How to Tune Your Rig
Whether you would like to get the optimal performance out of your sailboat or just trying to keep your mast upright, a well tuned rig is the key. The goal of a properly tuned rig is to have a mast that is straight, better control of sail shape, and proper helm balance in a variety of weather conditions. The ideal mast should have a slight rake (lean) aft and be perfectly straight side to side.
Let’s begin with mast rake which is determined by headstay length. Rake affects the helm by moving the center of effort of the sails. A longer headstay gives more rake resulting in more weather helm. My Catalina 30 is designed to have a rake of 5-10 degrees. To calculate rake, hang a plumb bob from the main halyard and measure from the aft side of the mast. For a 10 degree rake adjust the headstay and backstay so that the plumb bob will drift about 1 inch aft of the mast.
The next step in rig tuning is to tighten the shrouds to center the mast laterally in the boat. With the shrouds relatively loose, pull a steel tape measure up on the main halyard. Pull the tape hand tight and measure to the upper shrouds chainplates on each side. Adjust the upper shrouds until you get the same measurement port and starboard. Using a wrench to keep the shroud from spinning and small screwdriver to turn the turnbuckle, take equal turns on each side until the turnbuckles are hard to turn. Check the center of the masthead again with the tape on each side. The lower shrouds should now be hand tightened enough to keep the mast straight. The aft lowers should be looser than the forward lowers, which are looser than the upper shrouds.
We are now ready for a sea trial. In about 15 knots of wind and sailing close hauled tighten the upper shrouds on the leeward side to remove slack. Keep track of the number of turns on each side while tacking back and forth. Tighten until the uppers are snug on the leeward side with the boat well heeled.
Now that we have the correct tension on the upper shrouds, we are ready to straighten the mast with the lower shrouds. Tension the lowers until the mast appears straight when sighting up the sail track. In a fresh breeze under sail, the leeward side lowers should be slack and the uppers snug. Secure turnbuckles with locking wire and cover with rigging tape to prevent chafe.
Again the upper shrouds should be the tightest. The forward lowers tight and the aft lowers less tight. The mast should be perfectly straight while sighting up the sail track with a slight rake aft.
The basic adjustments for tuning a sailboat rig are actually quite easy and not the mystery that some people fear. Give it a try. Your rig and helmsperson will thank you.