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Airmar UST800/850 ultrasonic speed sensor - accuracy issues.


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This speed sensor seems to have a mind of it's own. I can calibrate the display to get it to agree with the GPS but then it's wrong high or low by 5-7% the next time out. I have averaged out the tidal effects using reciprocal courses when calibrating. The thing seems like a random number generator. 

I've asked our diver to be sure the sensor is well cleaned.

Sad that such an expensive sensor would give bs numbers.

Your experience?

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There are a lot of complaints about them, it seems you either get a good one or a bad one. The CS4500 in my boat has worked well for 11 years. 

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I had one that came with my boat, worked great for a couple weeks then all of the sudden hardly ever worked.  Went back to the time tested, old school paddle wheel and haven't had a problem since.  Nothing more frustrating than having thousands of dollars in boat electronics made completely worthless by one malfunctioning sensor.  Like DDW mentioned, some people never have any problems and swear by them, others have many problems. Seems like a great idea in theory and I was really excited about mine at first.  Unfortunately ours did not fall into the same category as DDW's.  One thing is for sure though, there are far more threads on US sensors not working vs paddle wheel sensor malfunctions.

Here was one of the other threads on this: 

  

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But if we are honest, there are few threads on paddlewheel malfunctions because the universal expectation is that they will malfunction, so it is unthreadworthy. The rate is 100% in the ones I have had. Oh you can pull them out (spraying salt water all over the boat), clean the barnacles and other flora and fauna out, polish it up, and have another two days of operation before the next failure. 

The problem with the ultrasonic is the expectations are high - it should just work. And the reality is they don't. 

I guess there is a product I should invent. A paddlewheel thru hull fitting that allows retracting the paddlewheel behind a little door, without having to let in a gallon of water. That would make the usual prescription of "just pull it out every time you dock" actually practical. 

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22 hours ago, DDW said:

But if we are honest, there are few threads on paddlewheel malfunctions because the universal expectation is that they will malfunction, so it is unthreadworthy. The rate is 100% in the ones I have had. Oh you can pull them out (spraying salt water all over the boat), clean the barnacles and other flora and fauna out, polish it up, and have another two days of operation before the next failure. 

The problem with the ultrasonic is the expectations are high - it should just work. And the reality is they don't. 

I guess there is a product I should invent. A paddlewheel thru hull fitting that allows retracting the paddlewheel behind a little door, without having to let in a gallon of water. That would make the usual prescription of "just pull it out every time you dock" actually practical. 

Best case scenario is definitely having a working US sensor like yours which is why I was really excited about it but I ended up with a $500 paper weight.  Agree with your comments regarding the hassle of having to pull the paddle wheel after every sail and in some boats that's more of a project than others.  For me, I just see it as part of the maintenance associated with owning a boat.  If you want accurate information from your instruments and you're using a paddle wheel it needs to be cleaned and pulled every time.  Definitely a hassle but worth it. Even if you don't do that the fix is really easy, pull it out, clean it or if you really neglected it just replace the axle and wheel for a few bucks.  I'll take that over spending seemingly endless hours attempting to diagnose that pos US sensor of mine, all the while constantly mumbling "fucking boats!" to myself (it really is a love-hate relationship at times, no?:D).  ymmv and I get it that others such as yourself have had a much better experience and results.

Which brings me to my next rant!  Not sure I'll ever understand why boats which are arguably one of the oldest forms of transportation still have so many parts that are so unreliable.  You'd think they'd figure some of this out by now.  Hurry up and invent your enclosed retracting paddle wheel and name your price, I'll pay whatever you want for that and be the first in line to buy!

Wasn't there was another type of sensor similar to ultrasonics but a different technology that came out a couple years ago?  Curious to see how they stand up to the test of time. I already have one too many paper weights at the moment, waiting for some real world results on that one first.

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22 hours ago, DDW said:

I guess there is a product I should invent. A paddlewheel thru hull fitting that allows retracting the paddlewheel behind a little door, without having to let in a gallon of water. That would make the usual prescription of "just pull it out every time you dock" actually practical. 

Hmmm ... My old Raymarine paddle wheel (Airmar unit) had just that kind of thru hull: flappy door inside to help keep the water out.  Helped, but not by much.  I guess its tough to come up with a door that both seals tight enough to be effective, but still allow the sensor to get past it.

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I've had the flappy paddle and while it does slow the water that isn't what I mean. I'd have the housing deep enough that the paddlewheel would draw up inside, without ever opening anything into the boat. A door would cover the hole only to keep the wildlife out of the paddlewheel. It would not need to be flush or streamlined or anything, this is only when the boat is docked. Then shove it back down into position, door disappears. No water would change hull sides. 

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  • 2 weeks later...

There are plenty of sonar arrays that will give you very accurate data if you want to spend $100k.  Have to be realistic on the trickle down electronics.  If I already had a ultra sonic one and was trying to get it to work I would do a reverse engineering approach to sort out.  Find a boat who has a well functioning one and get all the data you can from them and try to repeat.  My guess is water airation and transducer placement hull shape are much more sensitive than with a paddle wheel.  Take a basic depth transducer and the know reversing issues you can get via turbulence.

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On 5/9/2021 at 11:58 PM, SASSAFRASS said:

My guess is water airation and transducer placement hull shape are much more sensitive than with a paddle wheel.  Take a basic depth transducer and the know reversing issues you can get via turbulence

This year we moved ours to centerline and back 1m, and the accuracy & correlation w/GPS improved dramatically.  (Though we're still under-reading on a reach at 8kts +, which I'm guessing has to do with transverse flow b/c of heal angle, or maybe a calibration setting in the H5000.)

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IMHO the paddlewheels were never meant to be left in the thru-hull all the time.  They should be extracted and replaced with the plug except when racing.  Around here in the PNW, I have had several paddlewheels broken by hitting sticks and debris in the water.  Leaving them down is a recipe for buying a new one frequently.

We are trying out a Garmin GST-43 next week, and are hoping that it will perform as well as the Signet units.  Will report back.

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Re Physco Tiller & DDW upthread, there was and still maybe an arrangement where the  paddle wheel log transducer did retract into a tubular trunk (pipe) which was closed off by a wt ball valve after the transducer had passed through.  I did see this arrangement many years ago advertised in either a commercial fishing mag or maybe a yachting mag.  It was a pretty simple arrangement, the only drawback was you had to have quite a long trunk inside the hull to fit the through hull, ball valve and stem of the transducer.  Similar system was used in the ships with the chernikeef logs.

Cheers,

Jim

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13 hours ago, Rain Man said:

IMHO the paddlewheels were never meant to be left in the thru-hull all the time.  They should be extracted and replaced with the plug except when racing.  Around here in the PNW, I have had several paddlewheels broken by hitting sticks and debris in the water.  Leaving them down is a recipe for buying a new one frequently.

We are trying out a Garmin GST-43 next week, and are hoping that it will perform as well as the Signet units.  Will report back.

Yeah, IMHO too.  Haven't had any significant failures of either the ancient B&G that was on the boat, or the Airmar DST 810 that came with my Triton 2 displays.  Sure it has to be pulled every day to fight growth.  But that's just the cost of having accurate boatspeed.  Ask me about keeping the bottom clean in the Chesapeake too.  It's not just the transducer that has that problem.  The alternative of course is sailing all the time, or sailing in rough weather.  The thing has done great when it's kept in motion constantly, and for that matter, we've cleaned the bottom pretty well by sailing in 30 knots and craptastic chop.  *Nothing* holds up well to just sitting in the water.  Too many things there that like to grow on other things that are stationary. 

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20 hours ago, JimL said:

Re Physco Tiller & DDW upthread, there was and still maybe an arrangement where the  paddle wheel log transducer did retract into a tubular trunk (pipe) which was closed off by a wt ball valve after the transducer had passed through.  I did see this arrangement many years ago advertised in either a commercial fishing mag or maybe a yachting mag.  It was a pretty simple arrangement, the only drawback was you had to have quite a long trunk inside the hull to fit the through hull, ball valve and stem of the transducer.  Similar system was used in the ships with the chernikeef logs.

Cheers,

Jim

Hmmm - guess it isn't patentable then. No way I am going to pull a paddlewheel every day and clean up the gallon of water that comes with it. The ball valve would be the brute force approach, there may be more of a finesse approach. 

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