Hi sblatt
I use a 798ci - great unit and works well in waters off Perth, Western Australia. I started with a 788 and at the time used the fish id feature - the software is supposed to 'interpret' the sonar repsonse of fishes. Most of the reading that I did on the subject suggested that this feature should be turned off by the user. The sonar response is a wide open inverted U shaped arch. The edges of the arch represent the entry and exit of the sonar beam across the fish - the central section of the arch is thickest representing the strongest return of the central part of the sonar beam. The shape and composition of the arch will vary greatly deending on boat speed, fish size and time that the fish spends in the sonar beam. Other responses include scattered spots or clumps that can represent baitfish schools (individual fish too small to generate arches).
I've attached a photo showing a reef ('bommie') and you'll notice some fish arches to the right - classic shape - there are also some smaller clumpy spots that probably represent small baitfish schools. Ive found other articles though that reckon you should turn the fish finding algorithm on (see attached) - I guess its a matter of trial and error. A couple of books that I found really useful both published in Australia by the Australian Fishing Network (AFN) are
1.) How to use depth sounders & GPS - Fred Studden - AFN - ISBN 9781 8651 3152 8
2.) Depth sounder secrets - Rick Huckstepp - AFB - ISBN 9781 8651 3103 0 - really great illustrated examples of interpreting sonar by a renowned fisherman.
Good luck with it all
Regards
Simon
How to use your sounder.pdf (516.3 kB - downloaded 350 times.)