Pre-Tuning 2
Home Up


Last update, December 27, 2009


Page Two of Two

  1. Set the twist in the upper part of the mainsail. This is controlled by the vang as it changes the tension on the leech of the sail. I hope you get lucky as this can be a pain to get right. So, here is some information:

This is a solid hard vang. It has a big adjusting wheel and a lot of threads but it really has a small range of settings. As you try to increase twist (loosen the leech) the counterclockwise turning of the adjusting knot lengthens the vang driving the boom up. Because the mount to the boom is fixed, this lengthening pulls the mast toward the aft creating a convex curve in the mast centered on the boom gooseneck. Whew! We have no alternate adjustment for this. You can help. Design a vang that will re-reference; like a shock spring in the tubing. Good! The world will beat a path to your door.


Likewise, as you tighten and hence, shorten the vang, the mast will bulge forward. Generally, this is only for high wind tuning and all the effects are positive.

So, you now know the negative things to look for. Here are some photos to study for lessons in the "Good and Evil" of vang settings.


There is about a three turn range that will not effect the mast. You might get lucky. If not, here is how to handle it. It may take some time. Forget the bend for now.

You have set the boom close to centerline and the winch is fully close hauled. It is expected there will be little to no twist in the main in a calm room. Understand, as you lengthen the vang to introduce some twist, the boom rises and thereby, increases tension of the sheetline. This will defeat your effort. Think about it. So, as you go through the process of setting twist and/or re-referencing the vang, always reset the sheetline. Important!


Roll the boat over in the cradle. Set the vang so that you will have zero twist. The top batten of the sail will be parallel with the boom (not centerline). Now, if the mast is still straight and you let the sails out one bump on the TX stick, you will see the batten move away from parallel slightly. Good. If this happened for you, then this is the base setting. These angles will be greater in the water under some wind pressure.


Increase the twist till you have about 15 degrees off the boom at the top batten and one bump out. Is the mast bend starting to convex? What does that mean? The vang is too long and is pulling the mast. Right! If this is the case you want to re-reference the vang mount to the boom. Without changing the setting of the vang, move the mount forward toward the mast. You have two holes in the mount and boom. Move the aft screw to the forward hole. Drill another forward hole through the empty mount hole with a #50 bit. You can do this on the floor with the boom sheeted out.


How is the mast bend now? That should have relieved some or all of it. Did you reset the sheetline and are you one bump out? You getting the idea of re-referencing? Okay, the reverse will be true of a forward bow in the mast. Check the BST is still at 2 pounds. To a lesser degree than the sheetline, the BST is effected by the vang.


What you will notice is that there is a point in the vang connection that the adjusting wheel feels free and not harder to turn one way or the other. That is a neutral spot that will give you the range needed.


You just got 2 years of experience, all that we have and with over a dozen rigs built. There are a lot of words here but the procedure of setting the vang, if it is off, is simple and far easier for a two-handed person. Vern went to sleep at 19 above. Its okay, we are used to that.


Why twist? Lets don't get into it now...

  1. Set the twist in the jib. HEY! Don't leave now, this is easy. Adjust the topping lift to set a twist in the jib so the leech of the sail matches the leech of the main. You will find that it is easier to lift the aft end of the jib boom as you move the adjuster forward just a bit till you get the desire results.

  1. Install the lower/lower shrouds. These are optional and you can add these at a later time. They have not been mentioned till now for they were not wanted in the mix of rigging and pre-tuning.

The lower/lower shrouds, connected on a mount just above the main boom gooseneck, are designed to stabilize this portion of the mast against tensions of the lowers and to prevent the mast from moving forward by forces in or on the vang. Some consider this to be minimal compared to the aerodynamic drag they may produce.


Because of drag, we do not install them on light air rigs. However, it has been noted that sometimes there will be a lateral distortion in the lower portion of the mast. It is felt that this may be caused by downward tension of the other shrouds. These short shrouds will take care of that.

During the mast section you installed the mount and during the rig assembly prepared the connectors. Swage a loop of rigging wire through the mount on the mast. Install the connectors to the shroud rack as you have done before snug up the wire and swage it. The connectors should be in the center hole of the angled portion of the rack for a center mast position on the step. The rack was designed with these shrouds in mind if wanted. Whenever you move the mast in the future, move these connections in a like manner.


In set up at the lake, these shroud connections are the last step in rigging and pre-tune. You will not want these to influence any of your efforts. They are not needed in tuning and are only here to stabilize the lower mast. When you are done with everything, like the above items, connect the lower/lowers and snug them up. No pressure is needed. Now, roll the boat over one last time to make sure the connection did not change anything.

It is time to get wet!

"Wake up, Vern! This puppy is ready for the water."


Top of Page