Replacement for Autohelm ST50 depth transducer?

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greenalien

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Just launched for the season, and after 20 years reliable service, my Autohelm ST50 depth meter is just flashing 0.0 - so I'm guessing the transducer has failed. As it's a through-hull fitting, there's no chance of easily pulling it out, so I'd like to just replace it with an in-hull transducer - I can't be the first person with this problem, any suggestions as to which transducer will work with the ST50 display?
 
I think in your position, I'd consider buying the Raymarine, (Airmar), transducer and make a temporary, in-hull arrangement using some glassed-in uPVC tube and oil for coupling.
For next season, assuming a lift-out, fit it properly.
 
Try Googling for Airmar---I think they make most transducers these days. There are quite a lot for sale on Ebay but I'm not sure which ones are compatible with the ST50.
 
You need a 200kHz transducer, something like an Airmar P19 (there's one of these on eBay now).
 
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greenalien said:
Just launched for the season, and after 20 years reliable service, my Autohelm ST50 depth meter is just flashing 0.0 - so I'm guessing the transducer has failed.
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I went through similar with a Stowe (rather older) a couple of years ago and after a lot of faffing about, trying to make sure I had diagnosed the right bit, it turned out to be a poor connector in the power supply. The supply voltage when the instrument was off was fine, but when switched on it dropped like a stone.
 
greenalien said:
Just launched for the season, and after 20 years reliable service, my Autohelm ST50 depth meter is just flashing 0.0 - so I'm guessing the transducer has failed. As it's a through-hull fitting, there's no chance of easily pulling it out, so I'd like to just replace it with an in-hull transducer - I can't be the first person with this problem, any suggestions as to which transducer will work with the ST50 display?
Click to expand...
If you go to Airmar.com, and find their reference pages, they will list all the transducers compatible (usually just the plug) with your equipment.
Depending on how your hull is constructed it should fire through it ok, though not quite as well as in the water. Testing with a plastic bag of water with the transducer in it and held against the hull is the usual test.
If you are lucky, you have a removable transducer, and can swap it over, but if you housing doesnt have a valve, that might be a bit risky/wet.
It might be worth just checking the connections and wiring on the old one to be sure.
 
Thanks for all the information - the current transducer is through-hull and epoxied in, so no easy removal - I'll check all the wiring, end to end, and if there's no visible fault I'll buy the recommended Airmar unit and try it in 'in hull' mode. I hear that a plastic bag full of Swarfega makes for good acoustic coupling! Luckily, my ancient 'flashing rotary LED' backup echosounder still works so I'm not totally 'blind'.
 
nigelmercier said:
It never ceases to amaze we what some people come up with.
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Old thread I know, please bear with me. Our ST50 thru hull transducer has started acting erratically -Sadler 34 with double skin. Wiring checked, all good, new display tried, same result. Original transducer is potentially glassed in (given the other lash ups we have found during refit) so could be a pig to beach and simply replace with a new one - it might be something that can’t be done over a tide. So… I would prefer an in-hull but can’t seem to find a compatible Airmar model, and even if I could, would it work through the double skin? If I get a replacement thru hull is the bag of swarfega (or summat else) solution actually likely to work through the double skin too or is the beaching option and risk it the only way ahead? Thoughts?
 
The transducer on my ST50 failed last year while the boat was in the water. Also the display unit was getting unreliable - too faded to be easily readable, and prone to resetting itself into feet rather than metres! So I bought an i50 triple pack (instrument, log, depth) to replace it. But I couldn't do the full job till the boat was out of the water, as the existing transducers were through-hulls.
It was suggested to me that the new (through hull) depth transducer would work fine if pushed firmly against the inside of the hull in a bed of ordinary frame sealant. And, to my sceptical surprise, it did!
I think the main thing is to make sure that there is no layer ,between the transducer face and the water, of something acoustically very different, so that the signal doesn't bounce straight back off a big impedance mismatch; i.e., make sure there's no air gaps. So you may get away with the double skin; or you may not, if the inner layer is very low density. There may also be a problem with attenuation if the layer between the skins is absorbent of sound. The only way to find out is to try it...
Good luck!
Steve
 
sgr143 said:
The transducer on my ST50 failed last year while the boat was in the water. Also the display unit was getting unreliable - too faded to be easily readable, and prone to resetting itself into feet rather than metres! So I bought an i50 triple pack (instrument, log, depth) to replace it. But I couldn't do the full job till the boat was out of the water, as the existing transducers were through-hulls.
It was suggested to me that the new (through hull) depth transducer would work fine if pushed firmly against the inside of the hull in a bed of ordinary frame sealant. And, to my sceptical surprise, it did!
I think the main thing is to make sure that there is no layer ,between the transducer face and the water, of something acoustically very different, so that the signal doesn't bounce straight back off a big impedance mismatch; i.e., make sure there's no air gaps. So you may get away with the double skin; or you may not, if the inner layer is very low density. There may also be a problem with attenuation if the layer between the skins is absorbent of sound. The only way to find out is to try it...
Good luck!
Steve
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Mmmm… either way the existing transducer is U/S, it’s just how we get over the hump until we can replace it. A temp bodge where I could fit one in a bag of goop until we can properly dry out and do it would be good. Can’t even do a harbour wall job in Falmouth next to the old Bosun’s locker anymore, the space seems to be full of liveaboards that are permanently moored there.
 
If you do find a replacement ST50 sensor (sadly mine was destroyed in cutting it out of the hull), it's a good idea to test it first by wiring it up to the instrument head, powering the instruments up, and then dangling the sensor into the water so the action end is just below the surface. If all is well, you should then get a sensible depth reading, and can proceed to fitting the sensor inside the hull with frame sealant / bag of gunk / raspberry jam etc.
 
My ST50 depth transducer failed last year - replaced it with this one from Cactus Marine in Plymouth - works perfectly with my ST50 instruments.

Raymarine Thru-hull Plastic Depth Transducer (p19) - 14m Cable (M78713-PZ)

Hudson Marine is amother useful supplier - their website is very helpful.

And I’ll second SGR143’s suggestion re testing - I did the same, wired up the new sensor through the hull aperture and placed the transducer in a bucket of water. By lifting it up and down in the water I could see the display changing
 
Also a big thumbs up to Hudson marine. I could have got the i50 gear a bit more cheaply at, say, Marine Superstore, but the pre-sale and after-sale support and advice I got from Hudson marine more than justified the slight extra expense. They really know their stuff.
 
KevinT1 said:
My ST50 depth transducer failed last year - replaced it with this one from Cactus Marine in Plymouth - works perfectly with my ST50 instruments.

Raymarine Thru-hull Plastic Depth Transducer (p19) - 14m Cable (M78713-PZ)

Hudson Marine is amother useful supplier - their website is very helpful.

And I’ll second SGR143’s suggestion re testing - I did the same, wired up the new sensor through the hull aperture and placed the transducer in a bucket of water. By lifting it up and down in the water I could see the display changing
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I believe the P19 is the very same model sold with the ST50 when it was originally released.

I've been looking into transducers recently, and it seems like Airmar (who make them) was originally part of Raymarine, which was originally the leisure division of defence conglomerate Raytheon. It wouldn't surprise me if there's a government contract requiring Airmar to maintain a supply these transducers decades into the future.
 
KompetentKrew said:
I believe the P19 is the very same model sold with the ST50 when it was originally released.

I've been looking into transducers recently, and it seems like Airmar (who make them) was originally part of Raymarine, which was originally the leisure division of defence conglomerate Raytheon. It wouldn't surprise me if there's a government contract requiring Airmar to maintain a supply these transducers decades into the future.
Click to expand...
Turned it on at 0400 this morning and it instantly read true. Checked it when light with a line and it was correct. Not a blip since then until half an hour ago now it’s flashing again and jumping about. Bleddy thing!!!!!!
 
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