Autohelm ST50 Plus Calibration

[Mort Fligelman]

I hope this is in the right place........I hope so.....because.....the design is lousy and I can't get it to function properly.

My boat came with an Autohelm 4000, ST50 Plus Wind Instrument, and the Tri-Data, Speed, Depth, and Log......

I have played around with them.....thought I finally had them licked, but after all said and done, I can not figure how to set the speed so that it matches my GPS, and check the wind speed against the wind reading on the instrument of the boat on the next dock, and as a result I cannot get the true and apparent wind readings to mean anything.....

The instruction manuals do nothing but confuse me......I can see no logic....

I know that this is vague, and covers a lot of ground but any help would be appreciated.....

I have been able to get the Auto Pilot to function against the apparent wind and the boat will sail relatively well, and the depth offset is functioning quite well.....but the rest is a mystery to me.....so am I only partially retarded?

Thanks

 

[u079721]

This is a confusing topic, but maybe at least I can explain the logic to you. You mention that you have the manual, but you can find a copy online here:

http://www.raymarine.com/SubmittedF...nstrument/ST50/ST50_plus_Tridata_Repeater.pdf

What you need to do is make a run between two points at slack water so that the distance covered over the bottom is the same as the distance covered through the water. What is best is to do it both ways and average the value. When you do this you note the distance that your log reads and compare it with the "true" distance that you get from the chart or from your GPS. You then calculate a correction factor which equals known distance from chart or GPS divided by the distance measured by your knot log. You then follow the instructions on page 31 of the manual to navigate to the Log Calibration Factor screen using the left two buttons, and once there you raise or lower the indicated log calibration factor using the right two buttons to get it to what you just calculated. Once this is done you save your work as shown and you should be good to go for the knot log speed.

HOWEVER, while this is true in theory (and what is in the book), what I found worked best was to use the calculated correction factor to change the already stored Log Calibration Factor in the unit. As an example, I once ran between two range lights with a known distance between them of 5.97 NM, but measured 6.30 NM on my knot log. So I calculated the new "correct" Log Calibration Factor as the old factor (1.56) times the ratio of true to measured distance, or (1.56)*(5.97)/(6.30) = 1.48. I then ran the range lights again and got a measured distance of the true 5.97 NM

IIRC there is no way to calibrate the wind speed.

Good luck!