In article ,
"LD" wrote:

OK, I see the differences but I'm unlikely to need a finder to look deeper
than 100' (in the Gulf of Mexico). Out of Pensacola, you have to go 15 to
20 miles out to get over 100' and I wouldn't do that very often in my 20'
runabout. SO, is a dual beam, 24/60deg for example, needed or useful at
these depths?
thanks, LD

Ok, now we have enough information to expound on the question at hand.

If you never expect to look below 100 Ft the a nice 200Khz
sounder/fishfinder will work great in your application. 200Khz will
give you excellent small target definition, and good target
discrimination, if you use a very narrow tranducer like maybe 12 degrees
or better.
Most of the small sounder outfits don't spec the transducer's beamwidth,
and just sell a generic transducer with an average 25 degree beamwidth.
This will work ok for most applications , but will tend to not provide
individual fish discrimination, that can be obtained with a narrower
beamwidth. Power output for depths of less than 100 Ft at 200 Khz
doesn't need to be more than 50 watts PEP. More will tend to fill the
area with reverberations that just fog up the return signals, and reduce
system clarity.

Bruce in alaska
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