Setting it Straight: Viper Rig Tuning - Viper 640 International Class Association

By Jackson Benvenutti, North Sails One Design

If you haven’t noticed yet, your Viper mast is about as noodly as masts come. This makes it tricky to properly set-up your mast straight and in column; but here is how I do it. Note – it’s important to not skip any steps or cut any corners if you really want to have your rig set up properly while minimizing any doubt. Take your time, and be methodical:

  1. With the mast out of the boat, make sure your headstay is set to the correct length for the tuning guide for your sails. For North sails, this length is set to the class maximum of 7588mm. It’s important to get this measurement as accurate as possible, and I’ve found discrepancies in the measurements unless you actually take the headstay off the rig, lay it down on a flat surface, pull it taut, and measure from the bearing points of each end per the class rules. Make sure to lock your headstay length properly with the lock nut and rigging tape after becoming confident with the proper length.
  2. Find some bungee cord to attach between your spreader tips so you can accurately measure the spreader deflection. It’s important to remember to apply slight downward pressure on the tips of the spreaders when measuring (from mast top to bottom), so that you measure the realistic difference from the bungee cord to the back of the mast track. Due to the nature of the spreader and upper shroud rigging, the shrouds will slightly lift the tips of the spreaders when they are not loaded up as if they are when your mast is rigged in the boat. Applying slight downward pressure ensures you are getting a more accurate measurement for when the shrouds are loaded up and pulling the spreader tips down. This measurement is very important, as it will affect the prebend in the rig.
    The final check of this measurement should be done with a prebend checking device that runs up your mast track. You can measure the prebend as you run through the rig change steps in your tuning guide for future reference (and collect some good data). Do this by hoisting a prebend checker in your mast track using the spinnaker halyard and a line on the bottom so you can pull it back down. Then pull your main halyard tight and into the bottom of the track. Hoist the prebend checker just above the spreaders and slide it up and down until you reach the max bend location. Record the numbers as you run through each step up and down in your tuning guide (a good rule of thumb is the 2:1 ratio, meaning that for every 2 turns you put on your upper shrouds, add 1 turn to your lowers).
  3. Step your mast and tune the boat for your base settings per your tuning guide.
  4. To get the mast in column (tip directly over the butt):
    1. First, make sure your boat is not leaning to one side or the other. Your iphone has a handy-dandy level located in the compass app, just swipe it sideways once it’s open and you’ll get to the level. Place the level on the rudder bracket and adjust the boat accordingly—usually by spinning the trailer one way or the other.
    2. Once the boat is level, find a heavy weight to hang from the spinnaker halyard and make sure you pull the knot tight. A bucket with some tools and/or water bottles will work fine, just make sure it has a good amount of weight in it so that it pulls that halyard tight. The heavy weight hanging on the halyard will make sure you have a constant force on the line for accurate measuring.
    3. Create a mark on each rail with a sharpie, equidistant from the headstay pin. I like to make my marks close to in-line with the front of the mast. Make sure your marks are not so far back that spreaders will interfere with the spinnaker halyard.
    4. Now, with the weight hanging from the spinnaker halyard, bring the halyard to the mark on the rail. Mark the halyard with a sharpie right where the line reaches the deck. I like to lay the marker flat on the deck, and mark the halyard with the sharpie in that position. You could also mark the halyard where the rail ends.
    5. After you’ve marked the halyard on one side of the boat for reference, swing the halyard and weight around the front of the boat to your mark on the other rail. This part is important and tedious, it’s crucial that you don’t unload the halyard or allow the line to spin and twist up, or you might not get an accurate measurement.
    6. Adjust the upper shrouds equally (ie – if you take 2 turns off the port shroud, add 2 turns to the starboard shroud) until your reference mark on the halyard reaches the same height at your marks on both rails. Once you’re satisfied that they are the same, your mast is now in column! Congrats.
  5. Adjust your lowers properly by following the steps in your tuning guide. This will get you in the ballpark, but you’ll really need to go sailing and make sure that the side bend in the mast is equal on starboard and port by sighting up the mast while sailing properly upwind.
  6. Hike hard, and sail fast!