Knot Meter may or may not work

[Mike48]

We purchased our H23 last year. The PO told us that the knot meter would work off and on. The first 6 or so times out it work fine. Than it would work maybe 10 % of the time. I went under the boat and spun it and the wife said the needle moves. But when we got out on the water it was not working. Before we put it in this year, we would spin the paddle wheel and the and needle would seem to work fine. Again, when in the water it is not working. It is A SR Mariner Model #KM. Can anyone give me directions to what the problem may be.Thanks, Mike

 

[Gord May]

Tap Test

1) With power "on" to instrument, remove the coax cable from the BNC connector found on the rear of the speed instrument (display).Bend a paperclip into a U shape and place one end of the paperclip into the center hole of the BNC connector on the rear of the unit. With the other end of the paperclip tap on the outside of the same connector (essentially shorting the inside pin to the outside collar) rapidly while watching the display. If the speed increases as you tap then the instrument is capable of producing a speed, you should be able to see at least a 5 knot speed with rapid tapping. If not you will need to send the knot meter in for service. If this is ok, proceed to the next step.2) Re-connect the cable to the rear of the knot meter and locate the paddle-wheel speed sensor in the hull. Follow the cable back 10 feet and disconnect the cable at the junction. Perform the same tap test at the end of the cable leading to the knot meter by shorting the center pin to the outside shell, and have someone observe the reading on the knot meter. If you can produce a good reading on the knot meter then the inter connect cable is ok, and you will need to check the paddle wheel.