Different Tacks - Different Speeds?

[Evadne]

I have noticed this, to a lesser extent, more like up to 10% (1/2 knot at 5kts) and put it down to rig tuning. It is more noticable at higher speeds, not sure it is present at ghosting speeds. We have twin forestays, which inevitably sag to leeward, and the port one sags differently on starboard than on port, when it crosses the starboard one. If you see what I mean.

 

[Robin]

Most wind instruments are capable of adjustment these days at the instrument head, our ST50s certainly are and I do check and tweak ours occasionally for apparent wind angle, otherwise we can get different angles on each tack even in calm water and slack tide. The adjustment on ours is very small usually, ie you move it by HALF the difference, so if for example it reads 40 on one tack and 30 on the other, move the centre (it is a +/- adjuster) by 5 in the required direction. Typically however I might move the adjustment by just +/-2 if at all on the first check after launching. It is actually quite difficult to calibrate with the wind dead on the nose, much better to compare and adjust IMO after trial in calm waters and tacking.

This however is a wind instrument calibration, I suspect that isn't the main culprit here but it could still play a small part.

Robin

 

[BlueSkyNick]

I am glad you made your last point Robin, because I was started to get worried that I was losing the point of this thread.

ie what has the calibration of the wind instrument got to do with the speed of the boat? There seems to be an over reliance on it to point the boat at the optimum angle.

WHat happened to tell tales, windex, sails, and good old gut feel? Just making a point - no need to answer /forums/images/graemlins/wink.gif

 

[Fin]

Once you have gone through the main reasons like rig and impellor then the only main reasons that remains is probably wind shear. Will be different day to day depending on the conditions but it is discussed on the silva website. They are pushing their software that calibrates out the problem...

Silva

Click on the "read more" hyperlink.

Fin

 

[BlueSkyNick]

Excellent, thanks Fin!

 

[Uisteach]

With wind waves (not swell waves) the wave front often sets at an angle to the left of the wind direction. So port tack will usually be slightly faster than starboard tack.