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Discussion Starter #1
My boat has an ST70 system with a DST800 speed/depth transducer, wind instruments, X10 autopilot and C90W mfd.

The knot meter has suddenly gone out of calibration, and I can't seem to get it back. I have gone through the calibration procedure multiple times, but strangely, the more calibration points I put in using gps sog, the further out my knot meter reads.

I finally got fed up and did a factory reset on the system and set everything up from scratch and still have the same problem.

When I am setting up data points I can be going 7.5kts and enter that speed as a reference point, continue on at that speed and the instruments will still be more than a knot out.

This is not a case of the impeller being fouled because that has been checked multiple times, and often it reads 1 or more knot fast.

Recently I have also noticed that the wind instruments aren't giving me reliable speeds, and telling me the wind is much stronger than it is, although when motoring on a windless day the wind speed matches GPS speed.

I'm wondering if anyone has some insight into what is going on.

(Please spare me the "Raymarine sucks, buy something else" responses, because that is not an option right now!)


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You are taking into account the boats speed on GPS (SOG) will be different than your knotmeter reading due to current I am sure. How much off is it?

Funny we only used our knotmeter when racing, otherwise the plug is in.

Do your instruments go to the MFD or Are they into a NMEA 2000 backbone?
 

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Discussion Starter #3
You are taking into account the boats speed on GPS (SOG) will be different than your knotmeter reading due to current I am sure. How much off is it?



Funny we only used our knotmeter when racing, otherwise the plug is in.



Do your instruments go to the MFD or Are they into a NMEA 2000 backbone?
Yes, I am making sure the current is minimal when doing the calibration. In the GPS shot I posted there is no current to speak of, and certainly not enough to explain the huge difference between boatspeed and SOG.

The instruments are all on a Seatalk network.

Of course I can ignore the boatspeed and reconfigure the instruments to display gps speed, but that would be giving up! I want to figure out how to make my instruments work properly!

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I’m with you ....I have the same instruments basically as you. 70’s, 95 w MFD, digital radar, wheel pilot, all on NMEA 2000 backbone. I’m glad I did that as I added a Vesper AISB. I would want it to work properly too

My question was I though maybe you MFD was converting the signals wrong. Is the system direct powered to 12 volt or does the MFD power the system?
 

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Discussion Starter #5
Correct me if I am wrong, but my understanding is that all of the devices are on the Seatalk Ng network, and each individual device takes whatever data it needs off the bus. I don't think any one device acts as a "server" to interpret and distribute data to the other devices.

I have 3 ST70 displays, and any calibration changes I make get applied to all 3, and the C90W always displays the exact same data that the 3 ST70s display.

I assume that the MFD just collects data from all the instruments to incorporate it into it's display without any filtering or interpretation.

Am I misunderstanding what is going on?

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Is the STW always lower than SOG? Especially after the factory reset?

Remove the transducer plug from the network, or from whatever converter, etc it is plugged into, and put an ohmmeter across the signal and ground wires. I don't know which wires these are - ground will definitely be had through the shield, but you will need to figure out the signal wire.

All of these work by sending pulses 4 times per rotation. Mark a paddle lobe and slowly turn the wheel one turn while watching the meter. You should see the meter dip open to closed circuit 4 times in one rotation. If it does, then the transducer is probably OK, and the problem is with something downstream (likely a converter box if there is one, because you say all your separate instruments read the same).

Getting less than 4 pulses would explain STW slower than SOG. Getting more I don't have a hypothesis.

Another thing that might cause lower STW is the paddle doesn't turn properly. You said you cleaned it, but did you remove the paddlewheel, clean up the axle and sides and make sure it is turning without any undo friction?

Mark

Edit: I see you said it often reads fast. I don't have a hypothesis for this other than any converter downstream might be bad. If your malfunctioning wind also goes through this converter, it does point to that. There is a common ohmmeter test for wind transducers, but I don't have much familiarity with Raymarine, so don't know what their values should be. I bet a quick google will find it.
 

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Is the DST800 a NK2 or NMEA183. Your plotter may be functioning as a N2K converter and putting the data out on the network. You need to determine if the transducer is faulty or the MFD.... if the DST800 is wired TO the MFD or to a T on the N2K network. I have NO experience with these things... just a thought.
 

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Discussion Starter #8
Thanks for the ideas, I will look into those things further.

Still trying to wrap my head around exactly how all of these things interconnect.

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Our 2011 Bene came with the same ST 70 system. the speed was never right. after replacing the DST 800 once I switched to the CS 4500 ultra sonic sensor/ p79 depth and it has never been wrong since and never needs cleaning. the dst 800 has a direct to ST ng connector and the converter is built in. all the other analog inputs go thru a pod to convert the signal. when I went to the ultra sonic speed which is analog output I had to add an iTC 5 converter to connect the transducer. I removed the pods on the wind and depth and connected to the ITC 5 and now everything works fine. When i converted to the CS 4500 I went back to the ST 70 default settings and the speed is dead on
 

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Discussion Starter #10
Our 2011 Bene came with the same ST 70 system. the speed was never right. after replacing the DST 800 once I switched to the CS 4500 ultra sonic sensor/ p79 depth and it has never been wrong since and never needs cleaning. the dst 800 has a direct to ST ng connector and the converter is built in. all the other analog inputs go thru a pod to convert the signal. when I went to the ultra sonic speed which is analog output I had to add an iTC 5 converter to connect the transducer. I removed the pods on the wind and depth and connected to the ITC 5 and now everything works fine. When i converted to the CS 4500 I went back to the ST 70 default settings and the speed is dead on
Interesting. As far as I can see there is no pod for the wind instruments either, or I have yet to find it. It appears everything feeds directly onto the STng network.

I assume the conversion to ultrasonic speed sensor and separate depth required all new through hulls? That may be where I end up going, but I don't have the budget for that right now.

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St 800 and CS 4500 fit the same thru hull, both Airmar. the p79 depth is a separate shoot thru sensor
 

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Discussion Starter #12
St 800 and CS 4500 fit the same thru hull, both Airmar. the p79 depth is a separate shoot thru sensor
Airmar also makes the UDST800 that is an ultrasonic speed, depth and temp transducer that fits in the same housing as the dst800.. pretty pricey options though.

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Airmar also makes the UDST800 that is an ultrasonic speed, depth and temp transducer that fits in the same housing as the dst800.. pretty pricey options though.

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The UDST800 is the replacement for the CS-4500, which they no longer sell. Yes, it is expensive.

Mark
 

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the UST800 at $ 900 is the replacement for the CS 4500 which was $600 the CS4500 did not have depth in the sensor. the UDST 800 has the depth and is a bit more expensive. If you are going to spend that much might as well go for the DX900 that has speed and leeway in one sensor but it does not have depth, it is the newest technology electromagnetic
 

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Would strongly suggest staying away from the 4500 ultrasonic speedo. Had it spec’d when boat was built. It failed. Got a replacement it failed. Then told RM will no longer support that device nor include it in any new system installation. Had to buy it directly from airmar. Was a ***** to rerun the wire. Got a standard paddle wheel. After 20,000 nm it’s been flawless. Depth is much more important than speed through the water. Would strongly suggest leaving that as a separate sensor. Especially if you’re getting accurate depth now.
Have you looked at your ITC-5? Are all the LEDs green?
 

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Would strongly suggest staying away from the 4500 ultrasonic speedo. Had it spec’d when boat was built. It failed. Got a replacement it failed. Then told RM will no longer support that device nor include it in any new system installation. Had to buy it directly from airmar. Was a ***** to rerun the wire. Got a standard paddle wheel. After 20,000 nm it’s been flawless. Depth is much more important than speed through the water. Would strongly suggest leaving that as a separate sensor. Especially if you’re getting accurate depth now.
Have you looked at your ITC-5? Are all the LEDs green?
My old B&G speedo was forward and to stbd of the keel. I decided to put it on center line for more accurate readings on both tacks. Then the yard broke it and it was no longer supported so I got an Airmar and had the old B&G monitor modified for the Airmar. So I have two housings in the hull for Airmar, one is plugged. Then I got a back up transducer which I don't use but it sits in bilge next to the old stbd side transducer. The housing has a flapper valve which limits water ingress when you pull the transducer to insert the plug. I now put it in when I sail because the paddle wheel was fouling quickly... calibrating it was a PITA.
 

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We’re in the Caribbean. Everything fouls quickly. Pull paddle wheel less than twice a month. Clean with fingers and a wooden fondue stick. Paint with transducer paint. Takes less than 10 minutes start to finish. Good to go. If you go with ultrasonic put it far back. Any detritus or bubbles screw it up. A blast of reverse does as well. Longest I got out of two I had before failure was a couple of months. Not a fan.
I use ultrasound as tank monitors in my phillipi system. They work great but for speed not so much.
 

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We’re in the Caribbean. Everything fouls quickly. Pull paddle wheel less than twice a month. Clean with fingers and a wooden fondue stick. Paint with transducer paint. Takes less than 10 minutes start to finish. Good to go. If you go with ultrasonic put it far back. Any detritus or bubbles screw it up. A blast of reverse does as well. Longest I got out of two I had before failure was a couple of months. Not a fan.
I use ultrasound as tank monitors in my phillipi system. They work great but for speed not so much.
I use an old tooth brush for the paddle wheel... if it's going to be in for long transducer paint.
 

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Discussion Starter #19
Have you looked at your ITC-5? Are all the LEDs green?
As far as I can see I do not have an ITC-5. The DST800 connects directly to the STng bus. The signal is converted internally.

The depth doesn't seem to be a problem, although I don't pay too much attention to it because most of the time the water I am sailing in is well beyond it's sensing range. When I have compared it to charted depths in shallower water it seems to be pretty close.

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if I remember correctly, the only "calibration" of the DST800 when connected via N2K is to set the Depth Offset value. So the speed and temperature values should work fine, unless the paddle wheel isn’t turning properly. If your MFD has a diagnostic screen someplace which can look at all the NMEA 2k data, that would be a place to check and see if the DST800 is sending the correct data.
 
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