ST50 Speed Problem

[Johncabot]

The Read-out marches up and down sometimes settling on the correct speed for a while. Say correct ~5kts Reading range ~2 to 25kts.

Need help with diagnosis.

[goboatingnow]

fouling of the paddlewheel transducer?

Dave

[Johncabot]

Thanks dave. No. I have carried out all known checks of the system.
I assume the head can count & therefor is receiving bad pulses from the wheel -- but need more assurance before replacing.

[Lake-Effect]

Originally Posted by Johncabot

The Read-out marches up and down sometimes settling on the correct speed for a while. Say correct ~5kts Reading range ~2 to 25kts.

Need help with diagnosis.

Bunch of questions:
- how often does this occur?
- what else is happening when it occurs? (sailing conditions, fast/slow, port or starboard heel... only when generator runs, etc)
- how old is the installation? How old are the instruments?

I'm thinking it's cabling or something to do with it (eg interference). I'd suggest first inspecting all connections between the transducer and the instrument, including the lugs at the instrument. Fix anything that seems iffy, loose or corroded.

[Johncabot]

Thank you. The problem is at all conditions. When it settles on the correct speed it will hold for 3 or 4 minutes. The unit is ~ 19 years old.
I am scrupulous in maintenance and store the read out off the boat in Winter. I believe you are correct about connections but there is only one at the read out. Gold plated and shiny clean. I think the transducer, needs replacement but I must pull the floor up plus much more to run the cable and wish to be sure it's worth it.

[Lake-Effect]

Originally Posted by Johncabot

I believe you are correct about connections but there is only one at the read out. Gold plated and shiny clean.

How about the crimped-on connectors? Do the crimps still seem solid, any looseness or visible corrosion in the crimp area? Maybe give them all a little squeeze with a crimp tool.

if you can borrow a known-good sensor, you can verify that the instrument is ok... hold the paddle wheel under a running tap.

Longshot... If you know someone with a portable oscilloscope, using one to look at the pulses at the instrument coming from your speed sensor would tell you alot about the sensor and the wire. You should see nice fat rectangular pulses all at the same levels, no jumping about, no skinny or soft pulses, no extraneous signals.