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Depth reading wrong

ghostlymoron

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9 Apr 2005
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Most depth instruments are sonic so you should be able to hear them clicking. If not, the sensor or wiring is faulty. Any chance of borrowing one you know works and trying it?
 

laika

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Most depth instruments are sonic so you should be able to hear them clicking. If not, the sensor or wiring is faulty. Any chance of borrowing one you know works and trying it?
it’s clicking. I’ve tried wiggling all the wiring to no avail. No chance of borrowing another unfortunately.

cost of an in hull ,even if I throw it away later, is probably less than a haul out
 

Daydream believer

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I glassed in a 50m Osma plastic straight connector just in front of the keel inside a locker centrally. I used west resin & filler to make it oil tight.
I fitted a blanking plug socket to that with a screwed plug. The parts were bought off the shelf at Travis Perkins but could probably be bought from Screwfix, B & Q etc.
I drilled a hole in the screwed plug to take the threaded part of the transducer & passed the wire etc through the hole. I clamped the transducer to the cap with a nut above & below the screwed cap. I adjusted it such that the end of the transducer came within 1mm of the hull. I filled the unit with oil & screwed the plug with transducer in place.
It worked perfectly Ok. No mastic etc.
If the OP did this he could use it for the rest of the season then move the transducer to the hull ( if he still wants to) when the boat is out of the water as there is no damage to the unit. The cost of the plastic components was about £ 12-00 from memory & I have left mine in place for future emergency.
 

laika

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Speaking to Hudson marine, they’ve suggested siliconing a through-hull to the hull (no fancy liquid bath) as a temporary measure. Apparently should work, and if it doesn’t it’s because the hull’s too thick and an in hull wouldn’t have worked anyway. Anyone done this?
 

steve123

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12 Nov 2001
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75
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Yorkshire
When I started using a solar panel, which I move around the deck, I found that the depth readings were sometimes too low and erratic but returned to normal when the panel was disconnected. I think the wiring for the panel runs close to the depth sounder wiring - I had someone fit it for me.
 

oldmanofthehills

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Not much use on a yacht doing 6 kts approaching a steep sand bank. Especially to a single hander
The lead weigh needs to be hefty if the boat is moving at all. The weight is initially used to tell if you are approaching the shallows, when near you slow down.

I like my sounders but have used lead line when sounders gave nonsense reading, but only when nervously entering shallow harbours or crossing shallow grounds - the problem there was muddy boundary layer gining apparent 1.5m depth when chart suggested 5m and about to deepen. It was near 5m as my 4m lead didnt touch, and then it deepened and normal reading restarted
 

Daydream believer

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The lead weigh needs to be hefty if the boat is moving at all. The weight is initially used to tell if you are approaching the shallows, when near you slow down.
I like my sounders but have used lead line when sounders gave nonsense reading, but only when nervously entering shallow harbours or crossing shallow grounds - the problem there was muddy boundary layer gining apparent 1.5m depth when chart suggested 5m and about to deepen. It was near 5m as my 4m lead didnt touch, and then it deepened and normal reading restarted
If it is that muddy then one might as well, just touch the mud. I often do when entering Bradwell marina & the like; but always motoring & not when close hauled cutting the corner of a sand bank at 5 kts. A weight that is too heavy, on a thin line just cuts one's hand. A thick line catches the water flow.
 

oldmanofthehills

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If it is that muddy then one might as well, just touch the mud. I often do when entering Bradwell marina & the like; but always motoring & not when close hauled cutting the corner of a sand bank at 5 kts. A weight that is too heavy, on a thin line just cuts one's hand. A thick line catches the water flow.
Not a good idea to touch mud banks in the mid Bristol Channel. Getting stuck is fine but when that 14m tide comes in at 3 to 5kts it can tumble you on your side. Even anchoring to try and avoid being pushed onto higher ground, is tricky as one boat at pulled under by the 1st severn bridge about 25 years ago, and another needed rescue. However it can save miles and even save a tide sneaking across some bank. Oh and the banks shift on a 19 year cycle.

Routes across exist near high tide but study of the depth is vital. 5 boats from our club got stuck on a bank in the sheltered water of cardiff bay, due to poor advice from penarth marina. They told us to keep lock dead astern but that route actualy hit the highest spot. Many years later it now has the outer wrack buoy on it

My lead line is in fact an 8 piece of gas pipe on 2.5mm cord. Not that heavy or long. Ther final probing finger not the main nav tool
 

laika

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2 marine electronics people:
#1: it’s very probably the transducer. Eventually they get water in them which changes the frequencies and you get the variable results you describe
#2: it’s definitely the head unit. If it was the transducer it wouldn’t be clicking. Your only option is to get a new head unit from eBay.

For a variety of reasons I was unconvinced by #2. I’m going to order the replacement transducer and go with silicone (as suggested by #1), or failing that the arrangement daydream believer kindly explained in so much detail.

Having said that…I do have an arduino and a laptop on board. Does anyone have a pointer to documentation on what the head unit sends and receives? Might be good to eliminate the head unit as the problem
 

laika

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Update: new transducer arrived. Dangled it in the water, stuck the wires into the head unit….and it read 1.5m. So Either I made a wiring mistake or marine electronics person #2 was the winner. So this makes the question of “does anyone have a pointer to how the head unit interprets the transducer signal?” Even more pertinent.

Lucky I saved myself several hundred quod in not hauling the boat out.
 

vas

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21 Jun 2011
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Volos-Athens
interesting, I'd go for buggered transducer as well...
No idea is my answer to your question. I guess you have made sure the connections at the back of the head unit are nice and clean. don't even know how the cables connect there.
 

vas

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do you know if transducer is sending NMEA0183 sentences to the head unit? if so, an old pc with hyperterminal would help. Doubt it's the case though
 

pvb

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do you know if transducer is sending NMEA0183 sentences to the head unit? if so, an old pc with hyperterminal would help. Doubt it's the case though
It's just a simple analogue signal, not a smart transducer.
 

vas

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It's just a simple analogue signal, not a smart transducer.
so a high pulse or something every x milis that are then converted in the head unit to depth? wont be great fun finding how that works with an arduino me thinks
 

laika

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so a high pulse or something every x milis that are then converted in the head unit to depth? wont be great fun finding how that works with an arduino me thinks
Yes. Given that several manufacturers make units to interpret the signal and they’ve been around for years I’m hoping the info might be available. I’ll try asking airmar if no one knows how these things work…
 
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