Wednesday 24 July 2019

Sail Trimming Tips

This aim of this article is to provide you with a few tips to help optimise your sail trim and get the best out of your sails. As with all trim and tuning guides, this is just that, a guide. This information should not be taken as absolute. It is impossible to sail strictly by the numbers. Trim and tune are dynamic, requiring constant changes to get the most from the boat. It is more important to understand the concepts behind tuning, and the effects of the different controls so that you can learn how to shift gears. Keep an open mind and experiment in changing conditions to determine the right combination for the moment, or simply what works for your sailing style. There is no one way to make your boat go fast. The single most important thing is to recognise when you are slow and to do be prepared to do something about it.

Upwind Trim: Headsails

Most race boats will carry at least 2 headsails to cover the wind range but some boats will certainly carry 3 or 4. On modern boats with non-overlapping rigs the Code 1, Code 2 and Code 3 Jibs will all be more or less the same size. They will however differ considerably in shape and weight to accommodate different wind speeds. On a more traditional boat with overlapping headsails the differences are a little more obvious as the sails will differ in area quite considerably from one another. Within this guide I will not endeavour to provide tips for each sail, but will consider the basic tools that the trimmer has at his disposal for any headsail.

Increasing halyard tension pulls the
camber in the sail forwards
1.        Halyard: Every sail will have been designed with its position of maximum camber and entry angle placed optimally for its anticipated wind range, the boats characteristics, expected headstay sag and materials used. A sail is used across a range of conditions so it is necessary to adjust the shape of the sail to suit. Put simply, increasing halyard tension pulls the camber forwards and flattens the sail, and easing the halyard lets the draft go aft with the sail getting a little deeper.

The basic rule is to use enough halyard tension to just smooth out the wrinkles in the luff. In light airs it is better to have slightly too little tension than too much. This makes the entry finer which will help with pointing, and will also power up the back of the sail. As the breeze increases, you need to use more halyard tension. This will round up the entry which makes the steering groove wider, and will also flatten the exit of the sail, which in turn de-powers it. Care should be taken with the No.3 jib as insufficient halyard tension and/or excessive forestay sag will result in the sail being ‘too round’ which produces excess drag causing the boat to heel over. Using lots of halyard tension helps to prevent this. It is vitally important that your jib halyard is marked so that you can easily re-produce fast settings. Care should be taken not to use wrinkles on the luff or a mark on the forestay as the guide to halyard tension. Instead, the trimmers should use the camber stripes in the sail as the main point of reference. Note that as a sail ages it will typically shrink in the luff and stretch in the leech which means that the camber in the sail will gradually creep aft. This in turn will mean that more halyard tension will be required to hold the draft forwards as the sail ages.
2.       Sheet Tension: the genoa sheet is perhaps the most important headsail control and must be played constantly, easing to accelerate, trimming to point. Sheet tension will change with every change in wind speed, but the basic premise is to trim as hard as possible without slowing the boat down. Remember speed first, then point. Adjustments are not as frequent in steadier breeze, but the sheet still needs to be adjusted for changes in wave patterns or to duck other boats. Sails can be sheeted harder in flat water than they can be in lumpy seas for the same windspeed. If you are fast sheet harder, if you are slow, try easing it slightly. In light airs the genoa trimmer should be sat to leeward, and should be constantly monitoring the shape of the genoa relative to the speed of the boat. Use the spreaders and shroud base as reference points so that known fast settings can be reproduced. Again, as the windspeed increases, so will sheet tension. On boats with overlapping sails do not be afraid to have the foot of the genoa touching the shroud base, but the leech should not ever touch the spreader tips.

3.   Lead position: The base setting for the jib lead should apply roughly equal tension to the foot and the leech of the jib, i.e. an imaginary extension of the sheet through the sail would roughly bisect the luff. The standard method for determining the median sheet lead position is to luff up slowly and watch the luff of the sail. It should luff at about the same time from top to bottom. If the top breaks too early, and the bottom of the sail is strapped to the shrouds, then the lead needs to be moved forward. If the foot of the sail is very round and well off the shrouds, while the top is in close to the spreader, the lead should be moved aft. Close attention therefore needs to be paid to the leech profile of the sail as well as what is happening at the luff. If the car is too far forwards the leech will be too tight and the bottom of the sail too full; as well as being slow this will cause unnecessary backwinding. Similarly, if the car is too far aft, the foot of the sail will be tight but without sufficient leech tension.
Base lead position applies roughly equal tension to leech and foot
The lead should be moved aft as the sail is sheeted in harder and operates closer to the top of its range. In light conditions, as the sheet is eased, the lead will need to move forward. A useful rule of thumb is that if you are needing to drop the traveller to keep the boat on its feet, then move the lead aft. Similarly, if the genoa is trimmed in normally, the main has been flattened, and there is still excessive backwinding, move the lead aft. Basically, as you become over powered, move the lead aft, and do not worry if the top tell tales don’t fly properly as you open the leech up. If your jib is trimmed so that the whole sail is working, but the mainsail is flogging to keep the boat on its feet, ease the jib. Give away the top of the sail to balance the boat allowing both sails to do some luffing.

4.     Forestay Tension: In light conditions you will need more forestay sag to make the genoa fuller and this is achieved through easing the forestay if that is possible, or easing the overall rig tension if possible, or making sure that the backstay is eased, mainsail trim permitting - see below. Similarly, in heavy conditions the rig is tightened helping to prevent forestay sag. This de-powers the jib and helps pointing.
Tightening the forestay flattens and depowers the sail

Upwind Trim: The Mainsail

Mainsail trim has two primary goals. First, balancing speed versus pointing by controlling the twist or how open the leech of the mainsail is. Second, keeping the right amount of overall power, helping to maintain a constant angle of heel and the right amount of weather helm. This section will address adjustments to mainsheet, traveller, outhaul, halyard, cunningham, vang and backstay.

1.        Mainsheet: like the jib sheet, there is no one magic setting for the mainsheet. It should be adjusted continually with each change in wind speed and/or wave pattern. Basically, increasing mainsheet tension reduces twist and tightens the leech, which makes the boat point, but also slows it down. Easing the sheet induces twist, which accelerates air flow across the sail. This allows the boat to bear away and accelerate. Initially, the main should be sheeted until the aft section of the top batten is parallel to the boom. Check this by looking up the sail from underneath the boom (see picture below). This is the ‘default’ or base position and at this point the top tell tale will be on the verge of stalling but should be flying about half of the time. Once the boat is upto speed, increase sheet tension until the boat starts slowing. Remember, speed first then pointing. The art is to find the delicate balance between speed and pointing, always trying to trim as hard as possible without giving away too much speed.
Base position with aft end of top batten parallel with boom
In light air, the sail will be eased and twisted from the base position. In moderate air the sail will be sheeted hard with the top batten at least parallel. In heavy air the sail should be sheeted as hard as the angle of heel will allow. Bear in mind that in choppy seas, more twist is required to keep the boat moving, and on flat water you need harder leeches for pointing.
Above: flatter sail with more twist. Note the top batten
is falling to leeward below the line of the boom. 
More leech tension creates a more powerful sail with the top
batten being pulled above the line of the boom. Be careful
not to stall the sail in this situation

2.      Traveller: the traveller serves two functions. Firstly, it controls the booms position relative to the centreline of the boat, and secondly it helps to steer the boat by controlling the helm and angle of heel in the puffs and lulls. To position the boom, set the twist with the mainsheet and use the traveller to put the boom on the centreline for maximum power and pointing. In light air the mainsheet will be eased to promote acceleration and keep the leech open and the traveller will be well to windward to keep the boom close to the centreline without too much downward pull from the mainsheet. In moderate conditions small adjustments will be necessary to control helm balance. It is important to dump the traveller quickly when a gust hits and you begin to get over powered, but equally important to pull it back on again as soon as the heel is controlled or the gust has passed. Wait too long and you have missed the opportunity to point once the boat has accelerated. As the wind speed increases the average position of the traveller will be slightly further down the track. In over about 18 knots of breeze you may need to ease a little mainsheet as well. However, before you ease mainsheet in windy conditions you may want to have the vang pulled on hard in order to prevent giving the whole leech away. Think of the traveller as the ‘tip meter’ once the mainsheet has been set for twist. The traveller position should be monitored continually and may need to be adjusted with every change in heel or any time the mainsheet is adjusted. 

The big question is whether to dump the traveller or mainsheet in the gusts or as it gets windier. Well both will work. The first school of thought says that easing the traveller down the track in the gusts means that all leech tension is maintained and therefore the boat will continue to point. The downside to this approach is that the slot between the mainsail and genoa becomes choked, the mainsail backwinds, and the sail plan loses efficiency. The second school of thought which counters this is that instead, the mainsheet should be eased slightly in the gusts which will enable the top of the sail to twist off thus depowering the it (and keeping the boat on its feet) but because the traveller is still well up the slot remains open and the tension in the lower leech will keep the boat pointing anyway. The trick is to work out what works best for you and your boat. One rule of thumb though is that if you feel you have to ease the traveller, the mainsail should be fully flattened and depowered via the other controls (see below) before you get to that point in order to minimise backwinding. If you end up in a situation where the whole sail is ragging wildly then something is wrong; there is no reason why the sail should be flogging with correct trim and set-up! For more subtle changes in wind speed it may be better to use small adjustments to the traveller to fine tune the helm. In the big gusts dumping the mainsheet will get the boat back on its feet more quickly but be sure to get it back on as soon as possible.
3.       Vang: the vang is primarily an offwind control. It takes over the job of pulling down and providing leech tension when the boom is eased out and the mainsheet is no longer controlling the twist. However, upwind, certainly on smaller boats the vang can be used to help out the mainsheet with the job of pulling down the boom and maintaining leech tension. If the vang is hard on, the mainsheet can be eased in big gusts without giving up too much of the leech . In light air make sure the vang is off using only enough tension to stop the boom from bouncing. In heavy air it will be necessary to ease the vang at the weather mark to assist with bearing away. Easing the mainsheet may not be enough.

4.       Luff tension (halyard and cunningham): halyard and cunningham both tension the luff. Initial luff tension should be just enough to smooth out the wrinkles in the front of the sail. Leave a few wrinkles in the bottom third of the sail in light to moderate air. As the breeze increases more luff tension is required to prevent the draft in the sail from moving aft. Use the halyard first, and when the sail is at the black band use the cunningham. Do not under estimate the usefulness of the cunningham, it is one of the primary sail controls that many people choose to ignore. As soon as the boat is overpowered start pulling the cunningham on hard upwind. It is easier to adjust and fine tune the cunningham when sailing than the halyard. As with the headsails, as the sail ages the camber will creep aft so more luff tension will be required to keep the draft in the correct place. Use the camber stripes as a guide.

5.       Outhaul: the outhaul controls the depth in the lower third of the mainsail. If you need more helm and feel, ease the outhaul. Power in the bottom of the main will increase weather helm. In very light airs (less than 5 knots) the outhaul needs to be pulled out fairly firmly in order to prevent flow separation in the lower part of the mainsail. If the sail is too full in these very light airs it will stall. In 5-12 knots the outhaul can be eased slightly to increase power. Once the boat is fully powered with all the crew hiking (normally about 10-12 knots of wind) the outhaul should be maxed out. The outhaul should be eased  when running but be careful not to overdo it, when trying to run deep you may find that having the additional maximum projected area associated with a slightly soft foot is faster than having a really deep sail, I prefer to ease slightly more than is sufficient to remove any crease across the foot from its upwind setting. The outhaul should be eased for power when reaching (unless of course you are over powered!). Make sure that you have the outhaul calibrated so that you can repeat known fast settings (make sure all sail controls are calibrated for the same reason!)

6.       Backstay: On a boat with a fractional rig increasing the backstay tension does two things. Firstly, as the mast bends the upper two thirds of the mainsail flattens out and the leech opens up, thus de-powering the sail. Secondly, the headstay gets tighter (providing you have set up the pre-bend correctly to prevent over-bending), which prevents headstay sag, which in turn prevents the jib from getting too full as the breeze increases. On a masthead rigged boat, increasing the backstay tension is unlikely to bend the mast much but will have a bigger effect on the forestay. 

Broadly speaking as the breeze increases you will need more and more backstay. However, even in very light airs you may need to use a little backstay in order to help the mainsail leech to stay open. Since adjusting the backstay has a large and immediate effect on mainsail leech tension, main sheet tension needs to be adjusted at the same time. Bending the mast opens the leech, so you will need to add mainsheet as you add backstay, and ease mainsheet as you let the backstay off. You will also need to adjust the traveller accordingly.

Pre-bend and mainsail shape

The 'pre-bend' in the mast, or initial bend without backstay needs to be in harmony with the luff curve that has been built into the mainsail. If the mainsail flattens out too quickly (as characterised by overbend wrinkles running diagonally from clew to mid-mast before the backstay is maxed out), then you need tighter lowers and/or a shorter headstay to reduce bend and make the mainsail fuller. In heavy air you should be able to pull the backstay all the way on just before the overbend wrinkles appear.

If the mainsail is too full for the amount of backstay being used, as characterised by excessive backwinding, or a sail which is ‘knuckled’ and excessively round at the front, less lower tension and/or a longer headstay is necessary. Once the mast has been set with the correct forestay length and shroud tensions for medium air, these should be regarded as ‘base’ settings. In very light air decrease the tension on the lowers and add headstay length to induce additional pre-bend. Extra pre-bend and softer rig tension will also increase headstay sag creating more power in the genoa, which will also make it easier for the helmsman to ‘feel’ the boat and stay in the groove.

The uppers (cap shrouds) should not generally need to be adjusted much providing you have an adjustable forestay. The upper diagonals (D2’s) again should not need to be adjusted, but bear in mind that these also act as a control for mast bend. If the sail is too full in the upper sections, they may be too tight, and vice versa.

As a general guideline, in light airs ease the overall rig tension on the forestay and/or decrease the tension on the lowers to induce additional pre-bend. As the breeze builds, increase the overall rig tension to prevent the mast from overbending as the backstay is pulled on. You should aim to create a tuning grid similar to the example below.

0-7 knots
8-15 knots
16-22 knots
23+ knots
Lower Tension
Ease 1 turn
Tighten 2 turns
Forestay Tension
Ease 5-8 turns
Tighten 5 turns
Tighten 8 turns from base

Downwind Trim

The key to running effectively is to project as much area to windward as possible away from the mainsail, thus facilitating sailing deep. Do not get pre-occupied with having the clews at the same height as depicted by most sailing guides. You should start by altering the pole height so that the luff of the sail isn’t breaking too high or too low. You should then set the leech accordingly by using the tweaker lines. Pulling the tweakers on will stabilise the spinnaker when it is windy but don’t overdo it or the sail will stall. Use the centre seam as a guide to trim, which should be approximately perpendicular to the horizon. If it feels right it probably is right. The main thing when sailing downwind is to make sure the spinnaker is pressured up all the time. The trimmer and helmsman should be talking to each other continually so that the helmsman can get the boat really low when he has pressure and he doesn’t sail too high when he needs more pressure. Easing the vang and twisting the mainsail will also help you get deep, but at the same time it will make the boat more unstable and less forgiving. Be prepared to adjust the vang continually downwind and sail where you are comfortable. Sailing downwind is at least as tactical as sailing upwind with huge gains to be made by sailing at the right angles on the right shifts. If you tack on shifts going upwind you should gybe on them going downwind.

The crew should be well forward in light air, gradually moving aft and to weather as the breeze builds. The boat should ideally be heeled slightly to weather when going downwind which helps to project the spinnaker and helps the boat to drive off in the puffs. Weight should be shifted to stabilise the boat and promote surfing in heavy air. When it is breezy all the crew should be well aft, with one person being allocated as ‘vang man’ to de-power and power up the main as necessary.

Miscellaneous Tips

1.       Crew weight upwind: sail with a constant angle of heel, and with as little weather helm as you can stand. Generally this will mean sailing as flat as possible. In light air the weight should be to leeward and forward to induce feel and helm. In less than 5 knots of breeze it pays to put a couple of crew members down below particularly in sloppy conditions when it will help prevent pitching. Once the boat is powered up all the crew should be hiking hard and be bunched together around the maximum beam. Again keeping the crew weight together helps to reduce pitching.

2.       When the boat starts getting overpowered don’t fight the helm. Instead, ‘feather’ the boat slightly by sailing ‘inside’ the jib tell tales allowing the windward ones to lift slightly to keep the boat on its feet. Try to focus on steering to a consistent angle of heel. In other words don’t get pre-occupied with keeping the tell tales on either side of the sail streaming together.

3.       Don’t be afraid to pull control lines really hard! One of the most common mistakes that we see is things like the backstay not being pulled on anything like hard enough to depower the main or the mainsheet not being pulled on hard enough to get the boat to point!

4.       Remove all unnecessary items of kit from the boat. Encourage the crew to bring only what they are going to wear. You don’t need to have a pair of boots and a pair of shoes on the boat for example. Stow any spare kit, fenders etc over the keel.

5.       Make sure the bottom is clean and smooth. If the boat is anti-fouled, this should be rubbed flat with increasingly fine wet and dry paper. Do not under estimate how detrimental even a little bit of slime or weed can be to boatspeed. Being conservative we might say that having a dirty bottom will slow you down by 0.2 of a knot. This doesn’t sound much but it equates to 400 yards an hour. In a two hour race this is nearly half a mile!

6.       Make sure that all sail controls are visibly calibrated so that you can repeat known fast settings. This includes halyards and sheets.

7.       Similarly, put marks on the spinnaker pole controls so that you can pre-set it accurately before hoisting.

8.       Put a cover over the jib halyard at the point where it goes through the jammer. Maintaining halyard tension is vital when it is windy and most halyards will gradually slip as you progress upwind. Alternatively, keep the genoa halyard on the winch until you approach the windward mark.

9.       Keep an open mind and do not be afraid to experiment. Perhaps the most important point to recognise is when you are slow, and then to do something about it!

10.    Have fun!