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20 degree cone angle allows you to see more of the underwater world.
In 15 feet (5 meters) of water the 20 degree cone covers an area about
six feet (2 meters) across. The 8 degree transducer covers only about a
two foot (less than 1 meter) circle.
The 20 degree transducer is almost always the best to use in fresh
water, the 8 degree mostly in salt water. In a deep water environment,
(300 feet/100meters - fresh water, 100 feet/30 meters - salt water) the
narrow cone angle is more desirable. Since the sound energy is con-
centrated in a smaller area, it can penetrate to much deeper depths.
Both 8 degree and 20 degree transducers give accurate bottom read-
ings, even though the bottom signal is much wider on the 20 degree
model. This is because you are seeing more of the bottom. Remember,
the shallow edge of the signal shows you the true depth. The rest of the
signal tells you whether you are over rocks, mud, etc.
SIGNAL INTERPRETATION
Your SupraPro I.D. gives an accurate picture of the bottom that your
boat is passing. A bottom of firm sand, gravel, shell, or hard clay returns
a fairly wide signal. If the automatic mode is off and the signal narrows
down, then it means that you have moved over a mud bottom. Mud
absorbs the sound wave and returns a weak signal.
Turn up the
sensitivity to see a better bottom signal. Big rocks or stumps on a
smooth bottom send back signals above the bottom level signal. The
height of the signal depends on the target's height. As you pass over a
post, it should be clearly visible as a short line extending above the
bottom signal.
A steep slope returns a wide signal, the steeper the wider. Signals
returned from a high underwater cliff are usually the widest of all.
WATER TEMPERATURE AND THERMOCLINES
Water temperature has an important-if not controlling-influence upon the
activities of all fish. Fish are cold blooded and their bodies are always
the temperature of the surrounding water.
During the winter, colder
water slows down their metabolism. At this time, they need about a
fourth as much food as they consume in the summer.
Most fish don't spawn unless the water temperature is within rather
narrow limits. A surface temperature meter helps identify the desired
surface water spawning temperatures for various species. Trout can't
survive in streams that get too warm. Bass and other fish eventually die
out when stocked in lakes that remain too cold during the summer.
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