Sonar

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There are 2 Sonars in our club. Ater stepping the masts this season we both set the rig tension to 220 pounds, the other boat pointed a lot higher. I checked the tension on mine and it was 185 pounds, his was 120. Does lower tension give better pointing?

Thanks for your question on Sonar tuning. Obviously, as you have discovered, even small adjustments can make a big difference in a one design boats performance. There are so many variables that go into matching pointing and speed it is tough to pin it on just shroud tension. However, here is a list of things I would check on the tuning and setup between the two boats.

-Check the mast butt position. This can be tricky if the boats are not the same manufacturer (Eg. Ontario vs. Ryder) but the butt should be set according to the tuning guide.
-Are the mast rakes set the same. Check your headstay length.
Easiest way (when the mast is up) is to detach the headstay from the bow and lay it against the face of the mast. There should be a black band on the mast. Mark the headstay with a "sharpie" at the top of the band and reattach. Then measure from that mark to the center of the pin.
-Check your mast blocking. More mast blocks behind the mast in light air will induce more pre-bend making a flatter main and creating headstay sag.

A few basic concepts for Sonar tuning.
-Rake must be set near 26' to point with the "pros". 25'11" is about as short as you want it to be.
-In light air you need pre-bend to flatten the main, sag the jib and help you point. More sag in the headstay=more power and a better angle of attack so you can point higher. You may need to work on finding the setting that is best for your sailing style but, in light air, try more blocks behind the mast and get some sag in your headstay.

You briefly mention lower shrouds in your note. The lowers should be set very, very loose. A tension gauge is not used in setting the lowers. I set my lowers by sailing upwind and loosening or tightening them so that the middle of the mast "sags" about 1/2" in most conditions. The lowers will be so loose that they will make 10-12" "circles" when standing at the dock.

Finally, shroud tension will have an impact on performance as tighter uppers can pull the headstay tight. That said, the difference you state (about 60#) would not make an enormous (read: 3-5 degree) difference in pointing. It is more likely that something else is askew in the setup.

Answer by Brian Hayes