N.E.A.T.: A Torsion Spring System to Aid in Cutting and Removing Derelict Trawl Nets in the Papahānaumokuākea Marine National Monument
Creators: name: Sun, Laura
name: Chen, Vanessa
name: Walker, Colt
name: Tan, Nathan
Publisher: name: Stanford Digital Repository
Year: 2025
Subjects: subject: Mechanical engineering
subject: FOS: Mechanical engineering

description: Derelict fishing nets, commonly known as "ghost nets," constitute 46-70% of marine plastic pollution and pose severe threats to marine ecosystems, particularly in protected areas such as the Papahānaumokuākea Marine National Monument (PMNM). Trawl nets, a type of thick grid fishing net, constitute 80-90% of this derelict fishing gear and are often caught on coral reefs or tangled around wildlife, causing severe damage or even death. These trawl nets can weigh several hundred pounds when saturated with water, often necessitating that they be cut into smaller sections to allow for manageable lifting and removal from the ocean. The Papahānaumokuākea Marine Debris Project (PMDP) is a non-profit organization dedicated to cutting and removing these nets, but current methods rely on one diver manually tensioning the nets while another diver cuts with a serrated bread knife, a labor-intensive and inefficient process. To enhance the efficiency and ergonomics of net removal, we developed the Net Expander and Tensioner (N.E.A.T.), a torsion spring-loaded mechanical system that creates tension in a portion of a net bundle. N.E.A.T. is first actuated to the closed position by the user and inserted into the net. Once inserted, the compact device uses a double torsion spring pivot mechanism to automatically open the N.E.A.T. and apply continuous tension until a section of net is stretched. This tension is applied to the net through large fork-like prongs. N.E.A.T. facilitates more effective net cutting by removing the need for a second diver to manually hold and tension sections of the net, enabling one diver to conduct both the tensioning and cutting operations. The diver then uses the PMDP-preferred serrated bread knife to perform clean cuts. Once the cut is complete, the user closes N.E.A.T., removes it from the net, and then repeats the process as necessary. Experimental testing helped us verify that N.E.A.T. applies 59.43 pounds of force to the net when fully actuated, more than the 30 pounds of force required to easily cut the net. Pronged net interfaces arranged in a staggered formation enable both easy insertion and removal of the tool and fast net cutting – they also ensure compatibility with a variety of trawl net mesh sizes (0.5”- 4.5”), strand thicknesses (<¼”), and materials, representing the breadth of trawl nets encountered in real operating conditions. Ergonomic grips with long lever arm handles create a mechanically advantaged way to actuate the tool. Experimental testing verified that the user needs to apply only 15 pounds of force to close the tool, below the 25 pound threshold determined to be comfortable for repeated loading. Additionally, even when opening accidentally, N.E.A.T. accelerates at a maximum of 9g and applies a peak force of only 93N, below the calculated acceleration and force thresholds that cause concussions and bodily harm. N.E.A.T. is fully constructed out of corrosion-resistant materials, but the use of dissimilar metals leaves the system vulnerable to long-term galvanic corrosion. Comparative time trials confirmed that a single diver using N.E.A.T. could achieve faster net cutting than a two-diver manual operation. When counting cumulative time spent by both divers, a single diver with N.E.A.T. was able to achieve similar results 13.5 seconds faster, a decrease of 55.3%. By decreasing the time and physical effort required for net removal, N.E.A.T. has the potential to improve PMDP’s operational efficiency and reduce diver fatigue. Future work includes full fabrication of the tool in stainless steel, ergonomic and weight reduction optimizations, reduction of assembly complexity to decrease manufacturing cost, and fabrication of multiple units for simultaneous use by multiple PMDP dive crews.