Join Date: Sep 2003
Location: Auckland New Zealand
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For me it's a fish finder
And I'm not big on fishing
When there is a need for knowing the depth, a depth sounder can do just that. And no more.
A fish finder provides a whole range of info like the shape of the bottom and the make-up of the sea bed (rock, sand, etc). Many of the better ones have forward-looking sonar that is also very useful.
And it can also see fish if that's of any value to you.