This doesn’t quite sound right
Speed of sound in water is around 1450-1500m/second
At a 30m range (60m flight of sound there and back)
ASSUMING no processing time and exactly the range (typically it is a bit over (say 35m in this example))
So about 0.04 seconds for the sound in the water
Thus around 25 pings per second
Anything above that you have multiple pings in the water column