Graduate Dinghy Association

Tuning Tips: Part 1

Whether you are updating an old Graduate, or fitting out a new hull, the information contained in here should provide a basis for a successful racing dinghy. The measurements given should be taken as a starting point, from which fine adjustments can be made to suit the individual. In some cases, precise settings cannot be given due to the scope for variation in hull/rig measurements in the class rules, so it is advisable to check measurements with those of other boats whenever possible, as a further reference.
To prevent this piece becoming a large book, it concentrates as much as possible on measurements and advice specifically for the Graduate, how things should be done, rather than why. To find out the principles of rig tuning, I suggest that you read books on the subject. A book which explains tuning fairly simply, and in logical steps is 'Tuning your racing dinghy', by Lawrie Smith. Another useful source of information is magazine articles such as those published in Yachts and Yachting, which usually concentrate on one particular area of boat tuning.
When explaining the things which will make your boat go faster, we will presume that certain points are in order:

(1) The hull is sound and not likely to give under the stresses imposed when sailing.

(2) All fittings are securely fixed (preferably bolted) to the boat, and will not pull off or move.

(3) The boat does not have a wooden mast, as this makes rig tuning impossible.

(4) The boat owner is a member of the class association and has a current racing certificate for the boat, without which it should not be raced.

Before you start trying to set your boat up to go faster, there are a few basic points which you should consider. Without this preparation any time you spend tuning the boat may well be wasted.
First you should make sure that the boat is fitted out symmetrically about it's centreline. Most importantly, the shroud plates should be equal distances from the stem fitting. and the mast step should be located the same distance from either shroud plate (i.e. exactly on the centreline).
Probably the most important (and most ignored) area of the boat is the bit that goes in the water. The hull finish is not as important to boatspeed as most people think, as long as the hull is fair and sound, a smooth paint finish is not necessary. However the centreboard and rudder must be exactly parallel to each other (i.e. in the same plane). If they are out of line the foils will work against each other causing excessive drag, and slowing the boat considerably.
For this reason, if for no other, the centreboard and rudder must be as tight a fit as possible in the case and stock respectively, so that they cannot move sideways at all under pressure, and so become out of line. It is also a good idea to check that the centreboard can go fully down (just forward of vertical) otherwise the boat will point badly when beating.
Regarding the rig. If there's anything seriously wrong here, it can usually be spotted easily, so it doesn't need to be covered here in any detail. However, do make sure that the mast and boom are not permanently bent (which is out of class anyway) and that the shrouds are both the same length. Finally, make sure that the mast is a tight fit in the mast step, and cannot be twisted at all. To prevent any movement here, tighten the mast step bolts immediately in front and behind the mast heel. If the mast is very loose in the step, packing pieces should be fitted inside the step either side of the mast heel.
Now that any basic faults with your boat have been corrected, you can begin setting the boat up. Starting with the rig, the first thing to establish is the mast rake, because if you change the rake, everything else (such as spreader deflection, jib sheeting angle, etc.) changes as well. Mast rake is largely a matter of personal preference; although everyone sails with the mast raked slightly aft of vertical, there are visible differences in rake between the boats at the front of the fleet. The best way to get roughly the right mast rake is by hanging a weight from the main halyard, when the boat is level fore and aft and the jib halyard is tensioned a little. The main halyard should then hang 18cm aft of the mast at gooseneck height. As a further guide, when sailing in light weather, the boom should be horizontal or sloping slightly upwards towards the aft end. Don't feel that you have to keep strictly to these guidelines; if the rig looks or 'feels' wrong when you're sailing, don't be afraid to change the rake a little at this stage.
Having decided on a mast rake position, you can now start work on other parts of the rig. Probably the first thing that people think of when you mention tuning is the spreaders. Ideally you should have screw adjusters fitted so that the spreaders can be positioned accurately:
However it you don't have that luxury, the spreaders will have to be set by estimating their optimum position, bearing in mind how full your sails are, what crew weight will be in the boat, and how stiff the mast section is to begin with. As an example, with a Proctor 'C' section mast (the most common section in the Graduate fleet), the spreaders should be set so that they deflect the shroud forwards 4cm, and outwards 2cm from it's straight line position, when sailing with a crew weight of about 20 stone. (Note, for most Graduate masts it is not advisable to deflect the shroud outwards more than 4cm, even for heavy crew weights, because when the jib halyard is tensioned, the mast will tend to bend sideways uncontrollably, causing a loss of power, particularly when reaching). As with the mast rake, these spreader settings are only guidelines, which will vary depending on how full your sails are (flatter sails require less deflection and v.v.). lighter crew weights and boats with stiff masts (Proctor kappa) and/or full sails will need shorter spreaders, raked further aft, the opposite applying to boats with bendy masts (Needlespar, and Proctor Alpha or Lamda) and/or flat sails.
Simply bolting the spreaders like this is inaccurate and difficult to do. If the screw adjusters mentioned previously are fitted to the spreaders, a lot of these problems can be avoided. Before setting the spreader angle you should cut the spreaders to the required length, so that the outwards deflection is set (as above). To set the spreaders with the right amount of fore and aft deflection, you ideally need to go sailing in medium winds, where both helm and crew are sitting on the sidedeck, but the boat is not overpowered. Before you go out, both spreaders should be set to the same angle, so that the mast doesn't bend differently on either tack. To do this put the mast up without the shrouds attached to the spreaders, arid use the screw adjusters to set the two spreaders so that the aft edge of the spreader just touches the shroud. The spreader ends can now be reconnected, and the boat rigged. Tension the jib halyard fully (you should get 400lbs of tension on the shrouds), make sure that the main halyard is tight enough to remove any small wrinkles from the luff of the mainsail. Tension the outhaul, so that a crease begins to appear along the foot of the sail. You should now sail the boat closehauled, and, without tensioning the kicking strap or cunningham, pull hard on the mainsheet until the leach of the mainsail becomes tight (the leach telltale at the top of the mainsail will stop streaming off the sail). The mainsail will probably now have large creases running (tom the clew to the mast at about spreader height.
It these creases don't appear, rake the spreaders aft until they do. You must now move the spreaders forward a little (say 2 turns on each adjuster), and tension the mainsheet again to see if the creases still appear. If they do, move the spreaders forward another 2 turns and check again. Continue this procedure until the creases just disappear. The mast is now bending the right amount to suit your mainsail. and the spreader adjusters can now be marked and left in this position. This spreader angle can only be improved further by making minor alterations for different wind strengths; for light winds the spreaders should be raked aft a little (and lengthened a little, if possible) and for heavy winds, they should be raked forwards more (and shortened). However such alterations make little difference to boatspeed and I suggest that you forget about them, at least to begin with.
The next point to consider is the jib sheeting position. A lot has been written on this subject in the last few years, and I suggest that you read about it elsewhere to get an understanding of the theories involved. However as a starting point, for the Graduate in particular, the jib fairlead should be 23cm inboard from the shroud and roughly 175cm from the stem fitting, where the jib is attached. The tack of the sail should be shackled here, within an inch of the very front of the boat, and should be secured close enough to the deck that when the sail is sheeted in, the foot touches the deck along most of its length. The jib halyard should also be tensioned, before the fairlead position is set.
Basically the sail is set correctly for medium winds when, as the boat is luffed gently above closehauled, the jib begins to back at the same moment all the way up the luff. If the lower part of the luff begins to back first, while the top is still full, then the jibsheeting position should be moved aft (or up) but if the upper part backs first move the sheeting position forwards (or downwards). Moving the fairlead fore and aft can then set the sheeting position for light and heavy winds.
Because of the need for easy adjustment of the fairlead position, and for a close sheeting angle, it is difficult to fix a track and fairlead (as found on other classes) in the right place. See the separate jib sheeting article for further details.