Nasa Target log - erratic readings

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jneale

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This year my Nasa log has gone crazy. It first started registering only 1/2 the boat speed. Impeller is clean and spins easily with a puff. Recently it shows anything from 88 knots down to 30, upto 56.5, zero and all over the place. Impeller is clean. bottom is cleanish (some light slime - no obvious interruptions). power and cable connections good.
Echo sounder transducer and wiring are close to the log bits, but it always used to be ok

Anyone any ideas ?:confused:
 
Ours did the half speed thing. Solved by replacing the impeller. As I recall there are two magnets in the impeller and eventually one will corrode it's way out of the plastic and fall off - hence half the speed.

However this doesn't help with the 88 Knots issue.That sounds more like a loose connection or damaged wiring causing lots of short 'pulses' to the display that might look like high speeds, and sometimes no signal that would look like zero knots. I'd check the cable run and connection at the display end.
 
ianhandel said:
Ours did the half speed thing. Solved by replacing the impeller. As I recall there are two magnets in the impeller and eventually one will corrode it's way out of the plastic and fall off - hence half the speed.

However this doesn't help with the 88 Knots issue.That sounds more like a loose connection or damaged wiring causing lots of short 'pulses' to the display that might look like high speeds, and sometimes no signal that would look like zero knots. I'd check the cable run and connection at the display end.
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Second that. Had exactly the same problem recently. Check impeller. Cheap to replace.
 
I've done without mine since one of the magnets fell off years ago.Don't know why I bothered with installing it in the first place.
 
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