DESIGN ENGINEERING & PRELIMINARY TECHNICAL EVALUATION OF THREE ENTRANCE HEXAGONAL TRAP

Abstract

Entrance orientation, hydrodynamic loading, and bottom sliding are critical constraints in trap development. This study developed a three-entrance hexagonal trap, audited its component-level hydrodynamic resistance, evaluated sliding sensitivity under alternative bottom-contact assumptions, and conducted preliminary field trials. Prototype development was undertaken from December 2024 to February 2025 at “Balai Besar Penangkapan Ikan’s” workshop and at north of Semarang waters. The rigid hexagonal prism had 0.75 m sides and height, a maximum span of 1.50 m, an 8 mm steel frame, 2 inch polyethylene netting, a mass of 6 kg, and material costs of IDR 680,000. At a design current of 1.5 m s⁻¹, consistently recalculated drag was 26.73 N for the netting and 12.87 N for the frame, giving 39.60 N total drag; the netting contributed 67.5%. Depending on the assumed bottom coefficient (0.61-0.75), the sliding safety factor was 0.78-0.96 for the original mass and 0.97-1.20 after adding 1.5 kg of ballast. Catch was recorded in three of eight settings and comprised 31 unidentified individuals consisting of crabs and fish. The prototype was constructible and deployable, but the absence of a control trap, standardized soak time and bait, species and size identification, and near-bottom current measurements prevents conclusions about comparative catch efficiency, selectivity, and field stability. The design should therefore be regarded as a proof of concept requiring controlled experimental validation.

Key words: bottom stability, drag force, hexagonal trap, prototype design, three entrances