Airmar Triducer issues

[LittleSister]

I have an elderly airmar triducer (B744VL), connected to an ST40 speed/sea temp instrument and an ST40 depth instrument.

The depth is fine, but the speed permanently reads zero, while the temp readout is random. The instrument head seems fine, because I replaced it (longer story) and it made no difference.

The paddlewheel turns OK, and though I haven't yet had a meter across the leads to check that's working (there's a guide to doing this online somewhere), the fact that the temp also doesn't work leads me to suspect that's there's a wider issue. Perhaps there's some connection that's common to the speed and temp, but not depth.

Any ideas?

A replacement triducer of the relevant type is about £400, and while I don't need to know my waterspeed that much, it would be nice to have it working.

 

[jwilson]

Very common problem with Airmars and ST60s, I assume it's the same with ST40. Temp sensor dies and unit won't show speed. Fix is to disconnect temp wires and put about a 10Kohm resistor across the water temp wires input to the instrument. Speed will probably then work perfectly: seawater temp though will show up as fixed - mine shows always at 27 degrees C. As virtually the only navigational use for water temperature is off the US coast to establish whether you are in the Gulf Stream or not, non-working temperature is not a big deal for most people.

 

[LittleSister]

Thanks very much, jwilson. I recall reading stuff about the temp sensor resistance, but hadn't realised it affected the speed sensor. I will give it a go.

A reading of 27 degrees sounds great: I can pretend I'm in sunnier climes. I think l the last time I switched past the temp reading it was something like -41 degrees! Perhaps I could fit a potentiometer instead of a fixed resistor, and set the temp to suit my mood.

 

[Ningaloo]

My experiences in the Baltic lead me to believe that the Scandinavians would rather know water temperature than boat speed! Personally I use the water temperature to tell me if I'll survive a swim. 17C is my minimum for a brief splash but 18+ is more realistic to swim.
I've been without boat speed for a month or two due to fouling of the impeller. Losing this also stuffs up true wind calculations so it's definitely worth fixing, especially if you can get away without a £400 replacement.

 

[LittleSister]

Losing this also stuffs up true wind calculations so it's definitely worth fixing, especially if you can get away without a £400 replacement.

If replacing the transducer also magically gave me wind instrumentation (quadrucer?), I'd splash the £400. Otherwise I'll have to manage with wet finger in the air for wind direction, and how hard I have to hang on to my hat for wind speed!