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How to Tune

Author??? gives the beginner an introduction to tuning, in a simple step-by-step process - Summer 2004
Getting your head round tuning your dinghy can seem impossible if you're a beginner - particularly if you don't understand the lingo or know your spreaders from your shrouds. We guide you though the basic process of tweaking...

Articles on boat tuning tend to assume you already have a certain level of knowledge - but that's no help if you've never done it before. So in this article we will strip away the jargon and give you a simple step-by-step guide on tuning your dinghy, so by the end you'll understand how to set up your boat with a basic rig configuration. It is about 'how' and not 'why' - think of it as tuning by numbers.

We want to start by exploding two commonly held myths. First is that the only reason to tune your boat is to make it go faster. While it's true that tuning your boat will make you go faster, a properly tuned boat will also be better balanced, more forgiving in the gusts generally easier and more pleasurable to sail, particularly in stronger winds. Go to any sailing club on a moderately windy afternoon and you will see many sailors struggling to stay in control of their boats, more often than not, a badly tuned boat is the main reason for this, not poor sailing skills.

Myth two is that tuning is a complicated and intuitive process. The best kept secret about tuning is that there is no secret. Strip away the jargon and it is simply the application of some standard measurements to the rig and it's position in the boat.

At it's simplest level, tuning is setting a rig up to the optimum combination of three measurements:
  1. Rig tension. This is the tension in your standing rigging. It is measured on either the jib luff wire or on the shroud.
  2. Mast rake. With rig tension pulled on, mast rake is the distance from the tip of the mast to a fixed point at the transom of the boat.
  3. Pre-bend. With rig tension on, your pre-bend is the distance between the rear of the mast at the spreader bracket and the main halyard - when this is stretched taut to the gooseneck.
Before you get down to the nitty-gritty of physically tuning the boat, check that you have everything you need:
  • Obtain a tuning guide
  • Get a helping hand, this is a two-man job.
  • Give yourself a bit of space - at some point you will need to turn the boat over to adjust the spreader.
  • Set aside a little time - one to two hours should be adequate if you have not done this before.
  • Make sure you have the right tools. You will need to adjust the angle of your spreaders and, depending on your spreader bracket fittings, this will normally require pliers/spanner and screwdriver. If the spreaders have not been touched for sometime the adjustment system may have corroded up. Some WD40 could be useful here. You should also have a tape measure long enough to measure mast rake, plus two bits of thin rope (max 4mm diameter) -one long enough to tie across your shrouds at deck level and the other long enough to tie across the spreader tips. Then you'll need a rig tension gauge and a waterproof marker pen.

Course Tuning

This is the first part of the tuning process, which roughly sets up the rig in the boat.
  1. First measure the mast heel position. In most cases the mast heel needs to be as far forward in it's rack as possible. The class tuning guide should help you here, if not give your sailmaker a call and they should be able to help you.
  2. Next adjust the spreader length. Measure the spreader length from the side of the mast to the shroud and adjust to the length shown in the tuning guide on the web forum. If there is a range, the general rule is to go for the shorter and if you are light and the longer if you are a bit porkier.
  3. Step the mast and pull the jib up.
  4. Ensure that any mast retainer is off - i.e. uncleat your strut/ram or lowers so that the mast is free to move at deck level in the step.
  5. Now slowly pull on the rig tension. As one person does this, the other should be measuring the tension with the tension gauge. When the target tension is achieved (as defined by the tuning guide) cleat the rig tension.
  6. Pull the tape measure to the top of the mast on the main halyard and cleat it.
  7. Measure the mast rake. This is where the tuning really starts. If your rake measurement is larger than the measurement you are trying to achieve from the tuning guide, the mast is too upright and needs to be angled (raked) back by adjusting the shrouds. Conversely, if your measurement is less you are angled too far back you will need to free off tension on the shrouds.
  8. Pull the rig tension back on and repeat steps five to seven until you get to a position where at the target tension the rake is within one or two inches of what you are trying to achieve on your guide. Once you have achieved this, make a rough note of the rig tension position by putting a small mark on the mast against a reference point on the jib halyard.
Making the rig symmetrical

Having got the rig roughly set up, we now need to ensure that it is set up symmetrically in the boat. So, first pull the rig tension back onto your approximate mark on the for deck post. Next tie one of your pieces of rope across the shroud plates - when doing this, make sure it is taut and not being pulled out of it's natural lie by the boom.

Now turn the boat on it's side (tie in your boom or better still remove it).
Check that the spreaders are at an equal height on the shrouds. Cleat the main halyard and pull it taut down to one spreader end. Grip the halyard tight between the thumb and forefinger at this position and arc it across to the other shroud. This will show you if your spreader heights are different. Move one or both spreader ends up or down the shrouds until they are at equal heights.

Tie the other piece of rope across the spreaders. We now want to ensure that both spreaders are at equal angles. To do this, look down the mast from the mast tip to see how the rope across the shroud base lines up against the rope across the spreaders. If the spreaders are at equal angles the ropes will be parallel to each other. If they are not parallel one spreader will need to be angled further back using the adjustment system at the spreader bracket until the ropes are parallel.

To decide which spreader to move and in which direction, first measure the pre-bend. This is done by pulling the main halyard to the gooseneck and pulling it tight and then measuring the distance from the halyard to the rear of the mast at spreader bracket level. If the tuning guide specifies that you should be measuring deflection, you can measure out to the rope tied across the spreaders. If the measurement you have is less than the measurement in the tuning guide you will need to move the spreader that is angled further forward back and vice versa. To adjust the spreaders you might need to ease the rig tension but remember to pull it back on again before you re-sight down the mast.

Now check that the mast is in the column - i.e. it is not bending off to one side. To do this put the boat upright on it's trolley again and sight up the mast track. If it does not bend off to one side, great. If it does, we need to correct this. This can be done by lowering or raising the shroud on one side.


Fine Tuning

To fine tune the rig all you do is make small incremental adjustments to rake and spreader angles until, at the prescribed rig tension, you have the right rake and pre bend measurements.

First pull on the rig tension until you get the correct rig tension. Then measure both rake and pre bend. Once you have measured these, consider what you need to adjust in terms of spreader angle and shroud adjustment to get the desired pre bend and rake. Unfortunately, as you change one variable you also change the other.
  • Angle spreaders back - increases pre bend and decreases rake measurement.
  • Angle spreaders forward - decreases pre bend and increases mast rake measurement.
  • Pull shrouds down - decreases rake measurement and increases pre bend.
  • Raise shrouds up - increases rake measurement and decreases pre bend.
Only make small changes at a time and after each change re-measure pre bend and rake. Unfortunately this part of the process does involve pulling the tape to the top of the mast and then dropping it and turning the boat over to measure the pre bend several times, but though an iterative process you should quickly get closer to your desired measurements. You should be able to get to within inch of the right rake measurement.
Finally mark everything off with a marker pen so that you can replicate those magic settings you've worked so hard to find: mark off the rig tension position on the mast, mark off the shroud tension on the mast step post and similarly for the lowers.

The above is a very quick guide to tuning but for a more detailed account refer to Mike Calvert's previous article on this subject.


See also:
      Setting up the mast - Graham Williamson
      Calibrating the Rig - Graham Williamson