Tiêu đề FO Unit 19 corrected.pdf ✅

UNIT:19 FISHING TECHNOLOGY Part I: Fishing Craft Technology Section 1: Principles of Fishing Vessel Design and Construction The design and construction of a fishing vessel are governed by a complex interplay of hydrodynamic principles, structural engineering, and the specific operational demands of the intended fishery. A vessel's ability to operate safely and efficiently is not an incidental characteristic but the direct result of a meticulous design process that prioritizes stability, seaworthiness, and fitness for purpose. 1.1 Fundamental Design Principles: Stability, Buoyancy, and Seaworthiness A fishing vessel's stability is its capacity to return to an upright position after being heeled over by external forces such as wind, waves, or the dynamic loads imposed by fishing operations. A vessel is considered "stable" when it possesses sufficient positive stability to counteract these forces and "unstable" when it does not, placing it at risk of capsizing. This critical characteristic is not static; it changes continuously throughout a voyage with every change in loading, sea state, or operational activity. The foundation of stability lies in the interaction between two primary forces: gravity and buoyancy. The total weight of the vessel—including its hull, machinery, fuel, catch, and gear—is considered to act downwards through a single point known as the Center of Gravity (G). Conversely, the upward force of the water that supports the vessel is concentrated at the Center of Buoyancy (B), which is the geometric center of the vessel's submerged volume. When a vessel is heeled, the shape of its submerged volume changes, causing the Center of Buoyancy (B) to shift to the low side. This shift creates a lever, known as the righting arm (RA), which is the horizontal distance between the vertical forces of G and B. The force generated by this lever is the righting moment, which acts to restore the vessel to its upright position. A key measure of a vessel's initial stability at small angles of heel is its metacentric height (GM), the distance between the Center of Gravity (G) and the metacenter (M), a point through which the force of buoyancy is considered to act. A larger GM indicates greater initial stability, resulting in a "stiff" vessel that rolls quickly. However, this subjective "feel" of a vessel is a dangerously incomplete and often misleading indicator of its overall safety. A vessel's ability to survive heavy weather is determined not by its initial stiffness but by its entire range of stability, which is graphically represented by the righting arm curve. This curve plots the righting arm at increasing angles of heel, and its total area represents the vessel's reserve energy to resist capsizing. Numerous operational factors, such as water trapped on deck, the lifting of heavy gear, or the accumulation of ice, can drastically reduce this reserve energy and the angle at which the vessel becomes unstable, often without significantly altering the