ST50 depth not reading correctly

[ProDave]

So onto the next on the list of things not working as they should.

We have an Autohelm ST50 display connected to log and depth sensors. Nothing else. Log works as expected, but not the depth.

The unit displays a depth reading but it is flashing and rarely changes. The manual says that is a cabling fault. I am not so sure.

Before we launched the boat we anti fouled it, and did not notice the depth sensor. We painted round the paddlewheel but did not see the depth sensor, so it was probably already antifouled and we just added more. Would that be a reason for it not working?

If so we could go and dry out at low tide and clean it off to see if that revives it. If there is no hope of that being a fix, I won't waste the time. I am not brave enough to try pulling it while afloat.

 

[philwebb]

Before you dry out check that you haven’t got the airmar type depth sensor which can be epoxied inside the hull.
This is the type that I have, however my depth instrument is ST60. If you have this type of sensor you should check where the cables are joined as this is where corrosion can occur.

 

[ProDave]

I have not checked, but I was led to believe (from the manual) that the sensors came with a very long (about 40 feet) cable with the plug moulded on the other end to plug into the display. That explains the big coil of cable stuffed under the floor. So I was not expecting an in line connection. I have not checked that coil of cable, it could be damaged.

Looking under the forward locker I see what look like two through hull fittings so I don't think it is epoxied to the hull.

 

[earlybird]

Two particular places to examine are:- i) where the cable exits the tranducer, under the locker, look for damage, and ii) the round plug into the rear of the display.
The plug might be difficult to access but it's worth giving it a wriggle in case of corroded pins.

 

[neil_s]

I think the depth sensor cable enters the back of the display with two blade type connectors. Check here for corrosion or bad connection.

 

[ProDave]

Picking this up again, only just got around to having another look.

I have followed the cables, they appear to be a pre made cable assembly, way longer than needed, with the spare cable for each sensor coiled up under the floor. The plugs that plug into the display are pre made on the end of the cables. No obvious damage. Both connectors unmade and re made in the hope of wiping the contacts, no obvious corrosion and still the depth is not working.

So here is a picture of the 2 sensors from the inside.



The right hand one that can be removed from the inside I suspect is the paddlewheel log sensor.

In which case the left hand one is the depth sensor? It does not look like it can be pulled from the inside and I can't tell from that if it even goes through the hull of if it is just epoxied on the inside and works through the hull? If it can work through the thickness of the hull then I doubt a few coats of antifoul will be the problem?

Any thoughts please?

 

[Roberto]

I have the same st50 depth transducer, over the years it has been covered by a zillion coats of antifouling and always worked correctly.
Sorry cannot be of further help.

 

[jlavery]

Internal sensors rely on either a contiguous join between the sensor and the hull, or sit in a bath of liquid to provide sound conduction.

If the former, does it look like it's got any gap between the unit and the hull, or it's worked loose?

If the latter, it should be possible to remove the sensor from the housing, and adding almost any liquid (I've used water or olive oil in the past) in the mounting fixes it.

From the picture, looks like yours isn't in a liquid bath - so what does the join between the unit and the hull look like?

By the way, these units are usually designed to work with a specific cable length - don't be tempted to cut them! That's probably why there's a lot of coiled cable.

 

[ProDave]

That's why I posted the picture because I can't tell how it is mounted and if it is through hull or glued to the inside of the hull. Both fittings appear essentially the same from the inside and clearly the paddlewheel is through hull.

I don't want to go trying to unstick it from the the hull and then find it is through hull and have water coming in. This might be an over winter job now when on the hard. I have still not ruled out drying out on the drying pad to have a look from outside and then I might be happy trying to unstick it.

To me from the inside it looks like the workings of the sensor are at the bottom of a short tube and some kind of hard black compound poured it and set leaving just the cable coming out. I don't see any way to add fluid to fill a gap.

Does anyone have the install instructions for this sensor, at least it would tell us what glue to stick it to the hull with if it does come unstuck while investigating.

 

[earlybird]

From the picture, I'd say that your depth transducer is a through-hull type. With the boat out of the water, you would see it as a raised flange about 2" in diameter. The backing nut is visible inside the boat. The hard black compound that you refer to is potting compound, used by the manufacturer to seal the actual transducer into the mounting tube, thus forming an integral unit. Not something that you can remove.
A rather crude test of the system can be made if a portable radio with an am band is operated in the boat. If a regular click is heard around once per second, then the instrument is at least producing pulses.

 

[jlavery]

From the picture, I'd say that your depth transducer is a through-hull type. With the boat out of the water, you would see it as a raised flange about 2" in diameter. The backing nut is visible inside the boat. The hard black compound that you refer to is potting compound, used by the manufacturer to seal the actual transducer into the mounting tube, thus forming an integral unit. Not something that you can remove.
A rather crude test of the system can be made if a portable radio with an am band is operated in the boat. If a regular click is heard around once per second, then the instrument is at least producing pulses.

Hadn't spotted the backing nut - yes, looks through-hull.

 

[ProDave]

So almost back to the original question, are the through hull versions still able to operate with multiple layers of anti foul covering them. So many layers that when we antifouled the boat before launching her, we were not aware of the second transducer next to the paddlewheel.