If I understand you correctly the boat is on the hard. Sounders do not work well out of the water, you need the water to properly transmit sound waves.
You will not normally hear the pinging only a clicking sound if you are close enough to the sender unit( in the boat).
If the boat is in the water check unit at known depth( such as in marina at the dock) measure with stick and verify readings. Also remember thermoclines will sometimes cause erratic readings.
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“I'm not afraid of storms, for I'm learning how to sail my ship.”
Louisa May Alcott