Humminbird GR16 manual Finding the Cause of Noise, Boat’s engine, Propeller

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 pro-
	portionately; 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 boat’s	Turbulence created by the propeller can cause noise;
propeller	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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