Thread: Sonar Quiz #25

I believe the 2D cone is wider than the DI. the fish was on a slope and the 2D is level with the first spot it hits. I think this one goes to ShortGrub.

I think there are 2 possibilities.....Wilbur is close with the affect of the steep slope.......In the 2d return bottom indication is very thick and the fish can get lost in this thick bottom return.....The 2D is seeing a greater range of depth returns because it is getting returns from the front of the cone as well as the back of the cone on the drop.
The DI isn't affected as much because it is very thin front to back and won't be affected as much by the slope.

The other possibility is that the fish is further off to the side and not in the 2D cone......The Di is wider than the 2D

I can visualize this, but not sure if I stated it coherently.

Originally Posted by BobB

I think there are 2 possibilities.....Wilbur is close with the affect of the steep slope.......In the 2d return bottom indication is very thick and the fish can get lost in this thick bottom return.....The 2D is seeing a greater range of depth returns because it is getting returns from the front of the cone as well as the back of the cone on the drop.
The DI isn't affected as much because it is very thin front to back and won't be affected as much by the slope.

The other possibility is that the fish is further off to the side and not in the 2D cone......The Di is wider than the 2D

I can visualize this, but not sure if I stated it coherently.

IMHO ... that's possible, but would depend on which kHz setting was used by the 2d and/or DI.

A 20deg 2d cone angle will only show a bottom circle reading of a diameter that's 1/3 the depth ... whereas a 60deg cone angle will show a diameter that equal to the depth. The DI "angles" are 75deg for 455kHz and 45deg for 800kHz ... so if the DI was using 455kHz, the angle of the fan shaped sonar ping would cover 1.25 times the depth and an 800kHz setting would cover 3/4 the depth.

... cp

I'm confused about the depth. The 2D is showing 11.7 ft & the DI is showing approximately 18 ft.

Someone please explain

11.7' is going to be the closest bottom return......The would be the depth of the front of the 2D cone if going up a steep slope. If you look closely at the red section below the bottom return, that represents the "range" of depth the 2D is seeing. The boom of that red section is probably the same as the DI depth.

Originally Posted by BobB

11.7' is going to be the closest bottom return......The would be the depth of the front of the 2D cone if going up a steep slope. If you look closely at the red section below the bottom return, that represents the "range" of depth the 2D is seeing. The boom of that red section is probably the same as the DI depth.

BobB, got it....Thanks...Had a memory loss there for a minute...75 years working on me....

Originally Posted by Don G

BobB, got it....Thanks...Had a memory loss there for a minute...75 years working on me....

My problem is that I think I understand it, but can't explain what I am thinking.....The words just get lost now days.....Good thing for spell check too. I used to be a great speller when young, but now am lucky if I can spell if.

Originally Posted by wilbur

I believe the 2D cone is wider than the DI. the fish was on a slope and the 2D is level with the first spot it hits. I think this one goes to ShortGrub.

So if there were a flat bottom, same fish, but no quick rise of the bottom .would those fish show on the 2d? Have you ever heard anyone say that 2d won't lie? If it's down there,2d will show it? Does 2d have a blind spot in some cases?