The 49'ers have a huge advantage when it comes to rig tune. They use all the same kit so they can do plenty of two boat tuning, and swap equipment to find the fast kit etc. This takes alot of time just sailing along changing one thing at a time, then coming back and doing it again and again, then changing crews to eliminate that variable. Each run could be easily ruined if there is a significant wind speed change or shift. One of the guys at work spent a bit of time in the 49 and says it's the most boring thing on earth two boat tuning, but it works
We are currently working hard on getting Ronin tuned, we had a good start with the tuning guide from Pete Barton. This gave us the basic mast rakes and rig tension. We have recently changed the rig from a prebent rig to a straight rig so are starting from scratch again.
The first thing to get sorted is the rake, this determines the power that the rig developes, generally the more upright the rig is the more power it produces (so upright in light conditions), as you rake the mast back it depowers the rig (stronger winds). Rake impacts on the balance of the boat significantly and produces more weather helm as you rake it back. Getting the right rake is a feel thing, if you are fighting the boat and have tried the usual depowering methods, cunningham and kicker etc. try more rake. Rig tension is the next item. We use a reasonably high rig tension 400lbs plus on the shrouds (30-31 loos gauge). If you don't have enough rig tension two things happen, the forestay sags off to leeward which impacts the boats pointing ability, secondly the windward shroud goes stack which allows the leeward spreader to push the mast to windward which is bad, as it opens the slot and effects the mainsail set effecting both power and pointing ability. Lowers tension is next, tight lowers powers up the lower 1/3 of the mainsail, so ease them a bit if it's windy, this is nearly automatic though if you rake the rig back a hole. We actually tighten our lowers when we rake otherwise it flattens the sails too much. Uppers too little tension and you loose power in light and medium winds as the top of the mast isn't being supported sideways, but if they are too tight the top of the mast isn't allowed to flex enough to act as an automatic gust response. When it's windy we only use enough tension to keep mast in the boat down wind again to gain maximum gust response upwind and to allow the top of the main to blade off.
The key to rig tuning is calibration and therefore repeatability, if you don't know which rig setting was working or not working you can't reproduce it or avoid it, so get the tape measure and rig gauge out and write down where everything is now before changing a thing. Have fun :-)
