Bisso’s new tractor tug: Tier 4 and Subchapter M

New Orleans-based Bisso Towboat Co. Inc. operates a fleet of 12 tugs with a new one set to be delivered in October. Bisso Towboat concentrates on assisting oceangoing vessels on the Mississippi River and Inner Harbor Navigational Canal. Bisso’s current president, Scott Slatten, is the fifth generation to run the company.

Bisso built the 98’x34’ Liz Alma in 1991 at Main Iron Works (MIW), Houma, La. The Liz was the first new tug the company designed specifically for ocean ship assist (The Liz Alma was sold to Robbins Maritime in 2017). Then in 1999, Bisso started construction of the first of seven tractor tugs at Main Iron that has become the backbone of the company. The 98′ design is very stable and sized perfectly for docking and undocking ships on the Mississippi River, in some tight spots. In fact, Bisso liked the design so much the company continued to build tractor tugs with similar hulls with a few changes for crew comfort and compliance. All of Bisso Towboat’s newbuilds have been built at Main Iron.

When it came time to build the eighth tractor tug, it was not as simple as picking up the phone and placing the order. This was due to increased bollard pull requirements and changes in regulations concerning EPA emissions and Subchapter M.

It would become a challenge and a journey that Bisso and Main Iron embarked upon together. The challenge was to find the solution to comply with EPA’s Tier 4 strict emissions regulations, the Coast Guard’s Subchapter M requirements, and an increase in the bollard pull from 60 to 75 tons. Then the trick was to fit everything within the 98’ hull. The result was the Andrew S, which Main Iron delivered to Bisso in late November. The 6,008-hp Andrew S is the first Tier 4 ASD tractor tug built for use on the Mississippi River. It’s also the fourth new ASD tractor tug built by Main Iron Works for Bisso Towboat in the past five years.

“It will be very similar structurally and from a profile to our last newbuild, Liz Healy, as the vast majority of the changes will be in the engine room for the SCR system and larger Z-drives and a larger bow winch and bow staple to accommodate the increased horsepower/bollard pull,” Slatten said last year. “Beyond that, we were able to pretty much use our existing design with some minor changes in tankage and hull and the above.”

Bisso's new tractor tug will have bigger engines, Z-drives, bow winch and staple compared to its last newbuild, Liz Healy. Bisso Towboat photo

Bisso’s new tractor tug has bigger engines, Z-drives, bow winch and staple compared to its last newbuild, the Liz Healy. Bisso Towboat photo

Bisso’s senior captain and vice president of training, Jonathan Davis, worked closely with Main Iron’s Benny Cenac and naval architect Ashraf Degedy, and Caterpillar’s Charlson Smith on the Andrew S. Davis, Cenac and Smith will share their story at the International WorkBoat Show Dec. 4, part of the Tugs and Coastal Towing conference program.

WorkBoat sat down with the team that collaborated on the project to get a preview of their presentation.

WorkBoat: Capt. Davis, you were faced with two different compliance issues when you decided to build the Andrew S, the EPA’s Tier 4 emissions standards and the Coast Guard’s Subchapter M regulations. How did you approach the building process given the new regs?

Davis: There were actually three issues to deal with — more bollard pull, EPA’s required Tier 4 technology and compliance with the Sub M regulations. They had to be addressed together. The propulsion solution that we chose would mean different modifications to the vessel to meet Subchapter M.

WB: What propulsion system did you go with and how did you decide?

Davis: To handle the increased power requirements we chose the proven Rolls-Royce Z-drive units and increased the size from US 205 to US 255. Then a decision had to be made with the type of NOx reduction system, all the while following the new Sub M requirements. We narrowed it down to two options, the GE’s EGR system and Caterpillar’s SCR system. We visited a GE Tier 4 complaint application on an Ingram towboat in Kentucky and a Caterpillar Tier 4 on a McAllister harbor tug in New York. Then after consultation with Main Iron Works and their naval Architect, Ashraf Degedy, the Caterpillar seemed the most likely arrangement to fit into our hull. Degedy and I visited the (Cat 3516E Tier 4, 110’) Caden Foss in San Francisco which sealed the deal. We took measurements of the extra equipment and Ashraf confirmed we could fit the package into our present hull. Then when I saw the tug working and operating from clutch to full ahead with no smoke, we were sold.

WB: From the Caterpillar team, Charlson Smith assisted Bisso with selecting the engine package for the Andrew S. Charlson, what sets the Cat Tier 4 apart?

Smith: Our 3500 Series engine is a compact and reliable engine to begin with. Five of the Bisso tractor tugs have 3516s in them already. The SCR system we use in the new 3500 Series was developed by Caterpillar. It has stood the test of time and durability on off-road vehicles, highway trucks and heavy equipment. The system utilizes diesel exhaust fluid (DEF), a urea-based fluid that is mixed with the engine’s exhaust, causing a chemical reaction that significantly reduces NOx in the exhaust. At the same time, the new 3500 Series engines maximize performance while increasing fuel efficiency. When the Bisso folks saw how the engine performs, they were impressed.

WB: At the shipyard, Main Iron worked to build the new tug to comply with Subchapter M. How did you handle the newbuild requirements?

Cenac: On this vessel, the American Bureau of Shipping (ABS) is the TPO (third party organization) overseeing the construction and outfitting. All tanks and piping were tested to check for leaks. This is something MIW always performed in house on every vessel built. For Sub M, the testing now has to be witnessed by the TPO.

WB: What are some of the changes Main Iron made to this eighth vessel to comply with Subchapter M?

Cenac: Pre-Subchapter M did not require an enclosed fill station on the side of the vessel, only fill pipes and vents. Fuel is now transferred onto the vessel via a contained station ‘box.’ Remote fuel shutdowns are now located on the outside of the engine room. The firefighting system also was changed. The CO2 system was required in order to suppress potential fires in the engine and generator rooms. This required eight CO2 cylinders sized appropriately to the cubic footage it is protecting, as well as hard piping to disperse the CO2 to the appropriate areas. The CO2 system was furnished by Hiller. The previous vessels built for Bisso by MIW also included fire pumps for exterior fire nozzle stations as well as a hard piped fire monitor on the front of the vessels’ wheelhouses.

WB: How about the SCR system? How did you accommodate the urea tankage to comply with the new regulations?

Cenac: Tanks were built out of 316 SS and welded into the port and starboard ballast tanks of the vessel. The purpose of placing the tanks here is for keeping the urea liquid at a stable temperature and also to keep the vessel’s tonnage the same. Transferring the urea from the tanks required additional pumps and piping. The urea travels from the storage tank to a dosing unit. The dosing unit injects precise amounts of urea liquid into the SCR unit. The SCR unit then burns the urea liquid into the exhaust to minimize pollutants. Stainless Steel piping and storage was required due to the highly corrosive properties of the urea liquid. Additional air compressors along with air dryers were required to separate the ship’s air and the urea system. Dryers on the air compressors are needed to eliminate moisture from being introduced into the urea system.

About the author

Kathy Bergren Smith

Kathy Bergren Smith has been a correspondent with WorkBoat since 2002. She is also a writer and photographer for the Port of Baltimore Magazine covering shipping and port activities. Smith, also a noted commercial and fine art photographer, resides in Annapolis, Md.

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