Raymarine ST60 wind indicator over-reading

[ste7ve]

I have an issue with my wind indicator and a query regarding the speed they rotate at and their calibration.

At the end of last season I found my indicator was over-reading rather considerably by anything up to 30% (on a club rally after a long beat in a strongish wind I told my fellow skippers I had seen over 40 knots at one stage. I was then laughed at with others saying they hadn't even seen 30 knots).

On the display head you can set a factor in theory to calibrate the unit. However without a reference that is very difficult. Raymarine on their support pages don't seem to have any advice, other 'adjust accordingly'.

Sitting in my boat looking at half a dozen other ST60 indicators going round I was amazed to see the huge difference in speeds. Presumably that is likely to be down to the bearings?

My indicator is a replacement one and only a year old and seems to rotate very well and the factor is set at zero.
One has to assume that an indicator in perfect, as new, condition just needs the zero setting.

When first installed the indicator seemed to read OK.

So any views on what could make my unit start to over read so much?

Thanks

Steve

 

[NPMR]

Can you borrow a handheld meter from somewhere and get a guide as to what the differences are (remembering that at the top of the mast, the airflow is likely to be faster)?

 

[johnalison]

I think it would be a mistake to calibrate it on the basis of a peak reading. It is not uncommon to record an exceptionally high figure in gusty conditions. I assume that some vortex or other produces a localised blow much higher than elsewhere. The highest figure I have recorded was 57kn. This was when sailing in sheltered water near a Swedish Island (Store Dunen). While it was fairly windy, I would have expected a peak figure around 30kn. I have had occasional high figures since then, and I know of others who have met the same.

I would suggest that you compare your reading with that of a nearby boat during steady conditions of around 15kn. You might even be able to pick up a neighbour's data by wifi and display it near your own for comparison. A hand held meter at deck level will be showing something like 30% of that at the masthead.

 

[FulmarJeddo]

I'm sure there has been a thread on this in the past. The earlier transducers spin at a different speed to the later ones. I have had a search for "ST60 wind calibration" and loads come up. I haven't found the post that explained the calibration to sort mine out. I had a ST50 transducer and display. The display went faulty and I changed it for a ST60. The early ST60 used the same transducer as the ST50 with the round cups. The later had the egg cup shaped cups. The default ST60 calibration is 0.7, but I can't remember if that is for the old or new transducer. I'm sure if you search the old posts you will find the calibration factor you need. It was at least 3 or 4 years ago I changed my display.

 

[earlybird]

Here

 

[ste7ve]

Thank you very much for the table which I have not seen before.

I am on my third MHU and the original was the old ST50 type from 2012, which I replaced with the modern ST60 unit.
However I did not know about the calibration factor change.

The replacement started to only show the wind speed intermittently after a couple of years.
Eventually I discovered a note on Raymarine documentation saying that to install a ST60 MHU on a ST50 mount you have to remove an O ring in the mount, which sounds counterintuitive.

When the mast came down for rigging work last year, I could inspect it all and the O ring was in there and water had clearly got into the connector because some of the MHU pins were corroded.

Hence why I am now on my third MHU.

I will check out the calibration next time I'm at the boat.

Thanks

Steve