User manual RAYMARINE L750 FISHFINDER

[. . . ] Distributed by Any reference to Raytheon or RTN in this manual should be interpreted as Raymarine. The names Raytheon and RTN are owned by the Raytheon Company. L750 Fishfinder Operation Handbook Raymarine Contents i Contents Chapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 About the L750 Fishfinder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] This will continue until the unit can see the bottom again. Chapter 3: Operating Instructions 37 Before we explain the other basic pages, there are some general things you should know about the operation of the Fishfinder. Fish Indications Even using advanced sonar technology, it is sometimes hard to detect a fish in the water. The body of a fish is just a little more dense than the surrounding water. There is really nothing very solid for the sound waves to bounce off of. The L750 Fishfinder is very good at telling the difference between a fish and the surrounding water. Let's say that there are two fish of the same size: one is close to the surface, and the other is near the bottom. The fish which is close to An arch-shaped image indicates a fish. 50 kHz 200 kHz 50 kHz 200 kHz The same fish appears differently when shown by the 50 kHz or 200 kHz transducer beams. This is how the images appear when the "fish symbol" feature is turned on. This shows a fish detected in sidelooker mode. A fish moving under a stopped boat shows as a line. When the boat is moving very fast, a fish appears as two parallel lines. Fig. 3-4 Fish Indications 38 L750 Fishfinder: Installation and Operation Handbook the surface will have a larger arch. This is because the fish which is closer returns more of the sound waves back to the Fishfinder. Actually, the sound waves are usually reflected by the air sac near the center of the fish, and not by the body of the fish. A fish with a large air sac will produce a large fish arch, while a fish with a small sac will produce a small arch. The return from a fish will have a different appearance, depending on the frequency used. When using the narrower 200 kHz beam, the same fish will produce a narrower arch. If the boat is moving very fast, a fish may be indicated by a single vertical line. When the Fish Symbol feature is turned on a fish will be indicated by a fish-shaped symbol on the display. The symbol also indicates which of the two frequencies was used to locate the fish. If the fish was spotted by the wide 50 kHz beam, the symbol will appear to be hollow. If the fish was detected by the narrow 200 kHz beam, the symbol will be solid. Bottom Indications The bottom usually produces a strong echo, so it is easy for the Fishfinder to see a lot of detail. The Fishfinder can indicate many different kinds of bottom conditions. An uneven bottom which is covered with rocks or coral produces a complex display like that shown in Fig. The bottom image is irregular, with long "tails" pointing upward. [. . . ] In general, use a higher sensitivity setting for deep water, and a lower setting for shallow water. A level in the water where two areas of differing water temperature meet. Sometimes a thermocline can reflect sonar waves and present a false display. Kick-up bracket: Knot: LCD: Nautical mile: Port: PVDF: Range: Sensitivity: Starboard: Statute mile: Stern: Thermocline: Glossary 83 Transducer: Transom: White Line: A device which sends and receives high frequency sound waves through the water. This feature helps to show the difference between weak returns (including fish near the bottom) and strong returns (including the bottom itself). [. . . ]