Viper 640 Tuning Guide For any question you may have on tuning your Viper 640 for speed, contact our experts: Ched Proctor 203-877-7627 ched.proctor@northsails.com Zeke Horowitz 203-783-4241 zeke.horowitz@northsails.com Alex Camet 619-226-1415 alex.camet@northsails.com onedesign.com Follow North Sails on...
MAST TUNING Tuning Guide for the Carbon Mast Viper 640 Tuning Guide SET SPREADER ANGLE Check spreader angle by placing a straight edge or string behind the shrouds on top of the spreaders. Measure from the middle to the back of the sail track. We prefer to have this less than 310 mm (12 ¼ ). Ideally set it at 290 mm (11 3/8 ). MEASURE YOUR HEADSTAY Set your headstay to maximum length. From the lower side of the T fitting to the top of the pin this measurement is 7588 mm (24 10 ¾ ). MAST STEP POSITION Check which hole in the step to place the aft pin by measuring from the intersection of the rudder pylon and cockpit floor forward to the step. To the aft side of the mast this measurement should be 3710 mm (12 2 1/16 ) for the new inset style of transom or 3730 mm (12 2 ¾ ) for the old style of transom. This is often the aftermost hole in the step. MAST PARTNERS In order to best tune your Viper, it is necessary to restrict the forward mast movement in the partners. You can do this with the line and cleat that comes with the boat. We recommend using mast blocks in front of the mast for setting up for over 8 knots in order to solidly control mast bend. This provides greater headstay tension to keep the jib flat and twisted as the breeze increases. The aft block which fits against the front of the mast needs to be filed away to accommodate the angle from the rake of the mast. It s best if it fits the curve of the mast also. Properly done this keeps the blocks from climbing up. With the mast set in the recommended step position above, 3 of blocks will be required between the forward face of the mast and the front of the mast partner. For lowest wind range (0-6) remove 1 of blocking and use the line to pull the mast forward to induce pre bend and slack in the headstay. For the top setting you may need to add a block to maintain the pre-bend at 3 with the increased rig tension. On your boat a different amount of blocking may be required. See the pre bend measurements in the Uppers section below. Use a line to hold the mast forward against the blocks and keep the blocks from climbing up. This is absolutely necessary to prevent the mast from inverting when sailing downwind in heavy air. 1
UPPER SHROUD TENSION Put sufficient tension on the upper shrouds with the lowers completely slack to register 10-15 on the PT1 gauge. Check side to side using the jib halyard to center the mast by measuring to the rail on each side of the boat. Check pre bend by pulling the main halyard down to the goose neck against the back of the mast. Judge distance between the halyard and the back of the sail track at the max distance. This is usually 1-2 above the spreaders. You could use a bend checker pulled up on the spinnaker halyard. Picture example shows how it works. The yellow line is the main halyard pulled straight. For a base setting you would like to attain 1 ½ of pre bend and headstay 10 on the PT1 Loos gauge. This is a good base setting for 6 to 11 knots. How much and how soon you need to increase rig tension to control headstay sag is dependent largely on crew weight and to some degree on sailing style and wave conditions. If you have more bend add blocks in the partners to attain this pre-bend settings. If the spreaders are further aft you may need use a lot of force to put the blocks in place. The number of turns will likely vary from boat to boat: Wind (TWS) Uppers PT1 # Number of Turns Pre-Bend Measurement Headstay PT1 # 0-7 24-1 1 1/2 Slack 6-11 26 0 2 1/2 10 10-15 29 +2 2 1/2 15-19 31 +4 3 17 19+ 37 +6 3 29 Spreader Aft Upper settings require more precise settings: Wind (TWS) Uppers PT1 # Number of Turns Pre Bend Measurement 0-6 23-1 2 1/4 6-8 24 0 2.5 8-11 26 +2 2 7/8 11-15 29 +4 3.5 15-20 31 +8 4 1/8 18-25 33 +10 4 1/2 2
LOWER SHROUDS TENSION The tension needs to be adjusted precisely under load on the water. For this reason we recommend putting turnbuckles on the lowers. In less than 8 knots the lower shrouds should be set to be slack when sailing. Above 8 knots the tension on the lower shrouds becomes critical to control fore and aft mast bend, side band and to some degree the headstay tension. The tension setting in the 15-19 Knot range is barely sufficient to register 5 on the Loos gauge (model PT1). Only 1 more turn should be sufficient tension for stronger wind. Note: It is critical to not over tension the lower shrouds in heavy air. If the lower shrouds are too tight, it could contribute to inverting the mast while sailing downwind and causing breakage. Wind (TWS) Numbers of turns from base Lowers PT1 # 0-7 -4 No Reading 6-11 0 No Reading 10-15 +5 No Reading 15-19 +5 5 19+ +3 5 At base setting lower turnbuckle can be pulled up parallel to upper turnbuckle. 3
SAIL TRIM JIB LEAD POSITION Your North jib is marked with a trim line near the clew drawn from the clew grommet toward the body of the sail. Your lead should be positioned so that the sheet is a direct extension of this trim line. In stronger breeze move it aft a hole or two, or move the sail lower to the deck by using a shorter shackle at the tack. Generally the jib lead should be set more forward in light air to allow the foot to have 6 of round in it. This will have 3 or 4 holes showing in front of the jib lead. As soon as the breeze is strong enough to justify hiking, the lead should come aft as much to flatten the foot nearly to a straight line when the leech is properly trimmed. JIB SHEET TENSION Your North jib has a leech telltale ¾ of the way up he leech. This telltale can be observed by the jib trimmer from the leeward side in light air. In any hiking breeze it can be observed through the luff window in the main. This is to use in judging sheet tension. In most conditions trim the jib in until this telltale no longer streams aft, then ease it out until it just streams aft. Generally the middle batten in the jib will point straight aft when it is properly trimmed. The top jib batten is full length. In light air removing this batten helps the jib to be more powerful. As soon as the breeze is over 8 knots it is important to have the full length batten in. This helps the leech to stay open while trimming the sail hard. MAINSAIL OUTHAUL Easing the outhaul in light air powers up the main. Judge the outhaul tension at the mid point of the boom. Look at the distance between the side of the boom and the foot of the sail. In rough water light air conditions easing the outhaul to open the foot as much as 10-12 can be fast. In smoother water generally keep it tighter. As soon as there is enough wind to hike, tighten so the sail lays against the side of the boom. MAINSHEET TENSION In light and moderate conditions when heeling can be controlled with hiking, the aft end of the upper battens (on either side of the Viper insignia) should be parallel to the boom. This may require quite a lot of sheet tension. In stronger breeze applying vang and a couple of inches of sheet ease will allow you to keep the jib pressed, and the bow down with the boat moving forward. Pointing isn t the name of the game here. When the wind builds more, you may need to ease the jib to keep from healing too much. 4
GNAV (Reckik in Britain, or vang) Under 12 knots make sure the gnav isn t applying any downward pressure on the boom. This applies for both upwind and downwind. As the wind becomes stronger, apply progressively more tension to keep the boom down as the mainsheet is eased in the puffs. The Gnav bends the mast to flatten the main and tensions the headstay as long as the lowers are properly adjusted and the mast is firmly blocked aft at the deck. VIPER 540 TARGETS TWS Upwind Tack Downwind AWA Jibe Sheet 6 4.5 90 4.4 90 90 135 8 5.3 85 5 110 70 145 10 5.6 80 5.8 125 60 150 12 5.8 78 6.2 130 40 160 14 5.9 78 9 85 100 130 16 6 79 10.5 90 90 135 18 6.1 80 12 85 85 138 20 6.2 82 14 80 80 140 CONTACT NORTH If you would like to discuss setting up your sails contact the North Viper 640 experts listed on the cover of this guide or visit onedesign.com for the latest news in the Viper 640 developments. Good Sailing! 5
TENSION GAUGE CONVERSION CHART Over the past years Loos Co. has introduced it s new style PT-1, 2 and 3 professional tension gauges to the market. Since many of us are replacing our older model A and B gauges with these new models we are posting the following conversion chart for your convenience. Model A Model PT-1 3/32 1/8 5/32 5 6 10 9 15 12 14 20 16 16 25 20 19 28 23 21 30 22 35 27 25 38 30 28 40 33 30 42 33 44 36 45 38 46 39 47 40 Model B Model PT-2 PT-3 3/16 7/32 1/4 9/32 10 11 15 13 18 15 20 16 18 22 18 20 24 19 22 26 21 24 28 23 25 30 25 27 25 32 27 29 27 34 29 31 29 33 31 36 33 6 37 36 7 37 9 10 11 12 14 16 18 20 25 6