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Old 08-30-2000
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Rig-Tune Innovations on the 1D35

 
Light, strong, adjustable rigs, like those on the 1D35 are leading to rig-tune innovations.
 
Over the last few years, the popularity of swept-spreader, carbon-fiber masts without runners has continued to grow among both racing and cruising designs around the world. The simplicity and safety of these spars stand in contrast to lightweight aluminum masts that need runners and checkstays for support, and are thus prone to breakage when mishandled. The intrinsic stiffness of the carbon-fiber mast, coupled with the swept-spreader design of the standing rigging, has created a rig system that is at once light, strong, and safe.

While lightweight is important to preserve such performance qualities as a high righting moment and low pitching moment, it’s also important that the operators understand how the mast is tuned to optimize sail shape for varied conditions. Unlike a spar with runners and checkstays, the bend and stiffness of carbon swept-spreader spars cannot be dynamically adjusted while sailing, so set-up and tuning becomes critical.

 
Reference marks on the luff of the headsail allow the sailors on this boat to know how much headstay tension they have.
 
The mast in the 1D35 Class is unique among this genre of rigs because it has slightly more flexibility in dynamic adjustment due to the lack of a permanent backstay and the addition a hydraulically adjustable headstay. The reason for this is that the racing rules permit dynamic adjustment of the rig in only one direction—forward or aft. The designers at Nelson/Marek, along with Scott Ferguson at Hall Spars, engineered a solution where the sweep angle on the spreaders allows the spar adequate support in the aft direction, yet also allows the headstay to be adjusted to vary its sag, which in turn can power up the small non-overlapping headsails this boat uses. This geometry means that as the cap shrouds (upper shrouds) are tightened, the rig is given more rake, the headstay is lengthened for a given amount of sag, and the diagonal shrouds are used to control mast bend, and to a lesser extent mast stiffness as well. Adding tension to the headstay through hydraulic adjustment not only reduces sag, but also puts tension on the vertical shrouds and the diagonals as they restrict the compressive motion of the spar.

For an example of how to optimize the adjustment of this rig system, we asked Nick Worth to share his thoughts on how he tunes the rig on Widowmaker to winning form. He and his wife Tina led their team to victory last weekend in the 1D35 Great Lakes Championship, beating 21 other boats in one of the more competitive classes in the US. The event was held over three days in Holland, MI, with conditions varying from four to 14 knots of wind.

 
The marks on the spreader help the jib trimmer know where to trim the jib for a given rig tune.
 
"We’re actually lucky, because most of our crew has sailed competitively on boats with small jibs, so we’re acutely aware of how important rig tune is to performance," said Worth. "Since we travel with the boat so much, it’s important that we are able to reproduce our rig settings, which have proven to be fast, so we’ve devised a system to calibrate the rake through shroud settings, and mast bend through diagonal tension."

"Once we make sure the mast is in the middle of the boat (see sidebar—Getting Started with Rig Tuning), we tighten the shrouds down to our pre-determined rake point. This leaves about a centimeter or so of throw left on the turnbuckle. Hall Rigging has done a nice job of matching the rod lengths and Carroll Marine (the 1D35 builder) has built a symmetrical boat, so that it’s about the same distance from the top bottle screw to the bottom—we measure this gap in millimeters and leave it at that setting for the entire wind range."

The next step, according to Worth, is in altering the diagonal tensions for the given wind conditions of the race. "D1" is the term used to refer to the lower diagonal [from the chainplate to the base of the lower spreader], and "D2" the term for the upper diagonal on this two-spreader spar. "Our new sails have a little less luff curve than our last set, so we went with less pre-bend, about as much a Mumm 30," said Worth. "We did this by putting a little less rake in, so that meant fewer turns on the shrouds. Even though less rake means less weather helm, in light air, it's an acceptable trade off.  For the mast bend, we just set the D tensions until the main looks right for the conditions. For the light air, the Ds are firm to keep the mast straight and the mainsail deep in shape. As the breeze increases and we want to have more bend to flatten the sail, we ease the D2s at about twice the rate as the D1s (since the turnbuckles for the D2s are smaller for the smaller-size rod), with maybe several turns total in the range of adjustment."

 
With the outhaul maxed and the headstay at 3,500 pounds, the mainsail blades out nicely on a 1D35.
 
While easing the Ds will allow the mast to bend and the main to flatten, analogous to a checkstay on a spar with runners, that adjustment can also have the effect of reducing headstay tension, though on the 1D35 this is hydraulically controlled. The maximum tension that can be put on the headstay is about 4,000 pounds, but in very breezy conditions the boat seems to require more than that to give the jib a straight entry, so there’s actually a lower limit to the amount the Ds should be eased, with the main flattened and twisted to depower.

"We’ve had a variety of boats, including a J/120 and a Mumm 30, and we really love the 1D35," said Worth. "The size is great for us, the boat’s really responsive, the ease of transport makes it easy to go to different regattas, and the ability to shift gears through the wind ranges with this spar makes it really fun to sail."

Getting Started with Rig Tuning

Whether you’re tuning a rig with one set of spreaders or five, there are two initial objectives:

  1. centering the mast in the boat
  2. getting it in column.

If you don’t have a tape measure to make sure that the top of the mast is equidistant from each side of the boat, you can use your main halyard. Before you start, make sure that the rig isn’t loaded—let off the backstay and vang, and make sure the other halyards aren’t tensioned. Then, simply free the main halyard and stretch it down to the toerail at a fixed point just aft or even with the chainplate. Hold your end of the halyard at this place while someone tensions the other end and cleats it. You want only as much tension as it takes to produce just a little resistance on your end of the line. Then mark the spot where you are measuring on the toerail. (You can use a pencil to do this.) Now, walk the halyard over to the other side of the boat and take a similar measurement to the toerail using the same tension on the halyard. If you’re not sure that your measurement is in the right place on the rail, simply stretch a line from the head stay back to your original mark, and use that to ensure that you’re measuring to identical spots on the toerail. If the halyard reaches the toerail on each side of the boat with equal effort, then the top of the mast is equidistant from each side, and you’re ready to continue tuning. If more tension is needed to extend the halyard to the toerail on the port side than on the starboard side, the top of the mast is slightly askew to starboard, which means it’s either leaning or out of column.

Getting your mast in column means ensuring that the mast is straight. Start by sighting up the luff groove or sail track on the aft side of the mast. Depending upon where the bend or curve is, you’ll have to respond by adjusting the shrouds. If you have a single-spreader rig and the mast is bowed to port, you’ve either got too much tension on the port-side lower shroud, too little on the starboard-side lower, or an inverse of this situation on the upper or cap shrouds—so adjust accordingly. The more spreaders in the rig, the more adjustments that may be necessary, but the concept doesn’t change—start with a mast that’s centered and in column, and you’re well on your way to tuning the rig for performance.