Calibrating ST40 wind instruments

magnusmurphy · #1 (**permalink**) 06-19-2008

Hi

My family and I have "done" the Thorney Path from the East Coast down to Grenada over the last seven months. We're currently getting ready to haul the boat in Grenada. We had a fantastic adventure!

Over the months of going to weather I've been irritated by a malaligned ST40 wind indicator. I've tried to reallign and recalibrate it and followed the book as well as I could. After you do your few 360 turns (or not - I tried with and without with no observable difference), you get to "allign" the needle by pusing the up or down button. Problem is at this point it is whipping widely around and there seems to be no sense or reason for where it is pointing. Getting it to point into the wind becomes a matter of luck. Other cruisers have told me thay have the same problem and simply ignore the thing.

Then I've noticed that the indicator is accurate on port tack but way off on starboard. Currently it shows the wind accurately on close hauled port tack, but when on the corresponding starboard tack it shows the wind on the starboard quarter.

What can I do to fix this annoying problem?

Thanks

Magnus Murphy
sv Losloper
Shearwater 39

negrini · #2 (**permalink**) 06-19-2008

For adjustment, you should go motoring right against the wind, on a windless and flat sea day. This way, you'll increase your chances of a straight heading (0 deg.). minimizing oscilations. Then follow adjustments like book says. Your system should be linear all the way 360 deg around, otherwise your top mast sensor might have a problem. It is not possible to align a specific sector, as it is expected to have full linearity around.

trantor12020 · #3 (**permalink**) 06-20-2008

You could send someone up the mast and give him/her instructions to spin the pointer or hold straight ahead whilst you adjust the ST40 reading. Its also possible that your mast top transducer is faulty. I had similar problem with my ST60 transducer. It was faulty.

Quickstep192 · #4 (**permalink**) 06-20-2008

The tail on my mast top vane is slightly warped causing it to give different readings on port and starboard tacks. I think both are inaccurate but port "feels" right because it has a closer tacking angle. Either that or the angle of heel affects the impact of the warped tail more on one tack than the other. One way I though to get dead on the wind was to anchor, let the boat settle in and then calibrate the instrument.

Good luck. It's frustrating at best.

JimsCAL · #5 (**permalink**) 06-20-2008

Could also be a problem in the cable running from the top of the mast to the readout. I had/have a very similar problem with my Standard/WM wind direction display. They told me to remove the transducer from the top of the mast and plug it in directly to the display (they have same connectors). Everything works great when plugged in directly so the problem is in the cable. So that's on the list to be changed next time the mast comes out.

sailingdog · #6 (**permalink**) 06-20-2008

This is why I upgraded to TackTick instruments last year.

No more wiring issues.

Quote:

Originally Posted by JimsCAL

Could also be a problem in the cable running from the top of the mast to the readout. I had/have a very similar problem with my Standard/WM wind direction display. They told me to remove the transducer from the top of the mast and plug it in directly to the display (they have same connectors). Everything works great when plugged in directly so the problem is in the cable. So that's on the list to be changed next time the mast comes out.

cnc33voodoo · #7 (**permalink**) 06-20-2008

i have the same st40.it has a rotavecta for the mast top unit.
completely different from a st60 which has an actual wind direction not an offset cup such as the st40.the way i calibrate my unit is i just manually set it according to the wind direction i get from my windex unit.once on the water i had to make a couple adjustments to get it acurate but now it works perfect.that going around in circles crap never worked properly.
works perfect now but the optional screen that tells you what direction to steer is useless.

magnusmurphy · #8 (**permalink**) 06-21-2008

Thanks for the advice. We were beating into 30 G33 knt winds and huge seas today (3 hours to do 3miles CMG) to get to Grenada Marine where we're hauling on Monday. It was again quite frustrating not to be able to trust the intrument wind direction. I guess that's why I fly a big Canadian flag at the back - it shows me the apparent wind direction pretty well!

Magnus

joesail3 · #9 (**permalink**) 10-20-2008

Well, gang, I'm on my 4th Rotavecta unit. Everytime they send me one the symtoms of why it doesn't work seem to change. So far I'm not impressed. I've owned it for 8 but it only worked for 3 months. Good thing I have an electric halyard windless on my Nonsuch 30.

brak · #10 (**permalink**) 10-20-2008

Quote:

Originally Posted by sailingdog

This is why I upgraded to TackTick instruments last year.

No more wiring issues.

Is the wind transmitter also wireless? How do they power it?
I read the user guide on the website and it certainly makes no mention of wires for the wind instrument, but also says nothing about it's power source.

P.S. Never mind - found it, all solar powered.Well, just need $2500 to spare.