11-07-2005, 02:13 PM
Hey smallmouth89,
OK leaving the mathmatics of it out, let's look at your situation as you posted it.
Of course I don't know how you have your transducer mounted nor what kind of tube you have(next time describe your set up to me so I can tell more about what is happening). A number of things could be at play here. For example, if you are in a belly boat, you could be seeing your fins on the fish finder or your jig could show up as a fish if it is directly under the transducer(given the size of the jig or the sensitivity setting you are using). Also, I don't remember off hand if your Max 20 has Real Time Sonar(RTS). In any case, remember that when you use the Fish ID option(the fish icons) the readings are actually produced from an algorithym of the sonar returns from both frequencies and displayed as what is interpreted by that software as a possible fish sonar return.
You see a fish icon register at 3 feet while you are in 15 feet of water. The 3 feet depth is measured from the bottom of your transducer - not the surface of the water(unless the Max 20 has an offset adjustment like mine). When the fish registered at 3 feet(assuming a solid icon), that means it passed through a beam directly under the transducer that was about 1 foot in diameter. If the icon scrolled off the screen, that means the fish moved out of the cone(on your fishfinder, while using the fish icons, I don't think it indicates the direction the fish moved - mine does). If the icon was hollow, that means it passed through a cone(the lower frequency) of about 3 feet in diameter under the transducer, but just off to one side(could be in front or behind as well) of the 1 foot cone that is produced by the higher frequency.
You can tell the direction of the fish if you are just reading the raw sonar data and not the fish icons(it's the shape of the arch that tells you the information about the encounter - the thickness of the arch tells you something about the size of the fish). If you are moving and the fish is moving with you, you will see a straight line on your screen. The same thing will happen if you are stationary and the fish is holding directly under you. Your jig will also do the same thing - show up as a straight line across your display - moving your jig up and down will show up as an up and down zig zag line.
Sensitivity - If you increase the sensitivity, you will read more weaker sonar returns(smaller fish). If you decrease the sensitivity you will read fewer sonar returns(only the larger fish will appear). Check your manual to see if the adjustments for sensitivity can be done for each frequency individually.
Again, I dont remember if your finder has a surface clutter adjustment or noise filter, but if it does, decreasing those adjustments will remove some of the algea or interference from aeration, turbulence or even the thermocline readings - increasing the adjustment will do the opposite - allowing you to identify more baitfish and or debris in the water.
I don't know if I explained that very well - let me know.
[signature]
OK leaving the mathmatics of it out, let's look at your situation as you posted it.
Of course I don't know how you have your transducer mounted nor what kind of tube you have(next time describe your set up to me so I can tell more about what is happening). A number of things could be at play here. For example, if you are in a belly boat, you could be seeing your fins on the fish finder or your jig could show up as a fish if it is directly under the transducer(given the size of the jig or the sensitivity setting you are using). Also, I don't remember off hand if your Max 20 has Real Time Sonar(RTS). In any case, remember that when you use the Fish ID option(the fish icons) the readings are actually produced from an algorithym of the sonar returns from both frequencies and displayed as what is interpreted by that software as a possible fish sonar return.
You see a fish icon register at 3 feet while you are in 15 feet of water. The 3 feet depth is measured from the bottom of your transducer - not the surface of the water(unless the Max 20 has an offset adjustment like mine). When the fish registered at 3 feet(assuming a solid icon), that means it passed through a beam directly under the transducer that was about 1 foot in diameter. If the icon scrolled off the screen, that means the fish moved out of the cone(on your fishfinder, while using the fish icons, I don't think it indicates the direction the fish moved - mine does). If the icon was hollow, that means it passed through a cone(the lower frequency) of about 3 feet in diameter under the transducer, but just off to one side(could be in front or behind as well) of the 1 foot cone that is produced by the higher frequency.
You can tell the direction of the fish if you are just reading the raw sonar data and not the fish icons(it's the shape of the arch that tells you the information about the encounter - the thickness of the arch tells you something about the size of the fish). If you are moving and the fish is moving with you, you will see a straight line on your screen. The same thing will happen if you are stationary and the fish is holding directly under you. Your jig will also do the same thing - show up as a straight line across your display - moving your jig up and down will show up as an up and down zig zag line.
Sensitivity - If you increase the sensitivity, you will read more weaker sonar returns(smaller fish). If you decrease the sensitivity you will read fewer sonar returns(only the larger fish will appear). Check your manual to see if the adjustments for sensitivity can be done for each frequency individually.
Again, I dont remember if your finder has a surface clutter adjustment or noise filter, but if it does, decreasing those adjustments will remove some of the algea or interference from aeration, turbulence or even the thermocline readings - increasing the adjustment will do the opposite - allowing you to identify more baitfish and or debris in the water.
I don't know if I explained that very well - let me know.
[signature]