1720 TUNING GUIDE
Tuning Set-up
BEFORE YOU STEP THE MAST
Before stepping your mast there are a number of things to do that will make your boat easier to sail and the sails easier to trim.
MARKING THE SPREADERS
Before stepping the mast put a mark on the underside of each spreader (first spreader up) 100mm in from the spreader tip. Use either coloured tape or a felt tip pen. We’ll use this mark later as a guide to trimming the large jib.
JIB TRACKS
With a high aspect ratio jib like the 1720’s, the lead position is crucial to good speed. The stock hole spacing on the tracks is simply too far apart to get the lead right in all conditions. We suggest drilling one extra hole between stock holes on the track. Also drill out the heads of the screws to increase your adjustment possibilities. It is only necessary to do this at the back half of the track, as the front half is never used.
MAINSAIL
The 1720 main has one full-length batten at the head and three long battens at the base. The batten pockets on your North mainsail are a little different to accommodate these long battens. These pockets use Velcro closures rather that the traditional elastic to keep the batten in. The amount of pressure on the pocket is important especially on the upper batten. Be sure your battens are tight enough to remove any vertical wrinkles coming off the pocket, but not so tight as to induce curve in the batten. If the sails are new just put a bit more tension for the first outing just to allow for give in the batten pocket. Be sure to check your batten pocket tension when sailing.
TUNING THE RIG
These steps will get you set up to sail the boat in moderate conditions and give you all-purpose tune. In the following section we will describe adjustments to make the boat perform at it’s best in the full range of wind and sea conditions.With the rig in the boat and the forestay in place tighten the caps and lowers by hand until firm and you cannot tighten them any more. At this point adjust the gooseneck shrouds to centre the mast at boom height. To do this use a tape measure and check the exact length of each shroud to ensure accuracy. Again at this point the gooseneck shrouds only need to be hand tight. The next step is to measure from the masthead down to the chainplates on both sides. Tighten or loosen the upper shrouds until the mast is centred from side to side. Once you have achieved your AP setting you should mark the shrouds before de-rigging to make setting up the rig faster next time. Unfortunately at present the class rules outlaw the use of calibrated bottle screws, which in our opinion is a backward step as they make setting up the rig a piece of cake! Using a Loo’s model (PT-2) Tension gauge, tighten the uppers evenly, until the uppers measure 28 on the gauge. Then tension the lowers to 23 on the gauge and this will give you approximately 55mm of pre-bend at the spreaders. The gooseneck shrouds need to be set at around 5 on the gauge, and then you will be almost ready to sail! The final step is to tension the topmast shrouds. Now we are all using the double spreader rig these can be set a little looser than before, and we recommend that with only a 1/6th of the backstay travel applied the top shrouds should be hand tight. This is a little hard to describe in words but take a little time to determine the travel of the backstay, if in doubt put on slightly more rather than less!! Hook up the backstay, install the boom and you are ready to go sailing in moderate conditions. We have found these settings, to be good starting point for most people. Note: The rig tension measurement is taken without the backstay hooked up or the boom hanging off the main halyard. The weight of the halyard or tension in the backstay can effect shroud tensions. So to be consistent, we always leave these items loose when tuning the rig.
ADVANCED RIG TUNING
Adjusting the tension of the upper and lower shrouds changes the amount that the headstay can sag and the amount of pre-bend in the mast, which directly effects the fullness of the jib. Shroud tension also effects the mast and mainsail shape by controlling fore, aft and sideways bend of the rig. In general you will want the pre-bend reduced in lighter conditions and increased in a breeze. The aim of this is to increase and decrease the amount of power available from the up-wind sail plan. From our starting set up described above we will increase and decrease the tension on the lower shrouds to change the amount of bend in the rig. All the settings below start from the base settings which we have stated above:
0-5 Knots – Take 2 turns off the caps and -1 turn on the lowers
5-10 Knots – Take 2 turns off the caps
10-15 Knots – Leave as base
15-20 Knots – Add 2 turns on caps
20-25 Knots – Add 2 turns to caps and add 1 turn to the lowers
25-30 Knots – Add 3 turns to caps and add 2 turns to the lowers
The above settings are a good guide for changing gears but do not take into account the sea state. You will therefore find you can go tighter than those suggested in flat water, but will probably want to go looser in really choppy water down the wind range.
Sail Trim
MAINSAIL
Mainsheet
Upwind use the mainsheet functions to control the overall amount of twist in the leech of the mainsail. Once the traveller is set, we trim the mainsail until the back end of the top batten is parallel with the boom. We then fine tune the mainsheet tension depending on what gear we want to go in. If we want the boat to point we can trim the mainsail harder, reducing twist and the helm will load up a little allowing us to point higher. Eventually, as we point higher, we will slowly lose speed and need to foot off again. In order to foot we need to ease the mainsail slightly to twist open the leech and ease the load on the helm, we can then drop the bow down slightly to foot and build speed without heeling the boat over and inducing helm. The mainsheet can also bend the mast and flatten the sail (especially near the top).
Traveller
The traveller controls the athwartship’s position of the boom when sailing upwind. We’ve found that it never pays to have the traveller car more than 6″ above the centreline of the boat. In general the traveller will be on or very slightly above the centreline in light air, and below, or well below in moderate to heavy air. Once you are overpowered constantly, or sailing in waves, it is generally faster to keep the traveller fully down and drive the boat a little faster through the water. The 1720, like many other one designs needs to be sailed flat upwind. In puffy conditions it is often faster to play the mainsheet when a puff hits, than to ease the traveller or feather the boat. The goal when playing the mainsheet upwind is to keep the boat flat and on an even angle of heel through all changes in wind velocity. Start judging the angle of the jib against the horizon and work to keep it constant.
Outhaul
The Outhaul controls the depth of the lower third of the mainsail. Upwind, except in very light air and choppy water, the outhaul should be tight or out to the black band. Downwind, reaching or running, let the outhaul off so that the middle of the foot is 5″ away from the centre of the boom. In heavy air you may want to keep the outhaul tight to de-power on the reaches and project more sail area. We like to keep the outhaul tight upwind to reduce the amount of drag the lower part of the sail produces. The sheeting angle of the jib is very tight on the 1720 and easing the outhaul too much upwind will reduce the size of the slot and result in poor flow between the mainsail and the jib.
Boom Vang
In moderate conditions upwind we trim the mainsheet to where we want it and then take the slack out of the boom vang. This way when we ease the mainsheet for a puff and the boom does not rise up and twist open the mainsail leech. As the wind velocity increases the vang starts to become redundant up-wind and all of the loads are taken on the mainsheet only. The real benefit of this is that when you ease the mainsheet in a strong gust the sting is taken out straight away and the boat does not heal excessively.
Cunningham
The cunningham is used to control the draft position in the main. Our mainsail is made from very low stretch Mylar that does not change shape much as the wind increases. Because of this we find we do not need to use the cunningham much except in very heavy air. Upto about 16 knots, tension the cunningham enough only to leave slight wrinkles coming horizontally off the mast. After that if you feel that the draft has moved aft slightly, use only enough tension to pull it back forward to it’s designed position.
Backstay
The backstay is probably the least used mainsail control on the 1720. Upwind we do not use the backstay until about 18-22 knots of wind. At that point after dropping the traveller, the boat will still be slightly overpowered. Tighten the backstay very lightly to bend the top of the mast and de-power the sail. After tightening the backstay, the top of the main will twist open requiring you to trim the mainsheet slightly. Conversely, if you ease the backstay the main leech will tighten slightly forcing you to ease the mainsheet. If you find the mainsail starts to flog in an uncontrolled manner at this point remove backstay tension, as this is a sign of too much backstay. If in any doubt let it off and sail with the smallest amount on. Downwind in heavy air you will want to keep some tension on the backstay to keep the mast from moving too far forward. The swept back spreaders of the 1720 rig keep the mast from moving forward and you can keep the backstay loose downwind in light to moderate airs. As good practice get a crew member to sight up the mast to check for reverse bend. If the mast is bending forwards apply backstay until it comes straight.
Genoa Trim
We start by finding the correct lead position in the moderate air. Remember if the inside top tell tail breaks first, move the lead forward until all tell tails break together. In light to medium airs we usually sheet the genoa with 2 of the standard hole spacing showing. As the wind increases we quickly recommend moving the leads to the back of the track and twisting the sail but keeping the foot tight along the deck. In flat water and as long as the mainsail is not back winding, sheet the genoa onto the mark on the spreaders. As you get progressively over powered and waves are an issue, sheet the sail on or close to the spreader tip when sighting down to leeward in the cockpit. When you reach the top end of genoa conditions, sheet at the back of the track and ease the sheet as much as is required to stop the mainsail flogging. Anything that can be done at this point to keep the leech of the mainsail working will result in better speed upwind. At the other extreme be sure to keep the sheet well eased in light air to twist open the top of the jib and keep the slot open. You will probably be sheeting 85-100mm outside the mark in less than 6 knots. The halyard tension on this sail should not be over tensioned, small wrinkles should always be showing from the hanks, in all conditions. Take care when using the winch on the halyard as it is very easy to over tighten the luff and damage the sail. Extreme care must also be taken when raising and lowering this sail and always ensure that the sheets are not cleated when hoisting and lowering otherwise the sail will tear behind the hanks.
The Asymmetric System
The first thing you need to decide before rigging the spinnaker is whether you are going to gibe the spinnaker clew between the spinnaker luff and the jib or out around the spinnaker luff. We recommend that all gibes are done inside the spinnaker luff in all conditions. Gibing inside is faster, although it can get pretty exciting when the breeze is up. Gibing outside is usually safer in heavy air. But due to the long spinnaker pole on the 1720 we think it is safer to gibe inside all round.
Setting the Spinnaker
We always set the spinnaker to leeward underneath the boom. The first step is to set the pole (bowsprit). Next we hoist the sail up to the hounds before any attempt is made to pull on the tack line. One crew member usually helps to feed out the sail from the bin. As the boat heads downwind and before the boom is all the way out, we quickly pull the tack line while the mainsheet man trims the sheet. The idea is not to pull the tack of the sail out of the boat as you approach the weather mark, but to wait until the head of the spinnaker reaches the hounds. Keeping the tack back slightly helps to reduce the chance of the sail filling too early, and sliding under the boat! This is not fast!
Gibing the Spinnaker
Gibing the 1720 spinnaker is probably the most athletic job on the boat because there is a lot of sheet to pull in. We find that it is not how fast the old sheet is eased that is important, but how fast the new one is pulled in (at least on inside gibes).
Start your turn slowly, easing the spinnaker sheet as the bow comes down. As the boat starts to lose speed, roll the boat to weather to turn the boat without using the tiller. As the boom comes over, quickly trim in the new sheet. Be careful not to trim the sheet too much, as it is easy to oversheet and slow the boat further. The outside gibe is much the same, except that easing the old sheet quickly is much more important to get the spinnaker clew out in front of the boat early.
Dropping the Spinnaker
We always try to take the spinnaker down on the port side, normally the weather side, so that we are already set up with the spinnaker on the correct side for the next set. The best way to do the weather take down is by coming into the leeward mark a little high. You can then run down right at the mark, making it easier to pull the clew around to the windward side of the boat. Drop the asymmetrical as you would a regular spinnaker by gathering the clew first, easing the tack line fully, and then finally the halyard checking the progress to ensure that the sail does not touch the water!
Trimming the Spinnaker
Trimming the 1720 spinnaker is very easy. Basically, you trim an asymmetric the same way you would a jib or genoa. Pull the sail in enough to keep 6-8″ curl in the luff. As with any other spinnaker, be careful not to over trim. Always keep the sheet moving in and out. This apparent wind moves around very fast on the 1720, so rapid trimming and easing of the sheet is important. When reaching it is important to keep the tack of the sail within 500mm of the end of the pole. This makes the luff straighter, opens the leech and increases the forward force of the spinnaker. When running or sailing deep, let the tack line off about 1.5 – 2 metres to allow the luff of the spinnaker to roll around to windward, this will allow you to sail a little lower. In certain conditions it will pay to have the tack line on the winch and trim it on and off to keep the sail working 100%.
General notes on sailing the boat
Always sail the boat as flat as possible.
Be sure not to point or pinch too much. The foils on the 1720 are quite thin and stall easily at low speeds.
Keep the crew weight forward upwind and downwind, when not on the plane.
Move crew weight aft downwind in heavy air. We mean a long way back. Usually one of the crew moves behind the helmsman to the pushpit. This keeps the bow out of the water and keeps the boats planing.
Keep the helm as neutral as possible upwind and downwind. The boat is meant to be sailed with a neutral helm. If you have a weather or lee helm, something is wrong with your trim or set up.
Caring for your sails
Your sails from North Sails One Design are constructed from the best materials on the market today. Before we made your sails, we tested many different fabrics from the best suppliers in the world.
MAINSAIL
It is not necessary to remove the battens from the main when storing it. Be sure to roll the sail up parallel to the battens to avoid putting a permanent twist in the battens. Watch the mainsail for signs of wear on the batten pockets where they cross the shrouds. Be sure to wash the sail off with fresh water when it becomes salty and make sure the sail is thoroughly dried before storage.
GENOA
Like the main, always roll the sail after sailing and do not remove the battens. Occasionally wash the sail off with fresh water. If you have been using a lot of leach line on the sail remove this before storing.
SPINNAKER
The best thing to prolong the life of your spinnaker is to always store the sail clean and dry. Although this is not always possible! When the sail gets wet in salt water (and it will) wash it off with fresh water and dry it thoroughly if leaving for a long period of time. Fold your spinnaker to store it if possible.
