Topic: Relative Fish Size

[Capt. Shodamane]

Ok...so I have had my 998c for about 2 weeks now, and have taken it out on my home lake about 5 or 6 times so far. Everything works great! I fish for largemouth bass 99% of the time, and have been trying to locate schools of bass/bass in general, on my side imaging/down imaging sonar. I am seeing TONS of fish/baitfish on my sonar, but I can't quite figure out the "relative" size of the fish I am seeing. I started out with my SI range at 100 feet on both sides, (Doug Vahrenberg's video), but I can't seem to pick out larger gamefish yet. I have since reduced the SI range to 75 feet, and I still can't seem to easily locate 12"+ size fish. What is the easiest way to determine fish size on the side imaging screen? Theoretically, if I have my SI range set to 75 feet on both sides, should a 12"(or 1 foot) long fish stretch 75 times across each side? I'm assuming that fish between 12 and 24 inches should be fairly easy to spot on SI sonar, due to the pictures I have seen on the internet. I apologize for not posting pictures of the fish I am marking. I'll get some snapshots the next time I am out and post them for you guys to see the fish I am talking about. thanks-capt. shoda

[Humminbird_Greg]

Not trying to dissuade you here but it’s not that easy.  Most of the guys that can do this have a lot of experience in correlating the fish that they have caught with what they have seen on the Si sonar.

Some things to consider are that the amount of sonar returned to a transducer is affected by the species of fish, the amount of air in its air bladder at the time, the angle of the fish to the transducer and a whole host of water conditions.  All this means that the same fish could show up as a larger or smaller sonar return on the display of your unit.  The settings on your unit and even installation of the transducer affect this as well.  With the Si Range set at 75 feet you are using the 800 pixel wide display to show 150 feet.  This means that each pixel has to represent 2.25 inches (~0.19 feet).  Those pixels are pretty small to (with over a hundred per square inch).  The speed of the boat, whether the fish is stationary or moving with/opposite/away from the boat and the Chart Speed will also affect how a fish is shown in the sonar.

I guess what I am trying to say here is there are no shortcuts.  You will just have to put in the time on the water, catching fish, with the menu settings that you are comfortable with.

[W9GFO]

This means that each pixel has to represent 2.25 feet.

It is 2.25", not feet.

[Moose1am]

" sounds better than '   

[Humminbird_Greg]

Doh! 
Thanks guys, I went back and edited my response… that was my first day back after being out sick so if that is the only thing I messed up I was doing well!   

[Moose1am]

Thanks Greg.  I appreciate all that you do for us.  Just want you to know that.  And it's good that you corrected the mistake. We all make them.  But it takes a big man to admit a mistake and to take corrective actions.  You are That man!  I've learned a lot from you over the last few years.
I've noticed that my unit is showing the depth at 19ft deep when my older LCR 8000 Humminbird Unit is showing the depth to only be ten feet.  I never noticed the difference before. And I was on a flat not a drop off so that's telling me that the 898 C SI unit's shallow water depths are off or showing the water too deep.  At first I thought that the sound waves were bouncing off the hard bottom and back up and back down again.  That would give me the 18 ft reading vs 9 ft .  That still could be the problem .  I went to find the type of water so that I could chose saltwater but I could not find that option anymore.  I guess it's in another menu category.  But I've now decided to update the firmware and see if that make the unit read bettter and more accurate in shallow waters.   I need to find a SDHC chip that's empty before I can load the firmware on my unit. 
But if the unit's reading wrong in shallow water then I own Lake Master an appology as I've been critical of one of their IN maps of the lake I fish a lot.  I was complaining that the shallow water shelf that I fish a lot was not mapped accurately. It may have been that my Humminbird Unit was reading the shallow water area of the flat shelf as being much deeper. It never occured to me that the Unit was reading the shallow depths as being deeper than it was.  I'll have to do some more testing to figure out what's going on.

[Humminbird_Greg]

Moose,
Make sure it is not some sort of sonar interference from your LCR 8000 that is causing your 898c Si unit to pick out the wrong sonar reflection as the depth.

[Moose1am]

OK I'll check on that next time I'm out on the lake.