From: ed.mccrudden@rose.com (ed mccrudden)
Subject: What fish finder
Organization: Rose Media Inc, Toronto, Ontario.
Date: Wed, 23 Dec 1992 13:13:58 GMT
X-Gated-By: Usenet <==> RoseMail Gateway (v1.70)


Date Entered: 12-10-92 16:58
In article: <1992Dec10.090230.20722@ncrcae.ColumbiaSC.NCR.COM>
kevin@turbo.Columbia.NCR.COM (Kevin Ormerod) writes:

KO>If you really want to see fish you can't beat an X-16 or alternatively
KO>the lower cost Eagle Mach-1.

That's for sure.  These are both paper units.  Liquid crystal sonars
are toys.

However..... the X-16 seems like overkill for fishing in twenty feet
of water.

You don't need power in twenty feet of water, and peak-to-peak power
isn't a true measure of a unit's capability.  RMS power is what counts.
But when the water is that shallow, you can only use a fraction of the
available power anyway.  You have to turn the gain way down.

I would suggest that the reason it's so hard for ANY sonar to mark
fish in twenty feet of water is because of the size of the cone at
such depths.  You can't see fish unless they are in the cone, and
twenty feet down the cone isn't very big.

Therefore, for shallow water, the most important factor is cone angle.
A wide-angle transducer will help more than extra wattage.

KE>And BTY, don't expect to see the nice fish arches that you see in the
KE>glossy ads.  At least not very often.  The only time that you see an arch
KE>is when conditions are perfect.  Usually gamefish show up as scratches.

This depends on what you are doing.  My Mach-1 makes those nice textbook
arches every day, all summer long, but I am fishing over a lot of water
and a lot of fish (Lake Ontario).

We often mark hundreds of "hooks" down 120 feet, but we don't set the
lines down there.  We don't mark many fish at the thirty foot level,
but we CATCH lots of them there, which proves that they are indeed there.

The reason again is cone angle.  In order to mark a fish at thirty feet,
the fish has to swim directly under the boat, and this applies whether
you are fishing over 300 feet of water or 35 feet of water.   A hundred
feet down, the sonar cone is maybe thirty or forty feet wide, and you
can see a lot of fish.

It helps to think of sonar as being similar to a flashlight beam.  Take
a mini Mag-lite and hold it over a table in a darkened room.  Imagine the
flashlight is your transducer and the table is the lake bottom.  Adjust the
beam as tight as you can get it, and note the size of the spot it produces
on the table.  Now raise the flashlight a couple of feet higher above the
table and see the spot expand.  The angle of the cone of light is the
same, but the coverage is increased because the source is farther away
from the target.  This illustrates the difference between shallow and
deep water for a fixed cone angle.

Now lower the light back to where you started and adjust the beam until
it is nice and wide.  You can get the same coverage as you had when you
raised the light....without raising it.  Now raise it above the table
like you did before, and you'll see the edges of the cone get dim.
You have just demonstrated the effect of installing a wider angled
cone (transducer).  The intensity of the light (the equivalent of a
sonar's wattage) is the same in both cases, but opening up the cone
angle dramatically improves the flashlight's ability to light up the
table when you're holding it down low.  When you move it away, the
light gets weaker.

The 20 degree transducers that come with the Mach-1 or the X-16 are no
good for shallow water.  Even if you could fire their entire 200 watts
RMS into the water (you can't), you'd only be looking at a two foot
circle down there.  You need a 45 degree (or wider) transducer.

-Ed
<ed.mccrudden@rose.com>      In Toronto, where it's snowing like hell.
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