VESSEL REVIEW | Stax 7 – Emissions capture barge to serve tankers at California ports
US-based Stax Engineering has placed a new emissions capture barge into service.
Stax 7 will be operated within the Ports of Los Angeles and Long Beach in California, serving as a mobile emissions capture system for tankers at berth. Stax is currently under exclusive agreements to service all tankers calling at berth F209 at the Olympus Terminals facility in the Port of Long Beach and at Shell’s Mormon Island Terminal in the Port of Los Angeles.
The barge’s main role is to provide emissions capture services while vessels are at berth, ensuring compliance with the California Air Resources Board’s (CARB) emissions mandates.
“Stax barges are mobile emissions capture systems that connect directly to the exhaust stacks of docked vessels to control air pollution,” Jose Garcia, Assistant Design Engineer at Stax, told Baird Maritime. ”Engineered to operate efficiently and reliably in port environments, Stax 7 is part of our latest generation of barges, sharing key features with Stax 6 and 8.”
“Stax 7 addresses a critical gap in emissions compliance for tanker vessels, meeting rising demand at major California ports,” added Jaden Doble, Stax’s Assistant Director of System Engineering. “As of January 1, 2025, tankers calling at the Ports of Los Angeles and Long Beach must reduce emissions while at berth, and by 2027, these requirements will extend to all California ports.
“Notably, tankers face a unique challenge: they often cannot use shore power due to the significant safety risks posed by their flammable cargoes—to do so would require specialised, costly equipment. Stax offers tankers the most practical, cost-effective path to compliance.”
On July 29, CARB issued an executive order authorising Stax to provide emissions capture services to tanker vessels. Unlike alternative options that require expensive vessel retrofits or extended downtime, Stax’s system connects seamlessly to ships’ exhaust stacks, helping operators meet emissions mandates without disrupting operations.
Garcia said that one of Stax 7’s most distinctive upgrades is the use of square spuds, which anchor the barge in place while servicing vessels. Unlike the traditional cylindrical design, these square spuds are significantly stronger and eliminate binding issues common with circular alternatives. Their added weight also drives them deeper into the port bed, improving stability during operation.
The barge also features a re-engineered fuel system. A high-volume, below-deck diesel tank increases capacity by 2,500 gallons (9,500 litres) and frees up valuable deck space. This placement—coupled with a new automatic fuel distribution system that fills the day tank as needed—enhances safety by keeping fuel in a contained, protected area.
Garcia said the barge runs on renewable diesel and includes onboard systems to clean its own emissions, reducing environmental impact even further.
“With a larger working deck (176 by 44 feet) [53.6 by 13 metres], 10 feet (three metres) longer than [on] previous models, Stax 7 offers wider aisles and more space for the crew to perform maintenance and service tasks,” said Garcia. “For added protection, coaming around the barge provides secondary containment, while tanker-grade safety measures—such as handrails and cameras at the boom’s end—further enhance on-deck safety.”
Among the first newbuild barges in the owner's fleet
“With Stax’s first five barges, our team retrofitted existing vessels to support our mobile emissions capture systems,” Doble told Baird Maritime. “After gaining a clear sense of the operation demands unique to emissions capture and what would improve workflows, we set out to build Stax 7 (along with Stax 6 and 8) as completely custom-built, new platforms.
“Stax 7 is part of a new generation of barges designed from the ground up, informed by years of hands-on experience. Our goal was to make the barge lower, wider, safer, and smarter.”
Doble remarked that a lower overall height was a key design change, since the taller structure of earlier barges was not necessary for emissions capture operations.
“Safety drove every detail—from the orientation of the stairs to onboard containment systems—reflecting Stax’’s commitment to rigorous safety protocols and continuous risk management. We also prioritised a larger deck to create safer walkways and working space.”
As with the company’s earlier barges, Stax 7 had to meet CARB’s performance-based emissions control standards, with flexibility to adapt onboard technology as needed.
As the barge is not self-propelled, it relies on tug assistance for positioning. Stax has therefore established a tug agreement to improve service reliability and reduce operating costs.
The barge is fitted with three 400kVA generators, which operate only as needed to support the onboard processing systems. Also included is a proprietary regeneration system that ensures power stability and system efficiency. The design minimises energy waste while providing consistent power to critical components.
Stax 7 also boasts emissions scrubbing systems to clean its own output, reinforcing the barge’s environmental performance.
“The proprietary regeneration system on Stax 7 incorporates improvements to heaters, ducting, and controls that significantly enhance reliability and operational uptime,” said Garcia. “These upgrades have now been standardised across the Stax fleet, ensuring consistent performance on every vessel.”
The deck equipment meanwhile includes two spud winches with a combined 42,000-pound (19,000kg) lifting capacity and two capstans for secure mooring. The layout also incorporates a centralised control room alongside dedicated spaces for electrical distribution, utilities, storage, and a fully equipped workshop for on-the-spot repairs. Additional crew facilities include a climate-controlled breakroom.
The barge also carries two complete processing units and a large boom for vessel connection.
New standardised design and layout to be adopted for future vessels
“Several upgrades to the setup set Stax 7 apart,” added Garcia. “The diesel tank is now located below deck, freeing up space and keeping fuel in a more contained, protected area. We’ve also adopted square spuds for superior holding power and stability, and introduced an expanded, more intuitive operator interface to streamline system control.”
For Stax, designing the new barge was an exercise in efficiency and in integrating lessons from the company's first five barges into the first generation of custom-built barges (i.e., Stax 6, 7 and 8).
“We had to fit complex emissions capture equipment onto a barge while maintaining the minimal overall footprint required for servicing vessels in a busy port,” Garcia told Baird Maritime. “Every design decision, from tank placement to deck layout, had to balance functionality, safety, and stability within the conditions of a lower-profile barge.”
Building Stax 7 and her sister barges meanwhile came with a unique set of logistical and operational challenges, as Doble explained.
“Port space was limited throughout construction, requiring careful coordination. At the same time, increased tariffs impacted supply chains, leading to inventory holds, price fluctuations, and delays as parts cleared customs.
“This was also the first time our team built three barges in parallel, which meant scaling crew and improving assembly efficiency under tight timelines. Coordinating funding schedules alongside the physical build required close alignment between financial and operational teams.”
Through its work designing and building the new barge, Stax gained several learnings that it believes can be applied to future builds.
“We confirmed that a lower-profile design offers real benefits in stability and usability,” said Doble. “We also learned that adding larger deck drains is essential for effective rainwater management, especially with the added coaming for secondary containment. In future builds, we will incorporate upsized deck drains to ensure better flow and drainage.”
On the fabrication side, Stax identified opportunities to streamline construction and enhance safety by increasing shipyard welding, pre-installing handrails, and integrating ladders. During this process, the company also improved the quality assurance process with its partner shipyard, thus setting a new standard for how to operate in future builds.
“Lastly, we’re refining barge protection and bumper systems to boost durability and extend service life,” added Doble.
