia River in Oregon. “And that’s not going against the ebb tide or something that’s going to strain the batteries more. Five miles is not much.”

Sorber doubted that the Columbia River Bar Pilots would want to use an electric pilot boat. However, the Columbia Bar is one of the most demanding pilot runs in the country.

“They’re not going to want to go out over the bar on something electric and wonder if they’re going to make it back,” he said. “I know I wouldn’t.”

Stapleton acknowledged that a negative for all-electric boats is cost. Robert Allan estimates that the RAlly 1600-E could cost $1 million more (Canadian) than the steel, diesel-powered version. He pointed out that government programs to reduce emissions could help reduce the price tag.

In the case of the RSD-E Tug 2513, the Ports of Auckland is paying the entire cost, with no grants or subsidies. The electric tug will cost twice that of a diesel, the operator said, including the cost of the charging infrastructure. But Auckland also projects a $12 million savings in operating costs over the 25-year lifetime of the tug.

In addition to cost, there are concerns for operators about venturing into unproven technology in the tug and pilot boat sectors. “It would be really scary for a business owner to say, ‘Here’s $20 million, let me know if it works,’” Sorber said about the prospect of ordering electric tugs.

Steve Shaver, president of Shaver Transportation in Portland, Ore., said the company looked into buying a hybrid tug three or four years ago. “We were going to be one of the potential leaders in the industry, and I got a little concerned about getting ahead of ourselves,” he said.

Shaver said the company does embrace new technology, calling its Tier 4 newbuild Samantha S. “probably the most sophisticated tug in the country right now.” But the concept of an all-electric boat is different.

“To get into a whole different area that we haven’t dealt with before is a little daunting at this time until it’s more of a proven commodity,” he said.

Using the new technology also carries an operating risk. “When you’re a pilot on these tugs, there’s a lot of liability out there,” Sorber said. “If you get yourself in a position where you need the horsepower and you don’t have it, who’s going to be pointing the finger about that (after an) incident?”

Categories: Tugboats & Towing