Each of you who have been aboard for a race, have seen me up at the shrouds before each race with my wrenches and calipers. Â Many of you have written down some numbers…what’s it all about?
Well, I found it hard to believe at first, but have been able to convince myself that it’s true: Â changing the length of the shrouds by just a few millimeters has a profound affect on the power generated by the sails, and especially the balance between the power from the jib and from the mainsail. Â These small adjustments also have a big impact on the ability to point, as they influence the ability to remove sag from the forestay.
It’s easiest to see at the extreme ends: Â sailing with a really soft rig (ie: shrouds about a cm longer than a really taught rig) helps us go much faster in light wind, as the sails can take a much fuller shape, but we can’t point as high (and don’t need to). Â And in really high wind like on Tuesday, without the rig really tight, there is just too much power and the boat is difficult to control.
From the theory, each of the shrouds has a different affect on the sail shape: Â the upper shrouds bend the mast; the intermediate shrouds un-bend the mast; together they enable the backstay adjuster to tension the forestay; the lower shrouds keepÂ the mast fromÂ bending to leeward. Â As a result, it’s not a simple matter of tightening them all a similar amount as the wind increases: Â the ratio among them is also important.
So, I’ve been measuring, tweaking, logging, watching replays of our races, and examining our upwind performance relative to the other boats in the fleet. Â As a result, I’ve been able to develop an approximation of high-wind and low-wind tuning that should be appropriate for PERSPECTIVE. Â There aren’t many other J100s racing out there who have taken the pains to document their settings, but I’ve found one other (which has a shorter forestay, and sets up the mast with less rake than we do, as a result). Â “Miss Marvelous” tuning numbers for high wind and low wind are quite different from PERSPECTIVE’s, but the trend and pattern is similar to what I’ve found.
Comparing what I’ve found with the settings for “Miss Marvelous”, and after some more discussion with Doug Folsetter and Keven Piper, I’ve come up with a draft tuning guide that we can use for a while. Â I’ll keep taking notes and thinking, but let’s use this for now (TWS=”True Wind Speed”, all numbers are distances in mm between the bolts in eachÂ turnbuckle):