Continuation of Racing to Win by Steve Milby
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Tuning the Rig of a C-25

Mast Tuning

Before we discuss the processes that should be used in tuning your rig, let’s think about how each stay functions. Each stay has a specific purpose, to provide support from a specific direction, and to prevent the mast from bending in an improper direction or to an excessive extent. If your rig is properly tuned, the tightened backstay will pull the top of the mast aft. The headstay will limit the distance that the top of the mast can tilt or bend aft. The forward lowers will resist the pull of the backstay and prevent the lower part of the mast from moving aft. At the same time, the forward lowers will provide lateral support to the lower portion of the mast, to keep the lower part of the mast from sagging to leeward. The uppers will provide lateral support to the top of the mast, to keep it from sagging off to leeward. As the tension on the backstay adjuster increases, it will exert a downward force on the mast. The mast step and keel will resist the downward force on the mast. Since the mast can't move downward, to release the pressure, the mast will bow in the middle. Because the forward lowers are adjusted snugly, and the aft lowers are adjusted loosely, the lower part of the mast can only bend one way, i.e. forward. As the lower part of the mast bows forward, the aft lowers will become taut, and prevent the mast from bending so far out of column as to damage the mast. In order for the backstay adjuster to work properly, the stays have to be adjusted with differing tensions, so that they allow the mast to bend in the proper direction. If all the upper and lower mast stays are snugged down to more or less the same tension in all directions, when you pull on the backstay adjuster, the mast won’t bend, because the stays will prevent any part of the mast from moving in any direction.

Boat Without Adjustable Backstay

Begin tuning your rig by alternately tightening the headstay and backstay turnbuckles until the headstay and backstay have little or no sag, but so that they are not bar-tight.

Next, loosen all your lower stays just enough to take the tension off them. Then, tighten the upper stays snugly by an equal number of turns on each side. Next, take your jib halyard, and use it as a measuring device (you might need to tie a piece of line onto it, to lengthen it), to make sure that the distance from the top of your mast to the chainplate for the upper stay on the starboard side of your boat is the same as the distance from the top of your mast to the chainplate for the upper stay on the port side of your boat. If the distance is not equal, adjust your upper stays until the distance is equal on both sides. That will ensure that your mast does not lean more to one side than the other.

Now, adjust your forward lower stays until the slack is just taken out of them. Then continue tightening them, alternately by an equal number of turns, until they are as tight as you can comfortably get them by hand. Then do the same with your aft lowers. Lie down on the coach roof, and sight up the mainsail track, to see if the mast is straight. If so, then use tools to tighten each lower stay a little more, alternately by an equal number of turns, until the tension of the lower stays is snug, and equal all around. Sight up the mast again to be sure it is still straight. If it is not, then make such adjustments to the lower stays as are necessary to make it so.

Tighten the locknuts on all your turnbuckles, including the uppers, lowers, headstay and backstay. With these adjustments, your mast will not be perfectly adjusted, but it should be "in the neighborhood." Sail the boat, and observe whether it has excessive weather helm or lee helm. It will probably have excessive weather helm. If the boat has excessive weather helm, readjust all the stays so that the entire mast is tilted further forward. If the boat has excessive lee helm, readjust all the stays so that the entire mast is tilted further aft. If you do not have an adjustable backstay, you are done.

Boat with Adjustable Backstay

If you have an adjustable backstay, you have a little more adjustment to do. Make sure that the tension on the backstay adjuster is completely released. Then loosen the turnbuckle on the headstay until the headstay is slack. Next, adjust the aft lowers until they are slack. Then apply strong tension to the backstay adjuster. Adjust the headstay so that the mast tip bends aft about 8-9 inches when the backstay adjuster is tensioned. When the backstay adjuster is eased, the headstay should be quite slack. Adjust the aft lowers so that they become tight when the backstay is tensioned. The way to do that is to apply the maximum tension on the backstay adjuster. Then adjust the aft lowers until they just become taut. When you release the tension on the backstay adjuster, the aft lowers will become slack. When you re-apply the backstay tension, the aft lowers will become taut again. To increase the amount of mast bend, loosen the headstay and the aft lowers, but do not allow your eagerness for speed to cloud your judgment. 

Sail the boat again, and observe whether it has excessive weather helm when the backstay adjuster is fully tensioned. If the boat has excessive weather helm, then readjust all the stays so that the entire mast is tilted further forward.

Using a Loos Gauge to Tune the Mast

I don’t own a Loos gauge, and have never used one to tune my rig. I make sure that the mast is vertical, adjust the stays so that they are generally snug, and adjust the rig to allow the mast to bend within safe parameters, and no more. Then I test-sail the boat after tuning the rig, to see if it is performing to my expectations. 

Having said that, I believe that most sailors would benefit from using a Loos gauge. Once you have tuned your rig so that the boat is very fast, a Loos gauge can help you accurately reproduce that same setting, after working on your mast or shrouds, or after lowering and raising the mast. 

Derek Crawford is one of the most knowledgeable C-25 racers that I know, and he uses the Loos gauge to tune his rig. With his permission, I am reproducing his recommendations for tuning with a Loos gauge.

Excessive Weather Helm

If you have to pull hard on the tiller to keep your boat from heading up to windward, then you have too much weather helm. (This assumes that you are flying approximately the correct size sails for the amount of wind, and that your sails are properly trimmed.) Whenever you have to pull on the tiller in order to hold the boat on course, the rudder is creating resistance. Excessive weather helm causes drag, which slows the boat significantly, and makes you arm-weary. Whether you have the balanced rudder or the standard rudder, you can eliminate excessive weather helm by adjusting all the shrouds and stays so that the mast leans slightly more forward. 

Start adjusting the rig by letting out the backstay turnbuckle about 3 turns, and then tighten the headstay turnbuckle 3 turns. Then readjust the lowers on both sides accordingly. Sail the boat and see if the tiller pressure is still too strong. If so, adjust the headstay and backstay about 3 more turns, and again adjust the lowers accordingly. Continue adjusting the rig forward until the tiller pressure is light, but do not completely eliminate weather helm. A slight amount of weather helm is necessary for safety, but you can minimize it.

Excessive weather helm can be caused by improper sail trim. When a C-25 is beating to windward in moderate to strong winds with a 150% genoa, the sail should be trimmed in until it is about 8-9” from the spreader. In the gusts, dacron sailcloth will stretch, and the distance from the spreader will increase. When that happens, you should pull the jibsheet in until the distance is about 8-9”. When the wind gust eases, and the jib is closer than 8-9” to the spreader, you should ease the jibsheet back out. 

When you have excessive weather helm, try easing the mainsheet traveler to leeward, until the mainsail begins to luff slightly. If you ease the traveler all the way and the boat is still experiencing excessive weather helm, it is time to think about reducing the size of your headsail, and perhaps tucking a reef in your mainsail.

Excessive weather helm can also be caused by carrying too much sail in too much wind. Even a boat with a well-tuned rig will have excessive weather helm if it is overpowered. The only remedy is to reduce sail area.

Recently we were racing, and I was flying my 150% genoa, and had a flattening reef in the mainsail in the maximum amount of wind for a 150. Nevertheless, I could take my hand off the tiller for 5-6 seconds without the boat rounding up, and could hold it on course easily with the thumb and forefinger, except in the strongest gusts, when we were clearly overpowered. A heavy weather helm is not inherent in a Catalina 25, even with the original design of rudder. With good mast tuning and correct sail choice, you can enjoy a light, comfortable helm.

Deciding When and How to Reduce Sail Area

When the boat is heeling excessively, you are confronted with the dilemma of whether you should reduce the size of the headsail, or reef the mainsail. As a general principle, the headsail generates the most forward drive, and the mainsail helps the boat point to windward, so you need to achieve the correct balance between them in order to sail efficiently to windward. The particular disadvantage of the mainsail, however, is that it is more responsible for excessive heeling and for excessive tiller pressure than is the headsail. When a boat heels excessively, and when it has excessive tiller pressure, it is generating drag, which drastically slows the boat. 

On a C-25, which has a masthead rig, the jib is the principle driving sail. It generates the most forward drive and the least heeling moment. Therefore, when racing, I want to fly the maximum amount of jib that the boat can carry. 

The mainsail generates much less forward drive and much more heeling moment, so, when you are overpowered, you want to use proportionately less mainsail area. However, the leech of the mainsail helps drive the boat to windward, so you always want to keep some amount of mainsail area flying and properly shaped.

When my boat is overpowered, and I am trying to decide whether to reef the mainsail or to reduce the size of the headsail, I completely ease the mainsheet while the wind is gusting. If the boat does not continue to heel excessively when sailing under jib alone, then I conclude that the size of the jib is not excessive. If the boat is nearly overpowered when I ease the mainsheet, then I reef the mainsail. If the boat has a little more latitude before it becomes overpowered, then I don’t reef the mainsail, but I depower it by flattening it, moving it’s draft forward and increasing backstay tension. Let me explain the logic that I use to reach these conclusions. 

Because it is limited by its design, a sailboat can only stand up to a certain maximum amount of drive from the combined area of the mainsail and jib. If the boat is heeling excessively when sailing on the jib alone, then the boat won’t be able to stand up to the addition of more sail area and more power from the mainsail. In that case, if you reduce the size and power of the jib, it will enable you to add the power of the mainsail without overpowering the boat. Whenever I reduce the size of the headsail, I also usually tuck in at least a flattening reef in the mainsail. (My mainsail has a racing shelf foot with a flattening reef.) If that does not sufficiently relieve the tiller pressure or excessive heeling, then I tuck in the first full reef. 

If the boat is not heeling excessively when sailing on the jib alone, then that tells you that you can restore some of the power of the mainsail without overpowering the boat, but, if the boat heels excessively when you do so, you should at least flatten the mainsail, and perhaps tuck in a reef. When you reduce your mainsail area, it will help the boat point to windward, it will reduce the tiller pressure, and the mainsail will not generate so much heeling moment. 

Excessive heeling and excessive tiller pressure are the two observable conditions that impede the boat’s speed and windward ability. Your objective is to find the combination of mainsail and headsail that minimize those adverse conditions, while maximizing the boat’s speed and windward ability. When you observe that those adverse conditions are abating (i.e., you see that the boat is not heeling as much, and you feel less pressure on the tiller), then you will know that you have improved the balance of your sailplan.

Conclusion

After reading this article, you might think I spend a lot of time on the racecourse impeding the progress of other boats, blocking their wind and using the racing rules as an offensive weapon. I absolutely do not. While you must know how to do those things to race against the toughest opponents, you will generally benefit the most from meticulous boat preparation, and from learning how to make your boat perform its best.

In any sport, you are rewarded for your technical knowledge of the sport, and for your hard work. Yacht racing is a wonderfully complex, mostly cerebral sport. It requires that you understand not only its complex right-of-way rules, but also such diverse esoteric subjects as aerodynamics, hydrodynamics, architecture, engineering, meteorology, psychology, and marlinspike seamanship. Most of us prefer sailing to powerboating because we are intrigued by the complexity of sailing, and because powerboating does not satisfy our desire to be challenged. Yacht racing forces you to learn more about all these subjects, and will make you a smarter, safer sailor. The knowledge and skill that you acquire from racing will not only serve you well when you are daysailing on your inland lake, but also when you are making long, open-sea passages, chasing your dreams.