David Thomas not only designed the Sigma 33 but also won the National Championship and many other trophies in his own boat Circe. This article was written before the class adopted Genesis sails. No attempt has been made to edit or update it because most of the advice still applies, but the accepted wisdom is that less prebend is needed with a Genesis main as sail stretch is less of a problem than it was with Dacron!
Getting the best out of your Sigma 33 by
David Thomas
(first published in Yachtimg
World, December 1990)
When a Sigma 33 race starts, the winner is going to be among the first five yachts over the line. The formula for a win is simply a fast, well-tuned and crewed boat and good starting tactics!
The moderate displacement hull of the Sigma 33 was designed to have competitive performance under IOR. To counteract the IOR tendency to reward moderate stability characteristics, a very easily driven hull was drawn with a moderate sail area to drive it without too great a heeling force. The result is a yacht that quickly accelerates to near her optimum speed and then takes a lot of concentration and persistence to find the extra edge.
The speed difference across the fleet is quite small and so the back does not lag too far behind. There are opportunities for all to see what the boys at the front are doing. I often advise Sigma sailors that the best instrument they can have on board is a good pair of binoculars to study the rig and sail settings of the leaders.
Having collected your brand new Sigma and added the statutory safety equipment. she is ready to sail - not to race. There are rites to perfom on her rigging and sails before that. There are various theories on mast rake. Tony Ashmead, RORC chief measurer, raced his Sigma with her mast raked slightly forward. She went round the race course as fast as the best. Perhaps she would have gone faster with her mast raked aft. That is the way most of the fast boats rig.
On Circe we carry 15-18 in (38-46cm) of rake measured with the main halyard weighted at the gooseneck. It is essential when performing this check to have enough weight (people) in the cockpit to put the boat on level fore and aft trim in smooth water. It also calls for an extra 1.5 in (4 cm) toggle to lengthen the forestay. The mast must be straight with caps and lowers slack. Pre-bend will alter the readings.
Pre-bend is now applied to the mast by tightening the cap shrouds with the lowers completely slack. Continue tensioning the caps until the spreaders push the centre of the mast forward 6 in (15 cm) from the straight line. Now use the lowers to pull 3-4 in (8-10 cm) back, leaving a pre-bend of 2-3 in (6-8 cm) which should suit a new or first season mainsail.
Next job is the backstay. With the mast raked and pre-bent and the backstay rigging screw (above the tensioning system) fully released, there will probably be little, if any, adjustment for the lever to take up and bend the mast further. To remedy this, fit a shorter lower strop. Read class rule 8.11. The aim is to have the back stay just firmly tight with the lever fully relaxed, leaving the full travel for adjustments as the wind increases. On really heavy days the backstay rigging screw can be wound down and the forestay rigging screw tightened to help keep it tight.
Now is the time to test the newly tuned rig. The first test might sound cruel but it is effective. A calm day is needed. The mainsail is hoisted to the black band (check with binoculars and mark the halyard). The mast is bent to maximum backstay tension. Cunningham and foot flattening are applied to maximum. Mainsheet is tightened and finally kicker is tightened until it just begins to bend the lower panel of the mast. Look up. The mainsail should be a completely flat pancake, no flow anywhere. If there is flow left behind the mast, remove it with more pre-bend. If there are diagonal creases radiating from the clew to the mast, remove them by reducing the pre-bend.
Now look at the standing rigging. If there is any slack in the cap shrouds, tension them, half a turn at a time, always keeping careful count, until they are just tight. Release all the tensioners and go to the forestay. Holding the forestay at shoulder height, swing aft with all your weight. The stay should not move more than 1.5 in (4 cm). You now have a rig that will suit average conditions. Slackening or tightening the forestay by three turns can cope with extremes in both directions, but remember that this must be done before the start of a race, for no adjustment is allowed during the race.
Rigging will continue to stretch throughout the season and the caps and forestay may need half a turn every six weeks or so. As the mainsail gets older, it also gets fuller in depth and camber. More pre-bend is gradually called for to take care of this. Repeat the calm weather mainsheet test if in doubt.
Your mainsail is your main sail. It is always set. Running or beating, full or reefed, a badly set mainsail is a boat speed disaster. There is a book's worth to be written about mainsail trimming alone, but the basic advice is to have a really attentive mainsheet trimmer who concentrates on it full time and treats it as a mechanic does a racing engine. Never over-tension any of its controls, particularly the mainsheet and the kicker. If boat speed falls off, ease everything and start again.
Now the headsails. Dacron sails take quite a long time to reach their optimum shape, perhaps five to six races. During this time they are sensitive to luff tension and leechline control. There is only one place from which to study a No 1 or 2 genoa and that is about halfway along the foredeck. From here you look up to where maximum camber should be. There are stripes on the sail to help you with the picture. Have the genoa halyard manned and then see how the flow moves backwards and forwards as the tension is varied. At the same time tune the genoa sheet fairleads until all the luff telltales break in unison.
On the brand new sail, if the leech flutters it probably means the halyard needs tightening. Only use the leechline as a last resort and after first giving it a good stretch of its own. Release the leechline at the start of each day's sailing and then retension it if necessary. When the genoa is settled and you can identify its average halyard tension, make a permanent black mark on the forestay fairing as high as you can reach above the pulpit. Then mark each sail in its medium halyard tension state against this mark. As wind strength varies, the halyard tension can be adjusted by sighting against the forestay mark. The situation is always up there in full view. It also helps a lot when rehoisting after a spinnaker leg.
With the rig tuned and the sails set, responsibility passes to the crew - in which I include th helmsman. On Circe we are lucky in having a regular team with regular substitutes. We have three helmsmen - all in the same family! My constant exhortation is for concentration. My two sons have to concentrate 100 per cent on trimming the mainsail and genoa and at the same time, 100 per cent on the tactical situation.
Choosing the right sail combination for the start is critical. Uffa Fox's advice still holds. "Set the right amount of sail for the lulls." With the No 1 genoa an inch above the forestay mark and the genoa fairlead one or even two holes back from its medium position, with the mast at full backstay bend and the mainsail flattened at 100 per cent, the mainsheet traveller at the end of the track and the trimmer ready to ease just four or five inches in the slams, the Sigma will carry full rig in smooth water and 22-23 knots of apparent wind.
This technique needs a lot of practice. Once the edge is lost it can take minutes to get things back in order. In a large fleet or when short tacking, it pays to use the No 2 genoa to give greater flexibility to manoeuvre. Do not bother with a No 1 and reefed mainsail, except as a temporary 'holding' move to finish a leg. Whichever combination you choose, the aim is to keep speed up and heel down.
If the spinnaker pole is not being retrimmed as often as the main and genoa sheets were on the beat, you are not paying enough attention. Windshifts are just as important on a run as a beat. Gybing as a matter of course, instead of in emergency, should be the drill. Lots of gybing should speed you up.
Broaching is a great time waster on the race course. It should not be necessary to broach provided the spinnaker pole is kept far enough back from the forestay as the wind increases. Spinnaker reaching with the pole on the forestay in fresh conditions is asking for trouble. It is also slow. Keep the pole back at 20-25 degrees. You will occasionally round up, but you will find it easy to bear away again, provided nobody lets the pole forward. Have one hand on the kicker, ready to ease it when the helmsman squeals!
Of course, Circe, as 'the designer's boat,' might be thought to be a special with a super light hull, superfast keel and hand-stitched genoas. Our only modification has been to raise the mainsheet track on two wooden packing pieces to stop the control lines fouling. Otheriwse, she is strictly off the shelf. You have all our tuning secrets, so come and get us!