Tortuga ATB pusher tugboat adds to American LNG bunkering capacity

The tug and barge pair up through a Beacon Finland JAK coupler system.
The 4,000 hp Tortuga pushes the barge Clean Everglades, which can hold 5,400 cubic meters of LNG.
The 4,000 hp Tortuga pushes the barge Clean Everglades, which can hold 5,400 cubic meters of LNG.


Tortuga
| Seaside LNG, Jacksonville, Fla.

It’s a working boat with some glamorous clients. The articulated tug-barge (ATB) pusher tug Tortuga and its barge, Clean Everglades, deliver liquefied natural gas (LNG) to cruise ships — including the biggest one of its kind in the world. 

That massive cruise ship, Icon of the Seas, launched in January. The nearly 1,200-foot vessel can carry about 5,600 passengers, plus a crew of nearly 2,400, and features multiple waterslides, seven swimming pools, nine whirlpools, an ice-skating rink, a built-in waterfall and about 40 restaurants and nightclubs.

Icon of the Seas also was the first Royal Caribbean vessel to run on LNG, which burns cleaner than traditional fuels. That means no more smokestacks emitting soot particles that can land on the upper decks.

The tug and barge pair up through a Beacon Finland JAK coupler system.
The tug and barge pair up through a Beacon Finland JAK
coupler system.

Today, Tortuga/Clean Everglades and its earlier sister ATB, Polaris/Clean Canaveral, routinely travel the roughly 270 nautical miles from near Jacksonville, Fla., to Miami, where they meet up with Icon of the Seas and bunker the ship with LNG.

“We have been doing these deliveries on a weekly basis,” said Tom Sullivan, chief operating officer for Polaris New Energy and parent company Seaside LNG.

Seaside LNG owns the ATB as well as a 50 percent stake with Berkshire Hathaway in the Jax LNG terminal at Dames Point near Jacksonville. 

Tortuga/Clean Everglades is the latest LNG-bunkering ATB to hit the U.S. market, and Sullivan and others involved in building the vessels said they have much in common with sister vessels Polaris/Clean Canaveral delivered in December 2021. However, the very existence of the ATB points toward trends that are transforming the maritime industry.

“Right now, our long-term plan is to build about eight more ATBs,” Sullivan said. “But one at a time. As more LNG-powered ships currently under construction come out, we will increase our fleet to support these low-emission vessels.”

Tortuga was built by Master Boat Builders in Coden, Ala., and delivered in December 2023. Its accompanying barge, Clean Everglades, was built at Fincantieri Bay Shipbuilding in Sturgeon Bay, Wis., and delivered in October 2023. 

The tug and the barge then traveled separately to Jacksonville, where Sullivan’s companies have an LNG facility at Dames Point. The combined ATB is 425 feet long. A pneumatic Beacon Finland JAK 400 coupling system connects the two vessels, eliminating potential concerns associated with hydraulic oil.  

The ATB went through extensive testing in January and completed its first bunkering mission at the end of that month. Polaris/Clean Canaveral and Tortuga/Clean Everglades have completed multiple bunkering missions to cruise ships under brands such as Disney, Carnival and Royal Caribbean, as well as to car carriers for the companies Siem and NYK, some tanker ships and multiple containerships for the global shipping company CMA CGM, Sullivan said.

Seaside LNG hired McAllister Towing to operate Polaris/Clean Canaveral and TOTE Services to operate Tortuga/Clean Everglades. Each ATB runs with a seven-person crew; Jeff Serebrin and Jason Cirrincione serve as captains on Polaris, while Evan Beeman and Ted Blair are captains on Tortuga.

Perhaps the most defining characteristic of Tortuga is its propulsion system that aims for maneuverability, which is critical for sidling up to big ships like Icon of the Seas. Thompson Tractor Co. of Spanish Fort, Ala., supplied the Caterpillar engines and related components for Tortuga. Richard Tremayne, general manager of the marine division at Thompson, said Tortuga uses the same engine configuration that’s proven successful in Polaris. 

Two Caterpillar 3512E engines turn Berg MTA 524 z-drives for enhanced power and maneuverability.
Two Caterpillar 3512E engines turn Berg MTA 524 z-drives for enhanced power and maneuverability.

Like Polaris, Tortuga has two Tier 4 Caterpillar 3512E diesel engines capable of 2,000 hp at 1,600 rpm, combined with two Berg MTA 524 azimuthing thrusters that can rotate 360 degrees. The propulsion system includes slip-to-idle clutches.

“And what they do is allow a captain to have much more fine control at the very, very lowest end of the speed range in maneuvering,” Tremayne said. “When you go to clutch in, the boat doesn’t lurch. There’s no bump. You just move the throttles and the boat starts moving.”

The maneuverability of the azimuthing thrusters means the boat doesn’t need as much power. “They provide the opportunity for a captain to be able to save a lot of fuel in maneuvering situations,” Tremayne added.

At full power, the engines each consume 93 gallons of fuel per hour, for a total of 186 gallons per hour, he said. The propulsion system is designed to push the barge at 10 knots.

The system for maintaining LNG temperature and pressure is a core piece of Tortuga/Clean Everglades. Cooling the barge storage system is a Turbo-Brayton 350 cryocooler from Air Liquide, Sullivan said. Storing the liquefied gas are four IMO Type C tanks of about 1,390 cubic meters each, supplied by Wartsila. 

This cooling equipment mirrors the equipment in the earlier vessel. But there are other improvements between Polaris and the second boat, Tortuga. Sullivan met with the crew and asked for recommendations to make the second ATB even better than the first. The crew came back with some smart design upgrades. Among them were modifying the pilothouse console, allowing mariners to walk up to the front window and look down to the deck crew. 

“We changed the crane from a fixed crane to a telescopic crane,” Sullivan noted. “It’s easier for them to get things on and off the tug with the crane when they’re still in the notch [of the barge.] That’s another example of one of the things they had us change.” 

Polaris and Clean Canaveral launched in 2021 and can carry about 5,400 cubic meters of LNG. Tortuga/Clean Everglades have similar capacities. 

Crew recommended changes to the wheelhouse console for better overall visibility.
crew recommended changes to the wheelhouse console for better overall visibility.

Karl Keiger, chief naval architect with Guarino & Cox LLC, designed Tortuga. He mentioned a related tweak to improve visibility. “Two of the windows in the pilothouse were changed to opening-type windows so that the crew can open the window and stick their head out for better visibility. That’s for coupling and uncoupling from the barge.”

New American Bureau of Shipping (ABS) regulations required the boat to add a second shipboard fire pump to provide water for onboard firefighting, Keiger said. As such, Tortuga now has two 25-hp Aurora 3801 fire pumps. This system is separate from the equipment that runs the barge’s built-in emergency fire monitor.

Also to comply with new ABS rules, designers reconfigured Tortuga’s emissions control system. Keiger said designers reconfigured the area to create an empty space between the diesel exhaust fluid tanks and the fuel tanks. 

Parts of the maritime industry are transitioning to LNG propulsion. But even proponents acknowledge the industry will likely move on to other fuels eventually. Sullivan sees an upside to its use in the meantime. “LNG is a bridge to even cleaner fuels,” he said. “LNG, I think, is the cleanest fuel you can get right now. And we’re looking at things like methanol, ammonia, hydrogen.” 

As he sees it, though, adoption of such fuels is still a ways off. “But right now, it’s LNG. It’s not those other things. So, it’s a great bridge right now to get rid of a lot of emissions that are associated with diesel fuel and switch to a very clean fuel, like liquefied natural gas.”

That means for now, more and more boats like Tortuga will travel on the high seas.