Fish Finder Questions

[fishindrew]

I have a Lowrance HDS-5X. the question I have is how to determine where you are in relation to the bottom. I asked the sales person at Bass Pro, he said that the right side of the screen is directly under the boat...makes sense to me. I was fishing at my local lake this weekend and was looking at the fish finder for structure, once I saw something come on to the screen I would through a marker buoy.after fishing around the marker buoy for a while I would pick up and go somewhere else. Wile picking up the buoy i would notice that the structure that I thought i was fishing was not there. I guess the real question is if the screen on the display is always moving (even when the boat is stopped) how can you figure out how far back you actually ran over the structure. Thanks for all your help in advance.

[Carrington]

there is a slight delay in the time that you run over the stuff and the sonar picks it up.  i usually throw my buoys a good 3-5 feet behind the boat when i see something

[Wayne P.]

There is no "slight delay".

When the sonar pulse cone picks up a return, it is displayed instantly on the first vertical row of pixels on the right side of the display. That return will stay on the display until it scrolls off the left side of the display as history. The distance from the transducer of that return and the actual location can vary according to depth, screen scroll speed and boat speed.

The longer you wait after a return is first displayed to throw out a marker, the further away from it you may be.

If the return doesn't repeat itself on the right side of the display, the return is not within the coverage of the sonar pulse cone and can be off to either side of the boat travel by many feet according to the amount of coverage the unit/transducer has at that depth.

Depending on the depth, the outside perimeter of the sonar pulse cone is not directly under the boat and can be many feet away. Any return within that cone coverage is displayed and can the in any direction.

Another thing to consider is the actual bottom coverage your unit has. The rated cone angle is at a certain strength in decibles. The actual coverage in lesser strengths can be a lot more and usually is.

[Carrington]

the delay is the time that it takes the signal to leave the transducer, hit the bottom, go back to the transducer, and then finally appear on the screen.

[Wayne P.]

That "delay" is a very small fraction of a second. I guess that you know that sound travels about 4 times faster in water than air.

Sound in air is 1125 feet per second.

Sound in water is about 4856 feet per second.

The rate that each sound pulse is transmitted (ping rate) changes automatically or is manually adjustable. The only "delay" involved in the ping rate is the time it takes for the pulse to be transmitted and received before the next ping is transmitted.

[J Francho]

the delay is the time that it takes the signal to leave the transducer, hit the bottom, go back to the transducer, and then finally appear on the screen.

LOL, you arguing over milliseconds?   :

[fishindrew]

Thanks for the help guys. I will  have to go out for a few days and play with it. I will print the post and take with me next time as a reference.

[Carrington]

im not arguing over a millisecond, im just stating what i have noticed from my hummingbird, usually my unit will show the stuff once im like 1-2 feet past it.

[Ima Bass Ninja]

Wouldn't it also depend on where the transducer is mounted? If its mounted on the trolling motor what you see on the screen will most likely be under the boat and if its mounted on the transom then what you see is most likely behind you correct?

[CWB]

Boat speed would play a factor in where you toss a marker. If you see something running fast, turn around and idle over the area until you pinpoint it and if it really looks good, drop the trolling motor and mark it using the bowmount unit.

[J Francho]

im not arguing over a millisecond, im just stating what i have noticed from my hummingbird, usually my unit will show the stuff once im like 1-2 feet past it.

If your unit has RTS, turn it on. 

[Hot Rod]

To expand upon what Wayne and JF said, that first row of information at the right of our graph or "RTS" is similar to the old flasher units and is the most accurate in real time.  I utilize that feature when I am fishing over/for deep suspended fish to locate my bait in relation to the fish/cover. 

You need to understand what the graph is actually reading.

Remember the cone is covering in 3D but it only shows on your screen in 2D.  What shows on the screen is a return relative to the transducer.  That return could be dead center in the cone or off to one edge.  If it is off to one edge of the cone the return will show up deeper (i.e. farther away from the transducer) than it actually is in the water column.  Only when something is straight under the transducer will it show up at the exact depth it is in the water column.

For example take a fish arch.  The reason it shows as an arch and not a dot is that when the sonar first detects the fish it is farther away so it shows up on your screen as a "deeper" and weaker return.   Approaching and passing over the fish the return is closer and stronger so it shows thicker and "shallower" on your screen.  Then as the transducer passes the fish the return is weaker and farther. Fading until it is completely outside of the cones detection.  So the arch turns down, thins out and dissipates.

A fish arch may show up covering several fee of depth on your screen.   It doesn't mean the fish is several feet long or thick.  Its just showing the relationship between the transducer to the fish as it passes.

Hope that helps.  It is a difficult concept to convey and understand.

[Wayne P.]

Good explaination Hot Rod.

On the Lowrance web site there is a tutorial about understanding sonar and the fish archs are described.

The right side of this image is the RTS (Real Time Sonar)

[Carrington]

ive never seen an rts feature on my hummingbird.

[J Francho]

Here it is on a HB unit, the strip to the right.  If you can read a flasher, its very similar:

[Carrington]

the lag i was talking about is in si and i have never seen that bar in si.  i do have that bar for my conventional unit up front.

[J Francho]

Why would you use SI to see what is under the boat? That was the original question, right?

Learn how to see your bait, the fish and the fish taking your bait, using the RTS bar. Very useful for deep water fishing.

[Wayne P.]

The same applies to SI/DI except with Imaging the sonar pulse is a thin beam front to back and from the surface to the bottom on each side. The lenght of time the sonar beam is on a return is a lot less.

Still the very first horizontal row of pixels is the only real time return and all below that is history.

How far a return is from the transducer depends on the screen scroll speed and the boat speed.

A recorded return is still about instant with no perceptable lag. Any "lag" is the scroll speed which makes no difference except the length of time that history is on the display.

[Carrington]

i ususally set the scroll speed to be the same as the boat speed in mph.  and i have di up with si so i can see below my boat.

[Wayne P.]

Matching the screen scroll speed with the boat speed for SI and DI is a good setting.

You can see directly below the boat with the SI view. That is the water column part of SI.

I use DI to interpret what 2D is showing.