The final point to remember when you are looking out for fish arches is that it doesn’t need to be a full arch. Half arches (like the ones shown in the screen shot above) also show that there is fish. In ourtutorial on how sonars work, we explain in detail why sometimes you get a full arch and sometimes you get a half arch. The short answer is that you will get a full arch if a fish swims through the whole of your sonar cone, and a half or partial arch if they only swim through part of it.

Thru-hull: This means a threaded bronze, nylon or stainless steel shaft passes through the bottom surface of the hull. You have several styles to choose from: external football-shaped head with water flow smoothed by a fairing block that also corrects for the dead rise (sideways slope of the hull); or round mushroom head thru-hulls, either semi-flush or flush mounted. These are the most challenging to install, but likely to provide the best signal quality. Displacement power and sailboats generally use thru-hulls.
A fishfinder or sounder (Australia) is an instrument used to locate fish underwater by detecting reflected pulses of sound energy, as in sonar. A modern fishfinder displays measurements of reflected sound on a graphical display, allowing an operator to interpret information to locate schools of fish, underwater debris, and the bottom of body of water. Fishfinder instruments are used both by sport and commercial fishermen. Modern electronics allows a high degree of integration between the fishfinder system, marine radar, compass and GPS navigation systems.

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The thickness of the line representing the bottom is also a great clue to bottom hardness. Here the rule is simple – the thicker the line, the harder the bottom. But, be careful – sonar sensitivity can affect how thick the line is. The Deeper display has adjustable sensitivity. So if you turn up the sensitivity to 100%, the bottom line may appear thicker, if you turn it down to 10% it may appear thinner. So practice adjusting the sensitivity and get used to judging how much the bottom thickness varies based on this.
While catching a fish is often a case of matching wits—and great patience—a fisherman is at a distinct disadvantage without the right gear. eBay stocks the fishing supplies you need, like spinning rods, casting rods and more by St. Croix, Shimano and other top brands. There are plenty of saltwater and freshwater choices, so it doesn’t matter if you’re after salmon, trout or marlin.