Raymarine ST60 knotmeter

[DuncanMcMillan]

Water Temp and VMG still showing on display but no boat speed available. Paddle wheel seems ok. Pulling boat for bottom paint next week. Unit is nearly 9 years old so maybe it's tired.............no real way to test it? Has anyone replaced one of these? The removal and replacement is easy..........just the wiring part

[R.B.]

Here is something I had in my notes that may help:

Testing the Paddle Wheel Transducer

Testing the Speed Sensor:

• Verify that the transducer’s paddle wheel is free of marine growth and rotates freely on its shaft
• Power down the instrument
• Disconnect the GREEN and SHIELD transducer leads from the instrument display or instrument pod.
• Connect a multimeter to the GREEN and SHIELD transducer leads and configure the multimeter to measure continuity or resistance.
• Slowly rotate the transducer paddle wheel by hand. Note that as the paddlewheel is rotated, the multimeter should alternate between an open circuit and a closed circuit with each quarter turn. As such one complete revolution of the paddle wheel should open and close the circuit four times.

Should the multimeter respond as indicated above, then the speed sensor element of the transducer would be deemed functional. If not, then the transducer has failed and should be replaced.

Testing the Temperature Sensor:

The temperature sensor employs a thermistor as its sensing element. The impedance through a thermistor will change as the thermister temperature changes. Increases in temperature will cause a decrease in impedance through the thermister. Correspondingly, decreases in temperature will cause an increase in impedance through the thermister.

Example: If the thermister is immersed in water is 77 degrees F, the multimeter will report an impedance of approximately 10,000 Ohms. If the thermister is immersed in water is 68 degrees F, the multimeter will report an impedance of approximately 12,495 Ohms.

Other examples:

81 degrees F = 9,164 Ohms
77 degrees F = 10,000 Ohms
68 degrees F = 12,495 Ohms
61 degrees F = 15,004 Ohms
57 degrees F = 16,470 Ohms
54 degrees F = 18,098 Ohms
50 degrees F = 19,911 Ohms

It is not possible to directly test the thermistor. Testing is performed indirectly by applying a known resistance to the BROWN and WHITE terminals of the instrument display or instrument pod and noting the temperature reported by the instrument display.

Testing is performed as follows:
• Power down the instrument
• Disconnect the BROWN and WHITE transducer leads from the instrument display or pod.
• Install a 10,000 Ohm resistor across the BROWN and WHITE terminals of the instrument display or instrument pod
• Power on the instrument
• The display should report a temperature of approximately 77 degrees F.

Should the display respond as indicated above, then the thermistor has failed and should be replaced. If not, then the instrument display or instrument pod has failed and should be serviced by Raymarine’s Factory Repair Center.

[DuncanMcMillan]

Thanks Ralph. Time to get my orange CSI glasses on and get to the bottom of this. Much appreciated.

[vegasandre]

I just replaced the airmar transducer for 60 bux. Not worth doing all that testing. I just sliced the wires at transducer box and spliced the nee one in. Now my speed and temperture work great ten minute fix

[DuncanMcMillan]

Thanks Andre, when I looked at this morning I was wondering if I could do something like that or if I couldn't how could I access at pedestal without miniature doll hands............ running the cable was not an attractive proposition.
After I pulled the transducer out and got the bung in to replace it was clear that the paddle was well blocked with mussels, sea hair and other living organisms. The old toothbrush and some CLR got it clean and with a few flicks it was reading speed and max speed. It's hard to check with only one person and bad knees. What I really needed was a cell phone mount so that I could record the display.
I'll keep it out until after the bottom painting(they painted it last time) but I think it should be good. Thanks again.