In operation, an electrical impulse from a transmitter is converted into a sound wave by an underwater transducer, called a hydrophone, and sent into the water. When the wave strikes something such as a fish, it is reflected back and displays size, composition, and shape of the object. The exact extent of what can be discerned depends on the frequency and power of the pulse transmitted. Knowing the speed of the wave in the water, the distance to the object that reflected the wave can be determined. The speed of sound through the water column depends on the temperature, salinity and pressure (depth). This is approximately c = 1404.85 + 4.618T - 0.0523T2 + 1.25S + 0.017D (where c = sound speed (m/s), T = temperature (degrees Celsius), S = salinity (per mille) and D = depth). Typical values used by commercial fish finders are 4921 ft/s (1500 m/s) in seawater and 4800 ft/s (1463 m/s) in freshwater.
The use of the hook in angling is descended, historically, from what would today be called a "gorge". The word "gorge", in this context, comes from an archaic word meaning "throat". Gorges were used by ancient peoples to capture fish. A gorge was a long, thin piece of bone or stone attached by its midpoint to a thin line. The gorge would be fixed with a bait so that it would rest parallel to the lay of the line. When a fish swallowed the bait, a tug on the line caused the gorge to orient itself at right angles to the line, thereby sticking in the fish's gullet.
It’s often been said that the act of fishing isn’t actually about catching a fish. Rather, it’s about a quiet moment with nature and a chance to sit, think and relax, whether on your bass fishing boat or on the banks of a river. Of course, if you’re a sport fisherman reeling in that prize monster on a white-capped ocean, there isn’t much relaxation to be had. If you prefer ice fishing or fly fishing, shop eBay for everything you need for a day on the water. We have the right gear for you, regardless of whether your allegiance lies with Orvis, Shimano or Abu Garcia.
Important parameters of a fishing line are its breaking strength and its diameter (thicker, sturdier lines are more visible to fish). Factors that may determine what line an angler chooses for a given fishing environment include breaking strength, diameter,castability, buoyancy, stretch, color, knot strength, UV resistance, limpness, abrasion resistance, and visibility.