Just got a Garmin 73 CV. Since all images are showing what has already been passed over, at 3mph how far behind the boat is the item I see? I want to use my new unit with precision for deep brush piles and objects. Thoughts and help anyone...

3 minutes ago, Bartableman7 said:

Just got a Garmin 73 CV. Since all images are showing what has already been passed over, at 3mph how far behind the boat is the item I see? I want to use my new unit with precision for deep brush piles and objects. Thoughts and help anyone...

Are you sure it only shows what you pass over? I thought it send out a signal in kind of a 360 cone, and the deeper the water, the farther down signal goes and thus, the wider the cone.

I haven't used the unit you have but it should allow you create a waypoint on anything you see on the graph.  Then just use the GPS to go to that waypoint.  It should do all the math for you.  The manual should show you how to do this.

6 minutes ago, Tennessee Boy said:

I haven't used the unit you have but it should allow you create a waypoint on anything you see on the graph.  Then just use the GPS to go to that waypoint.  It should do all the math for you.  The manual should show you how to do this.

This is exactly what I do on my Lowrance units. Mark the exact brush pile or whatever target it is. 

3mph = 4.4 ft/sec.

 

 

Doesn't sonar travel at the speed of sound in water?

 

Call it 1480 meters/second in round numbers, so 4,855 feet per second.  Call it 0.006 seconds in 30 feet of water, at the above 3 MPH and 4.4 fps, that's put the return back in just a hair more than 5/16 of an inch of boat movement.

 

...so unless you're in really deep water, the return is pretty much instantaneous.

 

...after that, it's kind of a function of chart speed...

If going 3mph (4.4ft/sec) and you pass over a stump, in one second it will be 4.4' behimd you. In two seconds it will be 8.8' behind you......and so on

18 minutes ago, Comfortably Numb said:

If going 3mph (4.4ft/sec) and you pass over a stump, in one second it will be 4.4' behimd you. In two seconds it will be 8.8' behind you......and so on

not technically behind you but behind the transducer depending on where it is located when it grabs the image.

Everything displayed is a history of what your transducer has passed over or by, nothing is displayed real time scrolled on a sonar screen.

If the TD is stern mounted the target is always behind you.

Tom

With the exception of Garmin LiveScope.

 

SE Kansas grass grower

On 6/18/2018 at 1:06 PM, Tennessee Boy said:

I haven't used the unit you have but it should allow you create a waypoint on anything you see on the graph.  Then just use the GPS to go to that waypoint.  It should do all the math for you.  The manual should show you how to do this.

I also do this with my Garmin 73SV.  When you pass over the structure you want to mark you can use the D-pad buttons to move the cursor to the structure on the graph and I forget what button you push (I think it may be MARK or SELECT?) and it will mark a waypoint on your map.  Then you can circle around and you'll know where that structure is by watching the map.