Problem with Raymarine ST40 bidata transducer

[Frank Langer]

Hi,

The temperature reading on our Raymarine ST40 bidata instrument has started reading wrong--it reads at 12 degrees celcius when the actual water temperature is 9 degrees, and when left on the temperature reading increases steadily to about 25 degrees celcius, with the boat at the dock in 9 degree water.

I can only get answers from Raymarine Tech people by email, and they have written that the thermisor in the transducer provides the temperature reading by increasing/decreasing resistance based on temperature. The thermistor itself is not accessible, so they say I need to replace the transducer.

Does anyone know how easy or difficult this may be? I have removed the transducer and replaced it with the dummy plug while the boat is in the water, for cleaning purposes. The transducer wire is moulded into the transducer and disappears under the floor, emerging under the cockpit and is then led up the leg of the pedestal to the instrument, where it is connected with a slide on connection. I am thinking that a messenger line from the instrument pulled under the floor, and then pulling a new transducer cable through to the instrument again. Is that correct? Any better ideas?

I am debating just ignoring the temperature reading, but am a bit worried that if the thermistor has stopped working, perhaps the knotmetre is also on it's last legs, though the paddlewheel seems fine and it is currently reading accurately. The system was installed about ten years ago, but as everything else is working well, I'm hesitant to replace it; replacement is not cheap, so I don't want to do it if it isn't required.

Can anyone shed any light on this?

Thanks,
Frank

 

[Dan Morehouse]

Frank,
I have the identical instrument on two boats. Never had trouble with the water temp function, just the knotmeter. If they say the only fix is to replace the transducer, and the temp reading is important enough to you, it might be easier to splice the new cable to the existing one rather than run an entire new length. I had to splice mine because it wouldn't reach all the way to the binnacle from the transducer, and I believe they supplied connectors for making the splice. Might be worth asking them about.

Dan Morehouse
1981 E-38 "Next Exit"

 

[Frank Langer]

Thanks, Dan. A splice would be much easier than re-routing the cable. I think I can live without the temperature reading, as long as everything else continues to work properly (though it was nice to know water temp before I jumped in! )

Anyone else have any information about these units?

Thanks,
Frank