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Sea currents and temps can really mess with your Depth sounder.

Occasionally we all see it, we are sailing along, in very deep water, so deep the depth sounder has given up trying to measure and just shows “—“, then suddenly it reads 4m deep!!!!!!

Sailing you get used to this and explain it away any way you want, dolphins under the boat? whale? or more likely just a cold patch of sea water.

Temperature and current affects the sonar wave as it passes through the water the same way your voice goes higher when you inhale helium. The software in the sounder compensates for this but when its a sudden cold patch it struggles and you get an errant reading.

This was extremely highlighted for me the other day passing through the Messina Strait, where there are extremely volatile currents, upwells, cold and warm mixing seas (Tyrrhenian and Ionian seas) and even fast and slow moving currents right up to the surface.

The first to go was my forward looking sonar which simple refused to give anything meaningful as a reading and actually needed resetting before it would show reasonable data outside the straits it had got the computer so confused.

But even the depth sounder, randomly showed depths that were obviously (one hopes) incorrect.

All was well again once we had exited the straits and were in one sea with less current or more predictable currents should we say.

When you’re trying to whistle and someone throws in some helium… you’re gonna go up a pitch. Not the Depth sounders problem, just its challenge.

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