I have a Raymarine ST40 Bidata speed/depth system on my yacht that was only installed within the past 2 years and suddenly the speed is not registering. The transducer is an Airmar thru hull model. It also has a temp function that operates off the same transducer as the speed (depth is a seperate transducer) and the temp function is still working fine.
I have checked the entire length of the cable from the transducer to the display for any breakes/cuts, checked all connections and checked that the little paddle wheel is not fouled and is spinning freely. Can't find anything to explain the sudden failure of the speed reading (one weekend it was working a couple later is was not). It's as if whatever within the unit registers the spinning of the paddle wheel is no longer picking up the signal.
I am wondering if anybody else has had similar experiences with these transducers? Is it fixable or am I up for a replacement transducer? Also if anybody has any suggestions for getting it functioning I would love to hear them, I am fresh out of ideas.

Thanks Ramona,
I emailed the transducer manufacturer and got a similar response about connecting a multimeter to the cables and seeing if it registered so I will give that a go and see what happens.
Hope it is not the bidata unit, I imagine that would cost more to replace/have repaird than the transducer. We will see.

I don't known the unit, but before you do anything
you have to establish what is really faulty.
i guess it is newish type of pick up, if not you tell me, I get back to you.
New pick up has build in "HALL" sensor.
that means you have 3 wires.
Plus-minus and pulses.
/hall sensor is normally open collector that's means/
you should measure 2 pluses against one minus.
When you move wheel one wire go low-high, if you move very-very slowly
even normal voltmeter will pick it up.
Probably not easy is get access to wires.
What you find here tell us which unit is faulty.
happy testing, based on your findings we continue.

cisco said...

There are not many people who I have spoken with in the last couple of years who bother with a paddle wheel speed/log sensor type log any more.

The reliability of GPS units is fairly well established and what is of most relevance to navigation is Speed/Course over ground.

The speed log has become more of a "Fun Gauge" until it breaks down at which time it becomes an outdated piece of marine electronics junk.

Be that as it may with GPS units being reliable read outs for SoG and CoG, I would never trust one more than my compass for course and steering readings.

Were I buying a second hand yacht and the seller was making a big point on the sale price about the fancy marine electronics fitted, I would ask the seller what it cost and upon his price quotation would say, "Well take your marine electronics off the boat and reduce your price by that amount and I will consider the boat then."

Second hand marine electronics are not worth much, if anything.

My advice is to forget about repairing the unit and just using it as a sounder until that part of it packs up, then ditching it and buying latest and new.

You can buy a pretty reasonable sounder these days for less than $200.

That's all well and good but if you have done any sort of racing in any sort of current you would understand the importance on speed through the water.

And the sounders you are talking for that price come with a transom mount transducer. Usually it is a minimum of $300 on top of the sounder for a through hull and for some small units they are just not available at all.

Yes GPS's are great as a log for cruising and motor boats but as a trimmer, if I was asked to do a regatta on a 30ft+ racing yacht with no water speed it would make life very hard!!!

I have to agree with Cisco, I find the GPS excellent, COG & SOG is all I need, to me, any more info is irrelevant. Also I am tired of having to install and remove the transducer every time I head out, also the growth on the paddle wheel is quite amazing after just a few days in brine.

Mat I say that this site is excellent as we all have our own point of view and there is nothing better than getting every ones opinion, they will always differ, what works for one does not necessary work for others.

To MatM14, I hope you sort out your problem from the good advice given.

Hi MatM, I have just been through all this hassle with raymarine ST40's. There is a bit of info on the net through Raymarine / Airmar, but to save you some trouble here is some info, also you can check out the magnetism of the paddlewheel, I couldn't get readings as per test and put a new transducer in purchased through BIAS at Belmont N.S.W. it came overnight cost around $150 (give or take a few bucks) + courier, and the unit is now fine.
I hope this helps,
Cheers, Dave.
RAYMARINE TRANSDUCER TESTING

Here are the testing procedures from Ray's website.

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.

Hi guys
35 years ago I build home made log. I used glass enclosed switch. Can't believe,
they are still in use.
Electronic shop still have them - this is description

Dry Reed Switch, Small No sliding parts ensure a virtually unlimited mechanical life. Vacuum Glass Enclosed---Low voltage applications < 24.0V---

What about that, now is best part current availability - yes
cost $ 0.30
Jaycar shop -
GLASS REED SWITCH - N.O.
Ideal for burglar alarms.Normally open, but closed when near magnet.Total length 44mmGlass length 16mm.. cost $1.95

Now is it REED SWITCH or depleted magnet?
You dare to go ahead: drill the reed switch or magnet, re-solder it,
epoxy or silicon back, distance is critical,
closer to surface better...... enjoy ...