Rig Preparation and Tuning
The basic goals of rig preparation and tuning is the same on all boats, whether racing or cruising; that the rig is safe and strong enough not to fail, and the rig is set up to ensure maximum performance.
Before stepping the mast: (or check each spring by going aloft in a bos’ns chair)
Check standing rigging for broken strands, check swage fittings for cracks or excess corrosion, check tangs, clevis, and cotter pins, and replace any that are suspect. Make sure the headstay is properly toggled, top and bottom, since the headsails will pull it off centerline. Lubricate sheaves, check halyards, and clean your turnbuckles and lubricate with lanolin or “Never-Seize”.
It is very important to make sure there are no sharp edges that could tear a sail. Tape all cotter pins, pad and tape spreader ends. Small sponges and slippery tape work better than rubber spreader end covers, as they offer less friction. Also look for sharp edges on your foredeck light, and babystay or inner forestay fittings.
When stepping the mast, make sure that the mast butt bears properly on the step. The fore and aft mast butt positioning is critical on race boats with adjustable mast steps and bending masts. For the proper location, consult your sailmaker or boat designer.
Once the mast is stepped, attach the standing rigging and tighten it just enough to keep the rig from moving. (Prior to stepping the mast, compare shroud lengths to make sure they are the same). Step off the boat and check that the spreaders are properly angled. They should be the same height on both sides and should angle up slightly from the mast outboard.
Measure along the rail from the centerline at the stem to equal points on both sides approximately athwartships to the mast and mark these points. If the mast is keel stepped, measure from these points to find the centerline of the partners and wedge the mast there athwartships. Set the turnbuckles to show the same number of threads on each side.
Using a centerline halyard to measure side to side, adjust the upper shrouds to center the masthead. Once centered, tighten firmly. If you have access to a tension gauge, 20% of the rated wire strength is a good starting point.
Sighting up the sail track/groove on the aft side of the mast, align the mast athwartships by adjusting the intermediate and lower shrouds, working from the top down. Once the mast is in column, tighten the lowers and intermediates evenly to about 10% of their rated strength (about 1/2 the upper shroud tension). Final tension will be determined under sail, but be sure to pin your turnbuckles.
Rake is the fore and aft angle of the rig, and proper rake is determined by the sailing characteristics of your boat. Leaning the mast aft increases weather helm, and leaning it forward reduces weather helm. Ideal balance will give neutral or slight weather helm in light air (under 7 knots), without excessive (over 10 degrees) weather helm in heavy air. Keep in mind that weather helm is also a function of heel angle, and all boats will have weather helm when sailed in heavy air.
A bending mast may also be set up with prebend. The amount varies with the cut of your sails, the flexibility of your mast, and the ability to control mastbend. Some rules of thumb: you probably need more than average prebend if you have 1) running backstay/checkstay but no babystay, 2) a full mainsail and/or flat headsails, or 3) a very stiff mast. You probably need less than average prebend if you have 1) a baby stay but no runners/check stays, 2) a flat main and/or full genoas, or 3) a very flexible mast.
Once you have achieved a base tune, you will need to go sailing and readjust for correct tension under load. This should be done under “moderate” conditions with about 15 degrees of heel. The boat should be able to sail without sideways bend or lean to the mast.
Sight up the mast to make sure it is in column on one tack then tack and adjust the leeward shrouds accordingly. Repeat this procedure until the mast stays in line and there is enough tension on the shrouds so that the leeward ones are just taut. Greater tension will add unnecessary compression load and may over stiffen the mast. Less tension means unnecessary sideways lean. Once the final tuning is completed, don’t forget to pin and tape the turnbuckles.
Remember to check for stretch and re-tune as needed during the season. New rigging will stretch substantially.