Topic: 998 fish location in cone

[hannibal mike]

In Missouri we have a snagging season for paddlefish (spoonbill) that requires luck or accurate sonar location.  These fish are 4-6' long (35-100+ lbs), but rarely show on my side image (30-50' depth).  The down image does well, but I wonder how to tell their location (rt/left) within the cone when 30' down.  Also,  wonder if using the 800 setting to widen the cone might help  locate fish as the si has not helped me.  The si is fine for bottom contours/structure and perhaps I am not reading the image (on the water) as effectively as possible.  I would think that fish this size would present a large image, though I do understand that the program has some sort of normalizing system. 

[PaulB]

This is an image of a 14 ft Basking Shark taken with my 798 in 50-55ft of water, I was kind of expecting it to fill half the screen but it has given me a better idea of what to expect from fish on the SI.


It is a bit strange you're getting an image on the down imaging and not SI, I thought the DI was just a combination of the SI images but I'm sure somebody with more knowledge can confirm that?  I know that DI and SI have seperate sensitivity/contrast settings and that I've had to ramp up sensitivity even in 50-100 ft of water, I normally use sensitivity in the 16-18 range.  The best thing I ever did was use the recording feature and then playback on the actual device and tweak the sensitivity/contrast when looking at known fish, I've now got it so SI/DI shows inidividual fish in the 4-5lb range, they are only a few pixels long but you can see them.

[hannibal mike]

I think your idea of recording and tweaking is good, but these fish are usually migrating upstream and locations will be changed by my return.  They are migrating in the river (Mississippi/Sac/Osage) and the spring flow carries silt, leaves, and limbs.  All this makes it tough to use the higher sensitivity settings.  Thanks for your ideas and I am still curious how to determine the fish location within the cone when they appear on the screen.

[rnvinc]

Because 2d and DI do not differentiate left and right...or front and rear... the only target position info that can be gained from either is "distance from the Xducer"...(usually down but still within the beam shape)..

SI, on the other hand, can show distance from the Xducer (by activating the 4way cursor and placing it on the target), left and right, and approximate depth of target (by discerning the placement of the target's shadow against the bottom detail)...

Rickie

[Humminbird_Greg]

Paul B you are correct in that the Di sonar on the Si units is coming from the Si sonar beams.  If it is showing on the Di sonar than it is there in the Si sonar.  The reason that someone may not be able to see it is due to the menu settings and their expectations of what they think they should be seeing (like your Basking Shark).  Sensitivity has been discussed but what has not been mentioned is the range that is being shown.  The range used for the Di sonar is the same used for the 2D sonar and the water depth affects it (if running in the Auto setting).  The range shown on the Si sonar View/Window is set by the user.  If something is seen in the Di sonar with the range set to show 40 feet of water (distance) than the same thing would be shown at half the size if the Si range was set to show 80 feet of distance.  Usually the Si range is set much higher than what the Di range is set to.

Where in the Si sonar beam that Basking Shark is (or any other sonar return) cannot be easily determined while on the boat unless you guestimate it due to the sonar shadow it created.  It must have been pretty close to being under the boat though as you can see that the left Si sonar also had some data in it as well.  I’m gonna guess within 15 feet of being straight under the transducer?

BTW: I’ve seen others post images of spoonbill paddlefish, so I know that the units can show them.  I just can’t remember who or where they were posted…

[hannibal mike]

Good Point!  Had the Si on 65' each side, but could shorten and have improved visual.  These spring river conditions are a challenge.  There are paddlefish views posted (probably).   I better go practice, thanks.