According to NASA, the word propulsion “is derived from two Latin words: pro meaning before or forwards and pellere meaning to drive. Propulsion means to push forward or drive an object forward. A propulsion system is a machine that produces thrust to push an object forward.” Put said machine in a boat instead of a rocket and marine propulsion is created.
Of course, boats have been using propulsion methods to push forward a lot longer than rockets have. And boats can do something propulsion systems on rockets can’t do: Pull an object backward.
RIVER RUNNERS
Towboats that run product in barges along U.S. waterways are unlike any other type of workboat. They haul thousands of tons of product loaded into barges that they push out ahead of them. It’s the towboat that controls where the tow is going, whether the tow is made up of a single barge or 26 barges or whatever number.
Tow control on the Mississippi River can be more challenging than on other waterways because of the river’s size, current, its locks and dam systems, and heavy traffic.
Propulsion for these boats comes from a combination of engines, gears and propellers or Z-drives, all of which can be bought separately or in a package.
Chem Carriers, Plaquemine, La., is an inland marine liquid transportation company that currently operates between Corpus Christi, Texas, and New Orleans. Chem Carriers’ current fleet consists of 13 towboats, 52 inland tank barges, and a 174-barge capacity fleeting service located at mile marker 207 on the Lower Mississippi River.
The company recently replaced the Z-drive units in two of its retractable pushboats — the 86.4'x30'x10' Capt. Frank Banta Jr. and the 78.7'x28'x10' Capt. Robert J. Banta. The refitting was done at Verret Shipyard, also located in Plaquemine.
Chem Carriers chose Twin Disc’s Veth Z-drive rudder propellers for the upgrade.
“We provided a pair of VZ-900 Z-drive units capable of a continuous-duty rating of 1,298 hp,” said Andy Walker, vice president operations at Sewart Supply, the Twin Disc distributor in Morgan City, La., that supplied the rudder propellers for the refits. The drives in each pushboat are connected to twin S12R Mitsubishi diesels each producing 1,260 hp at 1,600 rpm.
Walker said the Veth Z-drive allows for maximum maneuverability through full 360° thrust vectoring, meaning there’s no need for a reverse clutch. In addition, the Veth Z-drive offers a compact design and flexibility in the placement and mounting of the boat’s engines, helping to reduce engine noise.
“These units have a compact design featuring an integrated hydraulic clutch and steering system, reducing the number of hoses and equipment throughout the engine room,” said Walker. “Its compact design really helps in engine room space, making it easier to service them and to work around them.”
Each unit comes with a custom enclosed foundation box built to allow the unit to drop into the existing outer well in the boat. The heavy-duty lower gearbox includes a 1,700-mm propeller with nozzles designed for high thrust at low speeds. “The props and nozzles allow the boat to increase thrust at lower speeds,” said Walker. “The Veth units can handle the wear and tear of the inland waterway market.”
Veth prides itself on its ability to mate its drives to any hull design, said Walker. “And we can make up to any engine out there.”
Walker said the Z-drives, controls, pilot station, and the rest of the equipment for the refit are only part of the whole process. “Service and support are vitally important,” he said. “A boat sitting at the dock is costing its owner money. We deliver and maintain the equipment throughout. Sewart Supply is the best at reliable service and support. You can count on us to get you back up and running.”
Thrust is only part of the answer when it comes to getting a tow up and down the river. Rudders control the steering of the vessel. A boat that has excellent propulsion but poor steering isn’t much good. The two must work in conjunction to safely and efficiently move barges up and down the waterway.
CT Marine is a naval architect/marine engineering firm located in Edgecomb, Maine. The firm has developed what it calls its TwinDIFF system, which has been engineered primarily to maintain foil lift rather than block the water.
“The rudders are placed behind the props operating at different angles,” said CT Marine’s owner Christian Townsend. “This gives the boat more maneuverability, good side thrust, and a 10% to 12% fuel savings.”
The TwinDIFF package includes rudder trunks for the hull, the completed rudders, hubs, linkage, hydraulics, “anything to do with steering,” said Townsend.
CT Marine has installed its Twin-DIFF system on more than 25 vessels so far and is ready to market the system worldwide. “This is the year that we are really pushing it,” said Townsend. “We are going to start in-house production in 2025 with turn-key TwinDIFF flanking and steering systems.”
Operators that are currently using the TwinDIFF system on their boats include Tidewater Barge Lines, Vancouver, Wash.; Ingram Marine Group, Nashville, Tenn.; Cenac Marine Services, Houma, La.; Hines Furlong Lines, Paducah, Ky; American Commercial Barge Line (ACBL), Jeffersonville, Ind.; Marquette Transportation and Towing Co., St. Rose, La.; Express Marine Inc., Dresher, Pa.; Kirby Corp.’s Higman Barge Lines, Channelview, Texas; and the Army Corps of Engineers.
In 2020, C&C Marine and Repair, Belle Chasse, La., delivered the 170'x50'x11'6" towboat Scarlett Rose Furlong to Hines Furlong Lines. CT Marine and Hyperion Marine Group, Portland, Maine, designed the vessel and included the TwinDIFF system with CT28SL Kort nozzles with Easy Flow strut and CT inland propellers.
Main propulsion comes from three Tier 3 Cummins QSK60-M diesel engines producing a total of 6,600 hp. The mains connect to the TwinDIFF system through Reintjes WAF 1173 H/V reduction gears with a reduction ratio of 7.429:1.
Besides the fuel savings, Townsend said his TwinDIFF system gives any boat the ability to drive the head of the tow and flank less, the means to remove shaft and prop without dropping the rudders, less vibration, and 25% better steering force over conventional rudder systems. “I can convert any boat on the river to TwinDIFF,” said Townsend.
The TwinDIFF system doesn’t use Z-drives on inland towboats even though they are popular with other designers. “Z-drives coming south on the river are superior, but, going north, a 6,000-hp boat with a 90" prop, you have to drop the diameter of the prop by 20%,” said Townsend. “Z-drives can’t go upriver like the conventional shafts and props.”
CT Marine’s TwinDIFF system is also part of the propulsion package for the 200'x50'x12'6" towboat Mariner built by C&C Marine and Repair and delivered to ACBL at the end of 2024.
Main propulsion for the 11,000-hp towboat comes from twin Caterpillar C280-12 diesel engines connected to Hung Shin 5-bladed propellers through Reintjes WAF6755 marine gears. CT Marine handled the steering and controls.
ACBL officials said the Mariner is the largest towboat built in the U.S. in 50 years. Townsend said Mariner is the largest twin-screw towboat ever built for the rivers. “We have spent four years and probably 24,000-plus hours of engineering on this project,” he said.
CREW TRANSFER VESSELS
One of the first actions taken by President Donald Trump as he began his second term in office was to declare an energy emergency. The declaration is designed to streamline permitting and expand drilling for oil and gas, while ending federal leasing for wind energy, including offshore wind farms.
“The golden age of America starts right now,” Trump said after taking the oath of office in Washington, D.C., Jan. 20. Trump said he will “reverse all the betrayals…From this moment America’s decline is over.”
Trump declared a “national energy emergency…We will drill, baby, drill.”
For now, the withdrawal will not affect rights under existing leases in the withdrawn areas, but the Trump administration is requiring “a comprehensive review of the ecological, economic, and environmental necessity of terminating or amending any existing wind energy leases, identifying any legal bases for such removal.” That will bring “a report with recommendations to the president, through the assistant to the president for economic policy.”
All that said, work continues on existing offshore leases. Part of that work is the construction and operation of crew transfer vessels (CTV) that carry people to and from the offshore windmills that are the heart of the industry.
In regard to propulsion on CTVs, Volvo Penta’s Integrated Performance System (IPS) packages are very popular. The engine manufacturer sells the packages as fully integrated, designed to perform in various conditions, provide high maneuverability and productivity, and optimize fuel efficiency.
“It’s a plug-and-play system with an easy install process and a reduction in fuel use compared to traditional inboard shaft engines,” said Dave Brown, Volvo Penta's director, marine diesel sales. “IPS allows the boat to safely go out in a rougher sea state, safely put the vessel up against a piling, and hold it there without cavitation.”
Brown said there are 14 IPS-powered CTVs working in U.S. waters off the East Coast or currently under construction at American shipyards. “We have a great torque curve,” he said. “They have to run the boats slower off the East Coast because of the right whale restrictions. At 40% throttle, you get 95% torque.”
Senesco Marine, North Kingstown, R.I., late last year launched a new Jones Act-compliant CTV for its sister company, WindServe Marine. The new vessel, WindServe Spartan, marked the final boat of a six-vessel contract with WindServe. The aluminum catamaran was designed by BMT, Houston, and measures 95'x30' with a 5'6" draft.
Compared with the first four CTVs, the WindServe Spartan has an engine control room that is extended by 6' to allow for conversion to hybrid power.
“We’re not supplying the hybrid system at this time, but in the event a customer in the future wants that, there’s enough room in the back of the engine room to go hybrid,” Ted Williams, Senesco’s president, told WorkBoat.
The new CTV is equipped with quad Volvo Penta D13 main engines, each rated at 690 hp at 2,300 rpm and connected to a Volvo Penta IPS 900 propulsion system. The vessel has Volvo joystick controls, including a dynamic positioning system feature that allows the vessel to maintain its position and heading despite strong winds and current.
“Volvo’s got a really good support network here in the U.S. — tech and parts and service,” said Brown. “We also have great distributor partners along the East Coast if an event occurs.”
Blount Boats, Warren, R.I., delivered the 98.4'x36.7' CTV Guarder to American Offshore Services (A-O-S), Providence, R.I., at the end of November. It has capacity to accommodate 24 passengers.
The hybrid-ready newbuild is the third G-class series CTV delivered to A-O-S in 2024. The company is a partnership between Swedish CTV operator Northern Offshore Services and U.S.-based investment firm Orion Infrastructure Capital.
Main propulsion comes from a combination of Volvo Penta D13 diesels and four Volvo Penta IPS 1050 propulsion drives, two in each hull. The fully integrated system includes Volvo Penta’s GPS-based dynamic positioning system and integrated joystick controls. All subsystems are connected by Volvo Penta’s Electronic Vessel Control data network.
“We have a significant market share,” said Brown.
