VESSEL REVIEW | Tightline – Bespoke tuna pole vessel built for South Africa's coastal waters

Sachal Shipyard in South Africa recently completed construction of a new tuna fishing vessel.

The 14.5- by five-metre (47.6- by 16-foot) Tightline is a category A-rated tuna pole vessel intended to operate all around the coast of South Africa, including offshore tuna grounds.

“Her typical duties include searching for and tracking tuna schools, catching and maintaining live bait, and conducting intensive pole-and-line fishing operations over extended periods,” Nic Stevens, Yard Manager at Sachal Shipyard, told Baird Maritime. “She is designed to cope with the often demanding sea and weather conditions associated with offshore tuna fisheries, while allowing the crew to work efficiently and safely.”

This vessel is based on Sachal Shipyard’s earlier series of 15-metre tuna pole fishing vessels, with Tightline representing the latest evolution in the design. According to Stevens, each newbuild in the range focused on improving efficiency, performance, catch quality and crew comfort, while also accommodating the specific operational requirements of each owner.

“Tightline is designed as an under-25 GRT vessel that can still carry a large quantity of tuna in RSW tanks. Working within the under-25 GRT constraint is a key part of the design philosophy, as this keeps manning costs low under SAMSA regulations – the vessel can operate with one certificated officer as master, with the rest of the complement as crew/fishermen.”

Stevens admitted, however, that the GRT limitation strictly caps enclosed volume, so the yard had to make prudent use of every available bit of space in order to fit in the crew accommodation, the galley, the heads, the machinery space, the wheelhouse, and the fish hold coamings without compromising comfort or safety.

The vessel was built to satisfy her owner’s requirements for excellent stability to reduce crew fatigue, maximum refrigerated fish tank volume within the tonnage and length constraints, and the range and capability to hunt tuna in areas far from the home port.

Significant performance and capacities in a compact hull

“A key part of the brief was that the vessel must be able to catch and carry its own live bait,” added Stevens. “To achieve this, three of the six fish tanks are fitted with live-bait circulation systems and appropriate lighting to preserve bait quality over time.

"This in turn required the vessel to handle a small purse net, which is managed using a 20-inch power block mounted for net handling and stacking into a net bin on the main deck, plus a double warping-head net winch for additional control.

The deck gear draws power from an 11kW electro-hydraulic power pack in the machinery space.

The owner also specified tuna spray bars to attract fish. Tightline is therefore fitted with stainless steel spray pipes along the starboard gunwale with small orifices to generate a fine mist on the water surface.

Two systems were incorporated: one driven by a generator-powered pump, and another by an inverter-driven pump. The inverter-driven pump allows a “silent mode” where underwater noise is reduced, helping to avoid chasing fish away.

“The brief also called for a shelter deck between the forward wheelhouse and the net bin, to protect the crew and provide more working and storage space at wheelhouse roof level,” Stevens told Baird Maritime. “This had to be carefully designed so that it did not add to the enclosed volume and push the vessel over the 25GRT limit.

“By combining full live-bait capability with a compact under-25GRT platform, Tightline allows the owner to work in areas and at times where only larger, more expensive vessels would traditionally have been effective. She can catch and carry her own live bait, operate efficiently at range, and still benefit from lower manning costs and reduced overall operating expenses.”

Compared with older-generation vessels, Tightline offers increased fish hold capacity, improved crew comfort, and better seakeeping. This allows the owner to catch more per trip, operate safely in a wider range of weather conditions, and increase the number of workable fishing days per season.

“Her higher speed is a big benefit, roughly two knots faster in lightship [condition] and about four knots faster when fully loaded than previous boats of similar size,” Stevens remarked. “This speed translates into quicker turnarounds and more time on the fishing grounds while still returning to port in time to secure premium prices at the market. Overall, she fills the gap between small, limited-range boats and larger, more costly tuna vessels, giving the owner a very capable and economical fishing platform.”

The vessel is powered by a 280hp (210kW) main engine coupled to a Dong-I DMT140 reduction gearbox, driving a 900mm four-bladed, fixed-pitch propeller. The propeller is carried on a 70mm duplex 2205 stainless steel shaft fitted with a Tides Marine sealing arrangement. Stevens said this combination was selected for robustness, fuel efficiency, and ease of service in a demanding commercial environment.

The electronics suite is a comprehensive Furuno package, complemented by Icom and Hytera communications equipment. Navigation and fishfinding systems include a TZT13 multifunction plotters with 600W transducers, a Doppler radar for enhanced target detection, and an FCV295 echosounder with 1kW 50/200 kHz transducers. A satellite compass and a 711 autopilot are integrated into the navigation system, with a TimeZero software suite running on a marine fanless PC for advanced plotting and fishfinding functions.

For deeper fish location and tracking capability, Tightline is equipped with an CSH10 Omni omni-directional sonar, providing 360-degree coverage around the vessel. Communications are handled by Icom VHF radios, an Icom 804 HF set and Hytera/Kavikom units, giving the crew reliable voice and data links for both safety and operations.

According to Stevens, the omni-directional sonar gives the vessel a significant advantage in locating and following tuna schools around the boat, allowing for more efficient fishing and improving the chances of maintaining contact with fish over time. The integrated Furuno/TimeZero package meanwhile provides a modern, user-friendly bridge environment that is particularly well-suited to intensive tuna fishing operations.

The deck equipment includes a PETEC net power block for handling and stacking the live-bait purse net into the net bin on the main deck as well as a double warping-head winch with a one-ton line pull for net handling and other deck duties.

“The refrigeration system is a robust RSW setup that circulates refrigerant through stainless steel cooling coils installed in each of the fish tanks,” Stevens told Baird Maritime. “The system is designed to maintain tank temperatures at around minus five degrees Celsius for fresh fish in chilled seawater, minus 16 degrees Celsius for frozen fish in brine, and approximately minus 10 degrees Celsius in one of the tanks configured as a frozen bait hold.

"The combined system provides a high degree of flexibility in how the catch and bait are handled and stored."

Stevens added that for a vessel of this size, the deck and refrigeration package is relatively large and powerful, thus making the vessel particularly versatile.

“The 25hp (19kW) refrigeration plant is larger than on previous vessels in the series, specifically to reduce pull-down time and bring the tanks to operating temperature more quickly. This improves catch quality, reduces waiting times before loading, and allows the crew to adapt tank temperatures more rapidly as operational needs change between live bait, fresh fish and frozen product.”

Ample amenities for extended voyages along the coast

The accommodation layout placed the master’s berth in the wheelhouse along with a second berth above for the lead crewman, allowing both to be close to the controls and fishing operations and ensuring the master can be present and well-rested throughout the trip. There is also a dedicated head accessible from inside the wheelhouse for the master.

Below the wheelhouse is the forward accommodation space with two-tier bunks for 10 crewmembers. Aft of the wheelhouse, above the crew accommodation, are the galley and a separate head for the crew.

Immediately aft of the forward accommodation and forward of the machinery space are six insulated fish tanks with a total volume of approximately 38 cubic metres (8,400 gallons).

For Stevens, the greatest design challenge was accommodating all of the required equipment, systems and tank capacity within the very limited volume imposed by the under-25GRT rule.

“Maximising fish hold space while still providing adequate crew accommodation, machinery space and wheelhouse volume demanded a very smart and tightly integrated layout. At the same time, all machinery and systems had to be arranged for safe, efficient maintenance and short downtime, which is critical in a seasonal fishery.

“Major items include the hydraulic power pack, the 25hp RSW plant, an 80kVA genset, tuna spray pumps, the inverter-driven silent spray pump, bilge systems, multiple circulation pumps for chilled tank water, live-bait pumps and the Furuno OMNI CSH10 sonar. Ensuring good access, correct weight distribution and efficient routing of piping and cabling, all within such a compact envelope, required considerable design effort and careful 3D planning.”

Project success amid construction challenges

Stevens remarked that the main challenges in construction were the very tight build schedule and the impact of supply chain delays. The vessel had to be completed in just five months to be ready for the start of the new season, and he said this timeline was realistic for the yard in terms of fabrication and outfitting, though the late delivery of key machinery and equipment made the programme considerably more complex.

“In practice, we had to build much of the vessel ‘around’ outstanding components, leaving clear, pre-planned spaces and service routes based on supplier drawings rather than physically dry-fitting the actual equipment as it arrived,” he told Baird Maritime. “Once the delayed items finally came in, we had roughly four weeks to fit, connect and commission them. Keeping the project on schedule under those conditions was a major challenge and demanded close coordination between design, production and suppliers.”

Stevens said that because of the supply chain constraints, Sachal Shipyard was compelled to adopt a modified build methodology, sequencing work differently and relying even more heavily on upfront planning. Although he said it was initially challenging to implement, the company has since adapted this approach to subsequent builds and found clear benefits in terms of flexibility and schedule resilience.

“We have always been very CAD-driven as a yard, planning every aspect of the build in 3D to optimise structure, systems and layout,” said Stevens. “On this project, with critical items not physically available for much of the build, that approach became absolutely essential. We effectively built ‘blind’ from supplier drawings, and in the end, everything fitted into place as intended.

“That successful outcome reinforced our confidence in this methodology and has further entrenched detailed CAD modelling and production planning as core tools in our design office and on the shop floor.”