While lightweight is important to preserve such performance qualities as a high righting moment and low pitching moment, its 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.
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.
"Once we make sure the mast is in the middle of the boat (see sidebarGetting 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 its about the same distance from the top bottle screw to the bottomwe 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."
"Weve 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 boats 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 TuningWhether youre tuning a rig with one set of spreaders or five, there are two initial objectives:
If you dont 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 isnt loadedlet off the backstay and vang, and make sure the other halyards arent 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 youre 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 youre 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 youre 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 its 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, youll have to respond by adjusting the shrouds. If you have a single-spreader rig and the mast is bowed to port, youve 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 shroudsso adjust accordingly. The more spreaders in the rig, the more adjustments that may be necessary, but the concept doesnt changestart with a mast thats centered and in column, and youre well on your way to tuning the rig for performance.
|Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)|