Originally Posted by mad_machine
there any reason to keep the speedometre in this day and age of GPS?
Speed over water is different from speed over ground. If you sail in areas where there are a lot of currents it is useful to have both pieces of information so you know how much current you have with or against you. In our waters being aware of such things can get you to your destination faster.
As for the "tuning fork" I have never seen the like! Maybe it is supposed to align the flow with the knotmeter transducer?