Wally Cross on Tuning Your Rig
by David Dellenbaugh

If you want to go fast upwind, one of the first things you need to do is make sure that your rig is tuned properly for the wind and wave conditions. Wally cross, a long-time sail designer and mainsail trimmer, shares his approach on how to set your mast for closehauled speed.

DAVID: Wally, what are your priorities for rig tuning when you race on a boat for the first time?

WALLY: If the boat is a one-design I always try to do some homework prior to the first sail. I research which sailmaker is having success in the class and read over their tuning guide for clues about the boat. I view tuning guides as a good starting point but not necessarily the final word. Most of them are a bit dated, but they do eliminate the need for a lot of experimentation.

Wally Cross has been a sailmaker since 1973 and enjoys sailing in owner-driver classes. His race credits include three wins in the Canada’s Cup and many successes in one-design, inshore and offshore events. Wally’s passion is helping boats sail faster through rig and sail settings.

My first tuning goal is making sure there is symmetry in the rig, tracks, spreaders and so on. IT is really important that the main and jib (genoa) set up the same on each tack. Once I am convinced both tacks are similar, I mark jib tracks, halyards, backstay, jib sheets and inhaul for future reference.

For every boat, it’s important to develop a tuning sheet that gives the trimmers adjustments for light, medium and strong winds. This guide should have setting numbers for the jib halyards, jib sheet, lead position, main traveler, backstay, and vang in all three wind ranges. Having a resource like this takes some of the mystery out of setting the rig and sails. However, the tuning process constantly changes, so you need to update it continually with real race data.

Is it important to get your mast straight in the boat? If so, how do you achieve this goal?

When I view a mast for the first time I check to make sure it is set up straight side to side. To achieve this, start by positioning the tip of the mast on the centerline. There are several ways to do this.

I think the easiest method is to get a low-stretch tape measure with a mainsail slug that fits your mast. Attach the end of this tape measure (right at the slug) to the main halyard and hoist it to the top of your mast. Then measure the distance to identical points on each side of the boat (such as the jib tracks or the sheer line) that are equidistant from the centerline. Adjust your upper shrouds so this measured distance is the same on each side.

Once the tip is centered, you have to get the entire mast on the boat’s centerline. Start tuning the diagonal shrouds until the middle of the mast is straight side to side. It’s best to do all this in morning or evening when there is no wind.

How do you figure out the right amount of rake for a boat? Do you change rake for the conditions?

The purpose of raking the mast is to help your boat get the best VMG upwind. To sail at the proper target speed and angle, you need the right amount of rake. If you rake the mast too far aft, the boat will have too much helm and drag; too far forward and the boat will want to drift to leeward when you are sailing close hauled.

There are many ways to measure rake, so you should find one you like and use it consistently. On a one-design boat I will first measure rake using the method described in the best tuning guide for the boat. In many classes the normal technique is to measure from the bow to a reference mark on the headstay. To locate this mark, take a jib halyard to the mast and mark it exactly at the black band. Then, with the halyard cleated, swing it out to the headstay and put a mark in the same sot. Other classes, like the Melges 24, measure rake from the top of the mast to the intersection of the hull and transom.

For boats that don’t have a tuning guide, I attach a full bucket of water to the main halyard and let this hang vertically with the boat level for and aft. Then I measure from the aft side of the mast to the point where the main halyard intersects the boom.

For a ballpark rake setting, this distance should be about 2% of the boat’s I measurement. For example, a Catalina 30 TR has an I of 43, so its main halyard should hang roughly a foot (43 x .02 = .86 feet) aft of the mast at the boom.

Another way to determine how much rake you need is by sailing the boat and seeing how much windward helm you have. In the perfect world with winds from 10 to 15 knots, your boat should have between 5 and 8 degrees of helm. If you have less helm that this, add rake; if you have more helm, angle the mast forward.

On many boats, you should change your rake based on wind speed. Again, I like to have three rake setting sot go with light, medium and strong breeze. In light winds I use more rake on most boats because it helps bend the mast more, which flattens the main forward and lets me use a softer headstay. This helps make the jib more powerful, and the flatter entry on the main allows the slot to work. More rake in lighter air also gives the boat a little more helm, or feel.

In medium breeze, set the rake to get 5 to 8 degrees of helm. This is just enough helm to assist the boat when sailing upwind, but not too much to hurt your speed with excessive drag. In big breeze, I reduce the rake, if necessary, so the boat doesn’t have too much helm. I also tighten the headstay a lot. A straight headstay in breeze reduces helm, minimizes extra drag on the jib and allows the boat to go faster.

How tight should your shrouds be and how do you measure this? How often do you adjust rig tension?

Rig tension seems to be one of the biggest tuning mysteries, so I try to keep it simple by using my eye and basing adjustments on the boat’s performance. Before every start I measure turnbuckle length on all the shrouds - this way I always know the numbers we are suing in each race sailed.

I view rig tension like a flap on an airplane. In lighter winds the boat needs to flap down for more drag on the sails to develop lift and speed. As the wind increases, the flap needs to straighten out so the drag decrease and the boat can achieve greater speed.

As usual, I have three settings for shroud tension in light, medium and heavy air. The vertical shrouds (V1s or cap shrouds) should be soft in light air, medium in moderate winds, and tight in big breezes. In light air, I tension the verticals just enough so there is some movement in the leeward shroud when the boat is fully trimmed upwind. In moderate breeze I use more rig tension so the leeward shroud moves only at the top end of that breeze. Once the boat has all the power it needs in heavier air, the rig should be tight enough so the leeward shroud doesn’t move at all.

I also change rig tension based on roughness of the water. For example, if the breeze is moderate but the sea state is rough, I may lean toward a light-air set up with looser shrouds. On the other hand, if the breeze is moderate and the water is very flat, I may go with a tighter, heavy-air set up.

The diagonal shrouds control sideways bend of the mast. You want the mast straight in most conditions, but in light air the middle of the mast should have some leeward sag. To gauge this, sight up the mainsail track from the boom to the top of the mast, looking for roughly one or (a maximum of) two inches of even sag up the mast. This keeps the main from becoming too round forward and helps the boat generate more energy in the slot in light air.

How much “pre-bend” should you sail with, and what’s the best way to get pre-bend in the mast?

Pre-bend is the amount of mast bend you have at the dock before you hoist your sails. It is created by a combination of factors, including the mast step location, the position of the mast at the deck and headstay length. Boats that have swept-aft spreaders can also achieve pre-bend by adding shroud tension.

The ideal amount of pre-bend for any boat is a function of mainsail shape just aft of the mast. The goal is to get the proper pre-bend so in light winds the main is not too round up front and in big breeze the sail does not get too flat.

To evaluate pre-bend, I like to set the main up in winds of 10 to 15 knots. With moderate backstay, my goal is to have all the mainsail draft stripes coming off the mast at the same angle. If the top stripe is round (wider angle) and the bottom stripe is straight (narrower angle), then there is too much pre-bend and the step should go forward. If the bottom of the main is round and the top is flat, the step should move aft to get more pre-bend.

Most boats are fast with the mast at maximum J measurement (measured from headstay to the front face of the mast) so we usually try to lock the mast at the deck and adjust pre-bend with either the headstay turnbuckle or the position of the mast step.

On one-designs, the only time I change he pre-bend is in extreme conditions. If it’s very light, I like moving the mast step aft to help flatten the entry of the main; in big winds I move the step forward to help the main keep is shape with maximum backstay tension. If the step is too far aft in big breeze the mast will over-bed. This creates a crinkle from the clew to mid-mast, and the main will just luff.

Are there any inherent tuning differences between one-designs and bigger boats?

The great thin about one-design sailing is the boats are equal and speed differences come from the sailors, sails and rig adjustments. However, this means one-design boats need more tuning changes than larger boats.

Many smaller boats have their own tricks that doesn’t work so well on larger boats. But in almost every boat, no matter what the size, you want a softer rig for light wind and a tighter rig in more breeze.

Big boats are able to generate a lot of their own apparent wind from the height of the mast, and this loads the rig up much faster than on smaller boats. Usually most of the shrouds stay set on larger boats (except for the headstay and backstay), but there are other tuning controls you don’t find on smaller boats. For example, some larger boats use a hydraulic mast step so they can lift or drop the mast to change rig tension.

Like a number of boats, the popular lightning uses blocks at deck level to induce or limit mast bend. You might think you should put more mast blocks behind the mast in heavy air to get more bend and flatter sails.

In fact, the opposite is usually true. In heavy air you need to pull hard on the backstay to straighten the headstay. If you have too many blocks behind the mast, it will bend too much and the mainsail will be over-flattened.

So when it’s windy you usually need to put more blocks in front so you can pull hard on the backstay without getting too much bend. In light air, put more blocks behind the mast so you get enough bend without pulling too hard on the backstay.

Do you tune a carbon mast differently than an aluminum mast?

Carbon masts seem less sensitive to changes in wind speed than aluminum masts. I think the carbon’s panel stiffness has a lot to do with how often the shrouds need to be adjusted. A soft aluminum rig needs constant tuning of the diagonal shrouds as the wind increases (or decreases), while a typical carbon mast is much more forgiving. The carbon rig has more range; we see the same thing in carbon sails.

What are some common tuning mistakes that racing sailors make, and how can they correct these?

Many boats I sail have the shrouds to tight for light-air (and even moderate-air) sailing. People worry that if the shrouds are too loose the rig will come down, but safety is not a problem if you are careful.

I start every day with the rig at its “base” setting (the shroud tension that makes the mast straight in 10 to 15 knots of wind). Then I add or take off turns based on the wind and sea conditions for that day. At the end of the day I always put the rig back to the base setting so I’m ready for the next day.

This system works best if you keep a tuning log and have a good understanding of your base settings. Measure everything and keep track of the changes you make. In light air, find a set-up where you are fast and record how many turns you let off from your base settings for the headstay, V1, D1, D2, and backstay. Then do the same in heavy air and record how many turns you added.

The main goal of tuning your rig is to go fast. But are there safety issues sailors should watch out for?
One common problem is making the diagonal shrouds too tight relative to the cap shrouds. This is a safety issue because if the diagonals are tight and the caps (verticals) are loose in comparison, the top of the mast will fall off to leeward; if it goes to far it will break.

Another concern is releasing the backstay (or running backstays) too far. This can cause the mast to “invert” or bend forward, which is the wrong way. If you keep the mast straight side to side with a moderate bend for and aft, the rig will be safe and should be able to sail in almost any condition.

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