NorthStar Navigation EXPLORER 657 operation manual Bottom is not displayed

4-2 Bottom is not displayed:

aThe 657 may have Manual Range selected and the depth may be outside the range value selected. Either change the 657 to Auto Range or select another depth range (see section 8-5).

bThe depth may be outside the 657’s range. While in Auto Range, the display unit will display “--.-” to indicate that there is no bottom detected. A display of the bottom should reappear when in shallower water.

4-3 The bottom is displayed too far up the screen:

The 657 may have Manual Range selected and the selected Range value is too high for the depth. Either change the 657 to Auto Range or select another depth range (see section 8-5)

4-4 Bottom echo disappears or erratic digital reading while the boat is moving:

aEnsure the back of the bottom surface of the transducer is slightly lower than the front and the front is as deep in the water as possible in order to minimise the generation of bubbles through cavitation. (See the Transom Transducers Installation Guide, for more information.)

bThe transducer may be in turbulent water. Air bubbles in the water disrupt the echoes returned, interfering with the 657’s ability to find the bottom or other targets. This often happens when the boat is reversed. The transducer must be mounted in a smooth flow of water in order for the 657 to work at all boat speeds.

cElectrical noise from the boat’s motor can interfere with the 657. Try some suppression spark plugs.

4-5 There is a double bottom trace displayed:

aThe boat may be in an area that generates shadows (see section 8-2).

bIn shallow water, the echoes may bounce. Reduce the gain setting (see section 8-6) and/or reduce the sonar pulse power (see section 17-3).

cDecrease the Range.

Northstar Explorer 657 Installation and Operation Manual 89