Humminbird 363 manual Finding the Cause of Noise, Isolation, Boat’s engine, Cavitation from

Finding the Cause of Noise

Electrical noise usually affects the display with many black dots at high speeds, and high sensitivity readings. One or more of the following sources can cause noise or interference:

Possible Source of Noise	Isolation
Other electronic devices	Turn off any nearby electronic devices to see if the
	problem goes away, then turn them on one at a
	time to see if the noise re-appears.
The boat’s engine	To determine whether the boat’s engine is the
	source of the noise, increase the RPMs while the
	boat is in neutral and stationary to see if the noise
	increases proportionately; if noise appears when
	you rev the engine, the problem could be the
	spark plugs, alternator, or tachometer wiring.
	Replace the spark plugs with resistor plugs, install
	an alternator filter, or route the control head
	power and transducer cables away from the
	engine wiring.
Cavitation from the	Turbulence created by the propeller can cause
boat’s propeller	noise; make sure the transducer is mounted at
	least 15” (38 cm) from the propeller, and that the
	water flows smoothly over the face of the
	transducer at all times.

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