ST60 speed running too high

[Tillsbury]

So, on my new boat the boatspeed always read zero. No surprises there. Pulled the transducer for the plug, and cleaned off the junk. Tapped the pin out, cleaned the impeller of weed, put it all back together. It runs reasonably well if not perfectly. I can blow it round reasonably well. Spinning it manually reads out on the display, up to about 10-12 knots when it's going quickly. It has a fair bit of antifouling on the paddlewheel but not a ridiculous amount.

Put it back where it should be, and now I get a boat speed reading. Yay! Except, it's way too high. Apparently I can motor now at about 12 knots. It seems to me it's reading about twice the speed we are actually travelling at. What's the deal here? Is the transducer busted or is there some way I should be calibrating it?

It seems that the previous owner never trusted nor used the boat speed, but I should like to get it working. Anything I should try before shelling out for a new transducer?

[a64pilot]

Needs to be calibrated, easy to do it’s a matter of holding two buttons down, entering the calibration mode etc.
Google ST 60 instruction manual and download it.
Real easy fix and replacement transducers are relatively inexpensive too.
Look around in the boat you should find a plug that looks like the xducer so you can remove it and put in the plug when the boat won’t be moving for awhile

Here is a link
http://c470.jerodisys.com/470Lib/st60sped.pdf

[Bean Counter]

The ST 60 manual shows how to calibrate it. Make sure units used are knots not kilometers. http://c470.jerodisys.com/470Lib/st60sped.pdf

[a64pilot]

See, you got the same answer twice in less than 8 min.
Where else can you get that kind of service

[senormechanico]

Why not just leave it and impress your friends with the boat "speed"?

[Jim Cate]

Make sure units used are knots not kilometers.

for sure! The error being ~a factor of two is pretty suggestive of km/hr, and also that is a really big error to be attributed to tweaking!

Jim

[SaltyMetals]

Tillsbury, you don't have to struggle to see if you are getting kph or knots. i have an ST 60 system as well. on your speed dial there shld be three letters "KTS" for knots. i dont know what it shows for kph but clearly what you need to be seeing is "KTS". nothing else.

If this is what you are getting there is a simple calibration procedure which the others have also referred to. it is all in the Raymarine book (or online).
andrew
"Genial Bee"

[moseriw]

this is in fact a bloody f... stupid unit to adjust. one way may be to mileage it out but homing in is difficult too. Why o why isn't there a way to set the numbers directly. Ill and stupid design but the unit itself is very good quality.

[SaltyMetals]

Patience Mozzie ! It is relatively straightforward, not rocket science. From what i remember there is a choice in the calibration procedure to apply a % (+/-) adjustment or to accept what the SOG is showing from GPS measurements. The latter of course can be affected by currents so is not necessarily the best choice to take depending where you are and time of day. Easier to do it at exactly HW or LW when there is no current then you just accept the SOG measurement. You could of course choose a +20% setting and then impress your friends on board. They would be none the wiser.

Having said that i find i can get the speed readout correct at say 6 kn but at 8-9 kn it is wrong, similarly at 2-3 kn it is wrong when comparing against the SOG from the GPS signal.. Am not talking about 50-100% wrong but maybe 5-15% wrong. At the higher speeds it could be foaming under the hull that causes the error. But who cares? A good wind and a good sail and it puts a smile on yr face.
Andrew
"Genial Bee"

[roverhi]

Originally Posted by moseriw

this is in fact a bloody f... stupid unit to adjust. one way may be to mileage it out but homing in is difficult too. Why o why isn't there a way to set the numbers directly. Ill and stupid design but the unit itself is very good quality.

It's been awhile since I've done it but it wasn't any big involved process. At slack tide, fired up the GPS, set the throttle under power and matched St60+ to the GPS speed according to the Raymarine instructions. The log function was within a percent or two of the taff rail log readings on multi thousand mile sail. Now setting up the Wheel Pilot was another story doing is solo.

[a64pilot]

The old ST was easy to adjust, the new I series is a PIA from what I can tell, it seems you can only make it agree with GPS speed, you can’t slowly adjust up or down like the old ST

[44'cruisingcat]

Could be showing KMH instead of KTS.

Mine occasionally changes units of it's own accord. Other people I've spoken with have had it happen too.

More disturbing when the depth changes units on you and you suddenly realize it's not 3 metres deep but 3 feet.

[Tillsbury]

Thank you very much, everyone. I will read the manual (should have done that to start with) and find a nice zero current day to give it a whizz. The electrics on this boat are so dicky that I wasn't trusting anything at the time. Need to go over everything that's been added and probably rip it out and reinstall. The original Bavaria electrics are of excellent quality -- everything subsequently added has been done by a blind monkey.

[sailjumanji]

Originally Posted by 44'cruisingcat

Could be showing KMH instead of KTS.

Mine occasionally changes units of it's own accord. Other people I've spoken with have had it happen too.

More disturbing when the depth changes units on you and you suddenly realize it's not 3 metres deep but 3 feet.

Something similar. When wife and I took our trip from Texas to Bahamas for a few months in 2016, for weather forecast we used an Inreach subscribed to OCENS weather service. Wind direction and speed, wave and swell direction and height, etc. - in four hour increments. We found them extremely accurate on predicting wind direction and speed - even the shifts. Swell and wave direction spot on. However, they were consistently underforecasting wave height. We had some 2-3 ft forecasts for open water crossing that we were getting hammered on (with much larger waves). I called them to confirm we were getting forecasts in feet, and they assured me we were. About a week later their head meteorologist called and apologized - after having looked as some of their forecasts and our observations - and said they had been sending us meters instead of feet! Huge difference in wave height of 2-3 ft vs 2-3 meters. It was all much better after that. Apparently few people use Inreach for OCENS, and there was an interface issue.

Re: the ST60, it takes about ten minutes to correct the instrument, including the time to read the instructions. Most difficult thing is finding an area without current so you will know that SOG (GPS) equals speed thru water. Setting an i50 is even easier.

[Alita49DS]

As others have said, the instructions are clear enough. What they do not say is what a pain the whole thing can be. The design of the ST60 is a model of obfuscation. The Airmar transducer is a nightmare to replace. One is not allowed to cut the wire from it. The location of the transducer is generally forward of the keel and the instrument at the stern. Threading through the whole boat. Just great. The unit itself seems antiquated in an era of electronics. As for a water temperature reading, mine is out by miles.

You wrote "Tapped the pin out, cleaned the impeller of weed,"

Personally, I would not tap the pin out as it is only a friction fit. Next time you will loose it. In the old days the pin was threaded to the body. That was when the transducer was made in the UK and before some bean counter had worked out how to cheapen the whole thing except for the end user.

An easy way to remove crud is to take out the transducer and insert the blanking plug. Then get a shot glass, fill it will vinegar and leave the paddle wheel body in that over night. Then clean gently with an old tooth brush. Everything comes off easily without the risk of loosing the pin friction or putting the paddle wheel back the wrong way round.