Here's a nice simple article on rig tune from FX Sails.
Basic Rig Tune for Most Sailboats
by Dan Dickison
Where I live—on the southeastern coast of the U.S.—spring is definitely in the air. Sweet-smelling confederate jasmine is in full bloom, the days are warm and the nights are cool, and local boats are slowly becoming more and more active. This is the time of year when anticipation about the impending sailing season swells and owners profess excitement about the new gear they’ve acquired over the winter. Veteran sailboat owners will tell you much of that excitement pertains to new sails. But sails alone (new or old) shouldn’t be any owner’s sole focus right now, particularly after a period of time when you haven’t used the boat much.
Typically, springtime for sailboat owners is a double-edged sword. It’s tinged with all that aforementioned anticipation about days to come on the water, but it also means work—work getting your sail-handling systems ready, making sure the engine is up to snuff and the bottom paint is attended to, that sort of thing. And regardless of whether you sail a Swan 56 or a Catalina 22—or anything in between—if the rig in your vessel isn’t somewhere close to being in tune, all that other work won’t amount to much when it comes time to set your sails.
Rig tune is a simple phrase used to encompass a concept that can be as complex or as straightforward as you want to make it. Essentially, any boat will benefit from having its mast(s) in the right position in the boat with the proper amount of tension applied to the shrouds and stays. Just accomplishing this elementary level of rig tuning will help you prolong the life of your sails, your rig, and your boat. And don’t be afraid to seek guidance beyond the scope of this article. Proper rig tune varies from design to design, so the advice herein is intentionally general.
A number of elements can affect rig tune, including the condition (the shape) of the sails, the nature of the mast, and the age of the boat. To give you a better idea of what that means, consider the words of rigger extraordinaire Brion Toss, who likes to explain that rig tune is all about relationships. ‘When you alter the tension on one member, that affects something else.’ I’m paraphrasing here, but essentially that’s the idea: Loosen the starboard lower on a single-spreader rig and you’ll end up with a mast that bows to port. Loosen the headstay on a masthead rig and you get more forward bend in the middle of the mast, etc. So, to get your rig tuned—or at least in the ballpark—here’s a step-by-step primer:
1. Start by making sure that all your turnbuckles function properly. And while you’re at it, take a moment to lubricate them. (Some riggers specify Lanocote, others suggest Teflon or SeaLube, and some swear by Wichinox, and that’s just a sampling of the products that are available.)
2. Then, back off the turnbuckles so that each shroud or stay is slightly floppy. If a tuning guide exists for your boat, consult that to determine just how much rake (the fore and aft inclination of the top of the mast) your rig should have. If no tuning guide exists, make the headstay turnbuckle hand tight, and keep in mind that this affects the rake of the mast. (Some boats don’t have an adjustable turnbuckle on the headstay. If that’s the case with your boat, no problem, it’s one less adjustment to worry about.)
3. Now, use the main halyard to determine if the masthead is centered in the athwartships direction. To do this, you simply cleat the halyard off and use the end you normally attach to the head of the mainsail to measure how far the masthead is from the chainplates on either side of the boat. At this stage, you intermittently tighten the upper (or cap) shroud turnbuckles by hand and keep measuring until the masthead is equidistant from the port and starboard chainplates and the cap shrouds are snug. Then tighten the turnbuckles on each upper shroud until the shroud is taut. Usually that means turning them an equal number of turns.
4. At this stage, you can check your work by sighting up the aft side of the mast to determine if the mast is straight. If it is straight (the spar doesn’t bow to one side or the other), good work, you’ve got the mast “in column.” If it bows, you simply tighten the lower shrouds correspondingly (or the intermediates if your rig has them) to take out the bow. But don’t over-tighten. Remember, tension on the shrouds (and the intermediates) affects the fore and aft bend of the mast as well, and you’re simply trying to get the spar into a straight position at this stage.
5. Now, sight up the mast from one side or the other to check the fore and aft bend (whether or not the center of the mast is jutting forward). If there’s no perceptible bend, that’s fine. If there’s a slight bend, that’s fine, too. Once you get to this stage, you can begin tightening the lower shrouds by turning them an equal number of turns on each side. As you do this, check to see if the mast remains straight (in column) and adjust accordingly if it doesn’t. If your rig has a single set of lowers, tighten them until they are just tighter than the upper shrouds. If you’ve got two sets of lowers, make them slightly looser than the upper shrouds. If your rig has intermediate shrouds, these, too, should be slightly tighter than the upper shrouds.
6. At this juncture, your rig tune should be somewhere in the ballpark, at least enough so that you can safely have a look at how that setting performs under sail. Of course, this is best done in light to moderate breezes. When you do this, take the opportunity to note how loose the leeward shrouds are when you’re underway close-hauled. And get someone to take the helm for you while you sight up the mast to determine whether or not the middle of the mast sags to leeward or the top of the mast drops off noticeably. These assessments are all clues. Too much looseness in the leeward shrouds and you’ll need to be tighten them; too much mid-mast sag to leeward and the weather-side lower shroud should probably be tightened.
If you really want to get serious about rig tune, there’s a lot of good information available in print and online, and most experienced riggers can guide you through the basics. But keep in mind that even though your shrouds and stays are fashioned from stainless steel, this material does stretch (if only in minute percentages) and it definitely fatigues over time. The most productive step any owner can take regarding rig tune is to keep an eye on it. Be aware if your mast is out of column and consider what might have caused that if that is the case. If there’s a turnbuckle that’s slowly loosening due to vibration, you’ll almost certainly end up with lousy rig tune, and there’s a good chance you might wind up without any rig at all.
About the Author: Dan Dickison is known throughout the sailing community for his in-depth articles on a variety of sailing topics. His resume includes stints as a staff editor at Sailing World, Editorial Director of SailNet, and Editor of Practical Sailor. In those capacities he has written principally about racing, sail handling, and maintenance. He has also written over 50 freelance articles that have appeared in major sailing publications around the world.