Fishfinder Confusion!

[OntarioFishingGuy]

Sorry if this is confusing, but i just got into fishfinders, and i am quite confused. when i look at the screen of a standard fishfinder (Humminbird 570) i don't where the things i am seeing on the screen are. Are they in front of the boat, behind the boat, under the boat, on Mars, etc.Any help would be greatly appreciated.

 

Thanks

[FishinCop646]

Typically behind the transducer with that model. How far depends on the depth because of how the sonar cones out.

[OntarioFishingGuy]

I think i understand... but when i see the bottom, is that a cross section of the bottom behind the transducer?

[FishinCop646]

Get on youtube and search reading a fishfinder. They can explain far better than I can!

[slonezp]

The stronger the return, the closer to the boat. I'm guessing you have a black and white unit. The darker the shading the stronger the return meaning the fish are under the boat. The lighter the shading means the fish are off to the sides or further away from the boat. As far as bottom composition, a hard thin black line is a hard bottom. The thicker the line, the softer the bottom. Weeds and grass will appear differently but you should be able to tell their relation to the bottom. If the unit is color, on the right side of the graph is your color palate. The colors appearing at the top of the palate=the strong return(similar to the black on the B&W unit). The colors at the bottom of the palate=weak returns(similar to the shades of grey on the B&W unit). The cone spreads out further the deeper the water. The diameter of the bottom of the cone could equal the depth of the water ie. 15fow=15ft diameter or could equal 50% of the depth ie 15fow=7.5ft diameter. It depends on the unit specs.  

[FishinCop646]

Well put Slonezp!

[OntarioFishingGuy]

Thanks a lot for your help, i really appreciate it.

[slonezp]

Here's a good video. A lot won't apply to your unit but the basics are all the same

[Ratherbfishing]

On a 2D sonar I always assumed the transducer would in the top middle of the screen-since sound moves out in all directions in an approximate cone shape from all sides of the tranducer.  And as I understand it, a bright red signal could be a hard object on the edge of the cone and not just directly under the transducer-unlike what the narrator of the video says.  Am I wrong in this?

[FishinCop646]

The objects that you see show up on the right edge of the screen as you go over them. By the time you pass them they are in the middle of the screen. In relation to your image the transducer would be in the top right corner. As for the hard object it could be on the edge of the cone.

[slonezp]

On a 2D sonar I always assumed the transducer would in the top middle of the screen-since sound moves out in all directions in an approximate cone shape from all sides of the tranducer.  And as I understand it, a bright red signal could be a hard object on the edge of the cone and not just directly under the transducer-unlike what the narrator of the video says.  Am I wrong in this?

He was using that as an example to describe the way the cone spreads from the transducer. I can understand how that could be mistaken, The current returns are on the right. as they scroll left, they become history if you are moving. If you are sitting stationary, you can vertical jig and watch your bait in relation to the fish.

[Ratherbfishing]

 In relation to your image the transducer would be in the top right corner.

 

I'm really not trying to be argumentative (contrary perhaps but not argumentative) but if this were true, wouldn't that mean the screen depicts only that which the transducer has already passed directly over?  It's not a half cone (sliced down the center), is it?

[FishinCop646]

Your depth really becomes a factor. If you are looking at the bottom of 300 feet you could be looking at something in front of your boat. Keep in mind the more shallow the water, the smaller the cone. Typically, yeah, the graph depicts objects we have passed over.

[Wayne P.]

I'm really not trying to be argumentative (contrary perhaps but not argumentative) but if this were true, wouldn't that mean the screen depicts only that which the transducer has already passed directly over?  It's not a half cone (sliced down the center), is it?

The display is not a video monitor and the transducer is not a video camera.

The only real time subjects displayed are on the very first vertical row of screen pixels on the far right. Everything to the left of that first row is HISTORY.

If a display is 640 pixels wide, the first vertical row of pixels is 1/640th of the screen width.

 

That first row of pixels shows everything within the somewhat inverted cone coverage of the sonar pulse.

It a subjest is not repeated on that first row, it is not within the coverage of the sonar pulse.

 

There is no partial cone involved at any point.