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MERLIN ROCKET TUNING AND SAIL SETTING NOTES PART A. BASIC RIG TUNE Jib sheet fairleads The jib sheet fairleads should be organised so that, in conjunction with the correct sheet tension the clew is about 300 mm to the centreline with the sail set. (On older boats this might be greater). Fore and aft fairlead position is perhaps more critical, and in most boats the track position is fixed laterally, and can be trusted. A good starting point for fore and aft fairlead position is when an extension of the line of the sheet would meet the jib luff two thirds up the luff. With the leech setting correctly the foot should be almost creasing. If the fairlead is too far aft the foot will crease and flap. Very little adjustment is needed for different wind strengths once the right position has been established. Mark it. Mast rake Mast rake varies from boat to boat. If in doubt, set the boat level and establish rake of 300mm to 350 mm measured by hanging a weight on the main halyard and measuring rake at gunwhale level. This will be a safe starting point for light to moderate winds. If you have trouble levelling the boat use a plumb line or spirit level to set the stem vertical. With a raking rig you will need about 600mm of rake for windspeed 15-20 knots and about 900 mm of rake for 25-30 knots. This will vary appreciably according to crew weight / fitness, and sea conditions and may need to be adjusted frequently for the best performance. Spreaders Spreaders can safely be set to deflect the shrouds up to 30mm out from a straight line, and not pulling the shroud appreciably forwards or aft from a straight line. The stiffest masts will need less than this. With a normal rig tension the mast adopts between 30mm and 40mm of prebend. Strut / mast chocks / lower shrouds To set the strut / mast chocks / lower shrouds let the mast move freely to its natural prebend when you apply normal rig tension, and then set the strut (or chocks or lower shrouds) to firmly add support without changing the mast bend. This is a starting point around which to work in very small increments of adjustment. Rig tension The best guide for rig tension (applied using the either jib halyard or adjustable shrouds) is simply to ensure that the leeward shroud is never slack. This requires more tension in more wind, and if you care to take the trouble your speed will benefit. A deck-stepped mast requires a different approach which generally demands more tension in a given windstrength, and in particular to prebend the mast in light winds. Your normal minimum rig tension is the amount which puts prebend into the mast. NOTE : Because Merlin rigs vary so much in concept the above can only be a generalisation, and if you have doubts about the basic settings for your rig seek advice from your sailmaker or some other friendly, knowledgeable and trusted source. PART B. SAIL SETTINGS BATTENS Top Batten- Tension it only just tight enough to remove most localised wrinkles along the batten pocket. Once you have established a good working tension, you may not need to readjust for varying conditions. If your top batten is proving very hard to tack or gybe it is probably too tight in the pocket. Batten Care- You can safely leave the battens permanently fitted. If the top batten is tied in, knot the top batten ties securely before pushing the free ends back inside the batten pocket with a screwdriver to keep them secure and out of the way. A buckle or velcro tensioning system can be taped for long-term security. Most sails and the tuned battens supplied with them are fully compatible. The battens should not need adjusting for shape or flexibility. It can sometimes be advantageous to fit a stiffer top batten in very strong conditions. OUTHAUL Upwind - The clew should be pulled right out to the black band for extreme light winds or when you are overpowered. For normal light / moderate conditions it can pay to set it be 30 - 40 mm in from the band to give more power to the lower part of the sail. For flat water have the outhaul slightly tighter. Remember it can pay to ease it more for extra drive when sailing in choppy conditions. Offwind- a) In light or moderate winds. For any reach broader than a close fetch, the outhaul can be eased up to 100mm for extra sail fullness and power. On a dead run this makes less difference to boat speed. It makes most difference to boat speed when marginal planing or surfing conditions exist. b) In VERY strong winds . Only ease the outhaul if you can easily reach the string. You will have other priorities! CUNNINGHAM Upwind- a) In light and medium conditions:Pull only just enough tension to almost eliminate horizontal creases near the luff. Set like this the sail will develop its maximum power. It is frequently beneficial to leave the luff region of the sail with some horizontal creases, but in very light conditions the top batten is often easier to tack with a minute amount of mainsail luff tension applied. b) For stronger wind: Extra tension on the cunningham straightens and flattens the upper part of the leech, helping it twist more readily to spill unwanted power. The more cunningham tension you apply, the more easily the sail will twist open for a given gust of wind. The sail responds more quickly to gusts, but give less power. REMEMBER: More luff tension = less power, Less luff tension = more power. Offwind- In all wind conditions (and particularly if you are using extra luff tension to depower the sail for beating) - Release the cunningham completely. VANG (Kicking Strap) a) In light to moderate winds: Beating and Reaching - Allow enough sail twist for the tell tails on the upper leach to fly nicely. With too much sail twist the tell tails will stream too easily You are losing drive and/or pointing potential. With too little sail twist the tell tails will be sucked out of sight behind the sail You are creating unwanted drag. Ease the vang until the tell tails just reappear. In very light winds you must have almost no tension on the vang, or the leech will not be free to twist a little the sail will be 'constipated' and the boat will feel dead and unresponsive. The sail needs to twist a certain amount to allow air to flow freely off the leech, encouraging an efficient airflow across the whole sail. On a dead run or very broad reach the leech tell tails are no help. Ease the vang enough to let the mainsail head twist forward to maintain some proper airflow in light/medium winds. Very light winds Remember that you will need a small but specific amount of vang to get the top batten to gybe / tack in light winds. It is worth marking the vang system to be able to achieve this vang setting at will. b) In strong winds Beating, if you are overpowered. Forget the leach tell tails and just worry about flattening and twisting the sail (tight vang, tight outhaul, tight cunningham) as necessary to lose power. If the rig is designed to be raked the mainsail settings do not change significantly as the rig is progressively raked to reduce power. Excessive unnecessary rake is a good recipe for pointing badly. Reaching and running A sail with some twist is fast, but tends to make any Merlin less stable, particularly running. Putting more centreboard down will dampen any tendency to roll. If this is not sufficient, use extra vang to reduce twist, and/or sheet the boom closer in. It is faster to sail with a twisting sail and more centreboard down, than to keep the board raised and overtrim the sail to inhibit rolling. Raked rigs should be set more upright and with a minimum of rig tension. BOOM ANGLE (traveller/hoop etc) Beating: a) Until you are overpowered, the boom should be on or near the centreline of the boat . b) As the wind rises flatten the sail progressively with the vang cunningham and outhaul as much as possible, and extra rake if the boat is set up for it. Only if you still cannot keep the boat upright and driving, then set the boom at a greater angle to the centreline, to reduce heeling. Sailing in waves it may pay to set the boom at a slightly greater angle to the centreline than you would do for the same windstrength on flat water. OFFwind. Keeping the sheets as eased as possible with the sails still setting is fast. Oversheeting on a reach will stall the sails and ruin the effective airflow over their leeward side. PART C. TROUBLE-SHOOTING A selection of possible problems and their common causes: PROBLEM POSSIBLE CAUSE POINTS TO OBSERVE Slow upwind light winds Not enough sail twist. Is vang or mainsheet or jibsheet too tight? Check top leech telltail "Pinching" Watch luff tell tails. Sails too full Is outhaul too eased? Are fairleads too far forward? Try mast prebend Boom too close to c/line Boat heeling? Zero heel is fast Not pointing in normal conditions Too much Rake? Too much sail twist. Is vang, mainsheet or jibsheet too slack? Are fairleads too far aft? Too much mainsail twist. Is cunningham too tight?. Is vang too slack? Boom too far outboard. Set boom near centreline Boat heeling? Zero heel is fast Slow upwind in strong winds Overpowered? Not enough rake? More vang? Part-raise centreboard? Check rig tension. Try some cunningham. Ease strut/lowers a fraction "Pinching" Watch luff tell tails, depower rig to sail boat upright. Not Pointing? Are fairleads set too far back? Is the mainsail overtwisting? Boom eased out too much? Boat heeling? Zero heel is fast Slow offwind in light winds Too much rake and /or rig tension? Whole mainsail stalled (mainsheet not eased enough) Top of mainsail stalled (not enough twist) Is vang too tight? Jib overtwisting Fit barber haulers Jib stalled Watch telltails on lee side Spinnaker oversheeted Check pole height Boat heeling? Zero heel is fast Slow offwind in stronger winds Too much sail twist Is Cunningham still tight? Too much sail twist Is vang too slack? Sails stalled. Watch luff telltails on lee side. Spinnaker twitchy or oversheeted Check pole height Crew twitchy Change crew. Top batteb reluctant to tack / gybe Batten too soft or tied too tight. Or both. PART D. SPINNAKER HINTS If some of your spinnaker luff collapses before the rest, something is wrong. With the pole height correct the luff of a good spinnaker will 'break' (i.e. progressively collapse at the luff) the majority of its height at the same time, and will fly steady with the sheet considerably eased compared with a sail either set or cut incorrectly. If the spinnaker can set with its sheet more eased, then so can the jib and mainsail without suffering backwinding. Keep all the sails setting but keep them as far off the centreline as possible, and you create a rig strong on drive and acceleration, low on heeling and drag. If the spinnaker is oversheeted, then so will be the jib and mainsail, and nothing destroys boatspeed more effectively than oversheeting the sails on a reach. There is a very simple rule. If the luff is not 'breaking' evenly for most of its height, the spinnaker pole's outer end should be tilted towards whichever end of the luff is collapsing first when the sheet is eased.: If the upper luff collapses, UP should go the pole end. If the lower luff collapses, LOWER the pole end. Set your pole height to this rule on a shy reach on a maneagable day and it will be fine for all points of sailing in most conditions. Do not worry too much about the position of the inboard end of the pole on the mast, it is the height of the outer end which really matters. Some final pointers: 1. Have a slightly lower pole setting for very light airs, to keep the sail more symmetrical when the clew cannot be prevented from drooping. 2. Kevlar or Spectra sheets make a huge difference to setting the pole effectively near the forestay in stronger winds. Mark the sheet /guy at the cleat with the pole almost touching the forestay. 3. Less kicking strap and loads of cunningham will help you carry the spinnaker on a windy shy reach. Keep the JIB sheeted 'loose'. In really extreme conditions ease the strut / lowers (if deck-stepped, tension the puller wire more.) 4. Do not raise the pole end in strong wind. It does not help. 5. Many sailors worry a great deal about hoisting, lowering and gybing their spinnaker, but too little about setting up correctly for speed. Pole height is thekey. FINAL NOTE. These notes can help form a foundation from which to develope your own techniques and preferences for getting the best from your rig. Conditions will change frequently during most races. A well tuned and set up rig will cope with many of these variations automatically, particularly in stronger winds. Your alertness to sail trim will often reap significant dividends in efficiency. If you think a rig adjustment may be needed, the chances are you should already have done it! You can always change it back. © BATT SAILS 2000