Mast Tuning

By Joe Terry
There are two things to consider when tuning the mast: Rake and Rotation


Before adjusting rake, your mast must be vertical from side to side.

How you choose to set your mast rake requires some consideration and compromise. Start with it vertical. If the mast is vertical, the center of effort is forward and the boat is easier to balance fore and aft. The boat has the least amount of hydraulic drag if the boat is balanced and there is no weather or lee helm. However, a sail is most aerodynamically efficient when the leach is vertical, so while the boat may have less hydraulic drag, the sail is not as efficient as it can be.

As you may have guessed, if the mast is slightly raked back, the center of effort is moved back and the more vertical leech results in a more efficient sail; however, the boat is harder to balance fore and aft.

Adjusting your position in the boat will help achieve fore-aft balance. If you're close hauled and experiencing weather helm, move forward and sail the boat as flat as necessary until the helm is neutral or you're as far forward in the cockpit as physically possible. There will be some weather helm when reaching. When running the airflow over the sail is not laminar, so the way to minimize weather helm downwind is to heel the boat to windward. If the conditions are rough you may have to also keep your weight back in the cockpit to minimize digging the bow into a wave.

So what mast rake is right for you?

Mast rake is most critical when sailing close hauled and not as critical when reaching and running. If you're not into racing or are a novice racing sailor, I suggest a vertical setup. This is the most forgiving setup and allows for good overall performance and balance. If you're using a factory stay set this means the forestay is in about the 3rd hole from the top. If you enjoy racing, are experienced and can effectively balance your boat, and maintaining boat balance is always on your mind, you can move the forestay into the top hole. I have seen some sailors even add a shackle to rake it back even further, but in my opinion the negatives outweigh the positives going that extreme. If you're experimenting, try sailing upwind and practice moving forward and aft in the cockpit. The Butterfly also sails best when sailed flat (little heel) upwind, so you can hike accordingly and pay attention to how it affects the feel of the rudder. Your goal is doing whatever it takes to minimize weather or lee helm.

There is no magical formula here. Because the Butterly is suited for a wide range of weight and experience, you need to get out and practice and see what works best for you. Whether you race or day sail, you will get the most performance enjoyment out of your sailing session if the boat is balanced and the helm is neutral. I've talked to a number of customers who have asked for a jib kit to better balance the boat and reduce weather helm. Once they have adjusted the mast properly and pay attention to their position in the boat they are amazed how nice and neutral the Butterfly can be - and how much better it sails!

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Here are two different setups and very different sailing styles: In this photo is Lee McCan sailing 494 and I am sailing II. Lee is one of the best Butterfly sailors I know, weighs less about half of what I do, and is about 25 years older than me. This photo was taken at a single handed national championship and the winds were blowing around 13 knots with gusts in the 20 knot range. Lee has a slightly more vertical setup and is not trimmed quite as hard as I am. Lee has won countless one-design and handicap races with this setup and it works great for him. My setup has slightly more rake and I have a lot more mainsheet tension and you can see the mast bend that results. I'm heavy enough to be able to sheet harder and hike in these conditions to keep the boat flat. I am also as far forward as possible in the cockpit to keep weather helm minimized. For me, this setup works great and I've had good success. This goes to show you need to practice and see what setup works best for YOU.
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Here are some racers at an open Nationals. Boat 9584 is set up with a more vertical setup and 10752 a more raked setup. Mast bend looks similar in both boats so mainsheet tension is about the same. Both boats are sailing fairly flat and with two people in the boat it's easier to keep that balance point forward so the helm remains neutral. If there were only one person in 10752, they would need to basically be sitting between where the two sailors are in the photo.

In order to maintain proper mast rotation the vang with vang arm is necessary. Maintaining proper mast rotation is also more critical with the old style mast, but both rigs benefit when the mast is rotating properly. Many racing sailors prefer the old style rig because it can generate more power upwind with proper mast rotation.

When you set your boat up, you should use a small amount of Vaseline or grease on the mast step to allow the mast to rotate easily. The first setting to insure the mast can properly rotate is proper rig tension. Once your forestay is set to give you the mast rake you desire, adjust the side stays so you can rotate the mast by hand to about 85 degrees in either direction. If your rig is too tight you won't be able to rotate it to 85 degrees and if the rig is too loose you will easily go past 90 degrees.

When sailing close hauled, the vang is primarily used for maintaining mast rotation. Proper rotation of the mast allows the rig to maintain laminar flow over the mast and sail surface. When properly rotated the shape of the mast will blend in nicely to the shape of the leeward side of the sail. If the mast is over rotated it creates some turbulent air at the luff primarily on the windward side of the sail. This reduced the effective sail area and power the sail can generate. If the mast is under rotated the effect is worse as it creates turbulent air over the lee side of the sail, resulting in a stall conditions and dramatically reduces power. Finding the sweet spot can be tricky. The easiest way I have found is to sail with someone who also has a butterfly and make minor adjustments to find the sweet spot. Generally the mast should be rotated about 30-45 degrees when sailing close hauled. It's better to over-rotate the mast vs. under-rotate - especially in light air conditions.

The wind condition and the amount of sheeting affects how much vang you will need to achieve the desired rotation. If the wind is piping and you're sailing fully hiked out with enough mainsheet tension to bend the mast you will need more vang to prevent over rotation. If the wind is lighter, you'll need less vang. While the vang doesn't need constant attention upwind, it is not a "set it and forget it" control - especially if the winds are varying in strength.

When reaching the vang is used to prevent over rotation. It is especially important with old style masts in heavy air. When the old style mast is over rotated on a reach the weak cross section of the mast is taking the load. I have bent an over-rotated mast reaching in heavy air. That was a costly mistake…

When running mast rotation is not important. The vang should be used to control the boom height. If racing you will need to adjust the vang at the windward and leeward marks.

Time to go sailing!