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Spinnaker Trim

January 6th, 2011

Our good friends at Elliott/Pattison Sailmakers put together the following primer on downwind sail trim:

Spinnaker trim really falls into two categories; sails flown on a pole and sails flown on a fixed sprit. There are also a very few boats that fly asymmetrics on an articulating sprit but in general those articulate through a small enough range that flying them is nearly the same as flying a sail on a fixed sprit. However what you are trying to accomplish is the same in all cases. For that reason this article will focus mainly on trimming spinnakers flown on a standard spinnaker pole with some ideas on how to incorporate the same ideas for sprit sails.

There are four main controls you use to obtain the shape you want; pole position vertically, pole position horizontally, sheet tension, and sheet lead position. Basic wisdom has always been to fly the spinnaker pole pulled aft so that it is perpendicular to the wind, fly it high enough so both clews are level (on symmetric sails), then ease the sheet out until the luff of the sail just starts to curl over. While this will get you close it will also leave you lagging behind the good trimmers that take full advantage of all the controls at their disposal.

For pole position fore and aft, once the apparent wind is aft of 90 degrees, the pole should be pulled back just far enough that when the sail is sheeted so that the luff is just starting to curl the sail maintains an even shape from the middle down to the foot. If the pole is too far aft the trimmer will have to sheet the sail in tighter to keep it from breaking and you will see the foot of the sail is stretched out straighter than the middle of the sail is. If the pole is too far forward when the sheet is eased until the luff just starts to curl you will see the foot of the sail is much deeper than the sail is in the middle. The other thing to look for is that the luff goes straight up nearly vertically from the end of the pole to the middle of the luff but this doesn’t work for asymmetric runners on a sprit. These sails are usually designed with a lot of luff round so that as the sheet is eased the sail will rotate well out to weather of the end of the sprit and let you sail deeper.

Setting the pole so that both clews on a symmetrical spinnaker are flying at the same height is a good starting point but the more important point is to get the sail to fly square so that it takes the shape it was designed with. I like to look at the horizontal seam where the head is sewn on and the vertical seam down the center of the sail. The pole height should be adjusted so that the head seam is level and the center seam goes straight up and down; they should be at 90 degrees to each other. This technique is very important when sailing on a boat that uses asymmetric spinnakers on a standard pole since the tack and clew will never be at the same height. It also works fine and well for a properly shaped spinnaker flying with the wind aft of 90 degrees, but that is not always what you have. By changing the pole height you can also change the location on the luff where the sail breaks first, you can pull the draft further forward which also opens the leech, and you can change the amount of horizontal camber. You want the sail to break first on the shoulder, just above the head seam where the luff profile has the most curve. If the pole is too high the upper leech will twist open and break well before the rest of the sail; if the pole is too low the upper luff will be stretched too tight and will break later than the lower luff.

What about on reaches you might ask. Well since the pole height determines how tight the luff is stretched it acts something like the halyard on your headsail. As your lower the pole and tighten the luff it pulls the draft forward in the sail and also opens the leech. This is an advantage if you are sailing on a leg that is a tight reach because the open leech lets the air exhaust without closing off the slot between the main and the spinnaker as much which will give you better speed. However if you are sailing on a reach that is very tight, where you can barely hold the spinnaker you need to remember you high school math and the Gauss-Bonnet Theorem. It says that the total amount of curvature in a surface remains constant. If you increase curvature of a surface (your spinnaker) in one direction curvature in other directions has to decrease. So sailing down a reaching leg you start out with pole slightly lower to open the leech and go faster but as you approach the mark you find the leg is getting tighter and tighter and you need to keep the spinnaker up because the next leg is also spinnaker leg. By raising the pole up in this condition you increase the vertical camber in the sail which decreases the horizontal camber which will let you sheet the sail tighter and point slightly higher. You will also go a little slower so this technique should only be used for short distances. The rest of the time it is better to sail slightly lower and keep the spinnaker working at maximum efficiency for a little longer then the switch to you headsail and come back up for the remainder of the leg.

In positioning the spinnaker sheet lead block there are two things to consider. First, the further aft you have the lead the wider the sheeting angle becomes, which helps keep the spinnaker spread as wide as possible when running; and second, the correct lead angle for reaching. It is best to sail the boat on a tight reach with the apparent wind just forward of the beam and check to see how the lead is. In this condition you adjust the lead much the same as you would for a genoa. When the sail is sheeted in tight to the point where the foot is just pulled out tight the leech curve should follow the twist in the mainsail. If the lead is too far forward by the time the foot is in tight the sheet will be pulling down too much on the leech which closes off the slot between the main and spinnaker. If the lead is too far aft the leech will be twisted too open and you lose power from the top of the sail. If this position ends up being near the transom then you can get by with just the single lead; however in most cases you will find that you want to sheet the spinnaker quite a bit further forward for tight reaching. The simplest way to accomplish this is by using tweakers, basically a block that the spinnaker sheet runs through before it gets to the sheet lead block. The tweaker block is attached to a line that runs down through another block fixed to the rail about half way between the transom and the shrouds, and then to a cleat. By pulling the tweaker block down you effectively move the lead position forward. Tweakers also give you the ability to move the lead aft while reaching if you are getting overpowered (just like moving your jib lead aft to depower) and when running in heavy air conditions you can move the lead well forward which chokes the spinnaker down and helps prevent oscillations.

Rigging and Gybing With an Asymmetric

September 7th, 2010

Sailing with asymmetric spinnakers on sprit boats has become common in the last 10 years but there is a growing trend of using asymmetrics on conventional boats with standard spinnaker poles. While these sails are very efficient they do require somewhat different rigging, and gybing them is quite different.

First let’s look at the different rigging that is required. The biggest differences are that you need a tack line instead of a foreguy on the pole, two afterguys that both go to the tack, and two spinnaker sheets that both attach to the clew. The tack line needs to go through a block right at the headstay or with an oversize pole at the point that is the same distance from the mast as your spinnaker pole length. On smaller boats the tack line attaches directly to the tack of the asymmetric using a snap shackle with a large bale. The two afterguys are snapped on to the bale of the tack shackle. Larger boats often use a large stainless steel ring with bars welded across it in an “X” pattern. The tack line attaches to the bottom section, there are two snap shackles in the top section to attach to the tack of the sail so you can do peels, and the afterguys are attached to the two side sections. Spinnaker sheets should tied to the clew rather than attached with snap shackles; during gybes there is an increased possibility of the shackles coming open as the sail is pulled across the headstay or around the luff, and there is also a  much greater possibility of the shackles ripping the sail as they are dragged across it. A “Y” sheet is widely used and consists of two sheets connected with a single short tail that is tied to the sail with a bowline. This reduces the drag during the gybe.

Sailing with an asymmetric on a pole is no different than sailing with a symmetric. You still pull the pole back the same amount and sail the same angles as you do with your symmetric, the sails are just slightly more efficient when sailing deep because they have longer luffs and shorter leeches which gets more sail area out on the weather side of the boat where it does the most good. The downwind asymmetrics, a Code 2A or Code 4A, will generally be maximum size and have a mid-girth that is the maximum for your rating. The shoulders will be just as big as a symmetric. Sailing with the apparent wind forward of the beam, either sailing vmg downwind angles in light air or because a set course requires it, the asymmetrics are noticeably better because of their asymmetric cross-sectional shape. These sails will be built with a mid-girth that is shorter than the foot, be flatter, and have much straighter leech sections. This allows them to be sheeted in tighter without forcing nearly as much wind into the back side of the main and be more open leeched so the power is utilized to make you go forward faster rather than heeling over more.

The major difference in sailing in sailing the asymmetric with a conventional pole is in gybing them. Since you are flying the sail on a spinnaker pole instead of a sprit the pole has to be gybed the same as with a symmetrical. While this is taking place the asymmetric has to be tacked to the bow. The first step is to “Transfer” the tack. This is done by easing the afterguy forward while the tack line is taken up to pull the tack down to the bow. If you are sailing in light or medium air, any time the apparent wind angle is forward of about 135 degrees, you can maintain your sailing angle during this operation. In heavier air when you are sailing deeper you may have to head up some to get to an angle where the sail with still fly when the tack is transferred to the bow.

There are two types of asymmetric gybes, the “Inside Gybe” and the “Outside Gybe”. On boats under 45’ long you can usually do an inside gybe in up to 12 or 15 knots of wind. In over that, or in bigger boats, you will usually set up for an outside gybe. In an inside gybe the lazy spinnaker sheet is led around the headstay but inside of the spinnaker, while in an outside gybe the lazy sheet is led around outside of everything. An inside gybe is faster but an outside gybe is safer, especially in heavy air. In either case you start the same, with the “Transfer”. In an inside gybe you bear away slightly while the transfer is made, making sure to stay high enough that the sail stays full and drawing once the transfer is completed. The old sheet is eased as far as possible as you turn down without letting the sail collapse. As you reach this point the new sheet is hauled in pulling the clew around the forestay and the old sheet is let completely go. DO NOT turn the boat any further downwind until you see the clew is pulled well around the headstay and almost the entire leech is visible on the weather side. At this point you can steer down quickly through the gybe and bring the boat back up to the same apparent wind angle on the new gybe. The crew continues to sheet the sail in on the new side as you steer through the gybe and as you come up to course the sail will fill quickly and pop the rest of the sail around the headstay. Beware…if you turn the boat down too far or too quickly before the clew is pulled well around the headstay you risk getting a wrap in the sail which can take a long time to work back out. As soon as the transfer to the bow is completed both afterguys will be completely loose. This makes it very easy for the bowman to gybe the pole as you are steering through the gybe. You can do either an end-for-end or a dip pole gybe depending on the size of your boat and how you normally do it. By the time you steer though the gybe and the sail fills the bowman should have the old guy out of the pole and the new guy in the pole on the new side. He shouts “made” and the tack line is eased off as the new afterguy is tensioned and the pole brought aft to its proper angle.

In an outside gybe as the transfer is being done you start to turn the boat downwind and the sheet is eased to keep the sail full as long as possible. As you reach the angle where the sail will no longer stay full slow down your turn as the old sheet is released to give the sail a chance to blow out away from the boat. As you reach dead downwind start hauling in the new sheet as fast as possible to drag the clew around the outside of the luff of the sail. Here speed is everything; having several people near the shrouds hauling hand over hand on the new sheet can really help if you don’t have a coffee grinder with two strong guys turning the handles. Once you pass dead downwind turn the boat up faster to reach the angle where the sail will fill. Turning a little faster and a little further than needed will help the sail pop full and get you accelerated back up to your target speed. The pole is gybed from side to side during the gybe just the same as in an inside gybe. As you come out of the gybe the pole is topped back up and the tack line is eased off as the afterguy is brought aft to its proper position.

If you haven’t sailed on a boat with an asymmetric on a pole this all may sound a little complex; but it really isn’t, it’s just different. With a little practice you crew will soon be will be able to gybe the boat just as efficiently as they did before.

This article was written by our frineds at Elliott/Pattison Sailmakers, please keep them in mind if you are ever in the market for sails.

Tame Your Mainsail

May 27th, 2010

On most boats you have five controls to properly shape and control your mainsail; the mainsheet, traveler, outhaul, cunningham, and mast bend. For this article we are looking at a typical masthead rig with overlapping headsails. In making trimming the main you need to be well aware of what effect changes in trim will have on performance. A flatter sail will cause less heeling and have less drag which means more speed in conditions where you are over powered, making the sail fuller will produce more power when need. A tighter leech will improve pointing (up to the point where the sail is stalled) while a more open leech will improve acceleration and speed. A fuller sail will inherently be tighter leeched than a flat sail which will help pointing.

In medium air, usually 7 to 10 knots of wind where you aren’t overpowered, the sail should take its natural shape without much adjustment. This condition is what a typical mainsail should be designed and cut for. You want to use a combination of mainsheet tension and traveler position so that the boom is right on centerline and the top of the sail is twisted just enough so that the back half of the top batten is pointing straight aft, parallel to the centerline of the boat. The traveler will have to be pulled well to weather of the centerline to achieve this. The tell tale on the top batten will be streaming back most of the time but the leech should be tight enough so that the tell tale does stall out now and then. The cunningham should be tensioned just enough to remove wrinkles along the luff and the outhaul so be set so the center of the foot is 2” to 4” away from the boom, a little more if the sea conditions are bumpy.

As the wind increases and you start to have more power than you can use flatten the main a little bit. Tighten the outhaul so the foot is pulled up close to the boom and tighten the cunningham a little more if needed to take the wrinkles out along the luff. If you have a bendy rig you should tighten the backstay to increase mast bend and flatten the sail. As you do this the leech will become more open so you will need to tighten the mainsheet enough to keep the leech tight. In this condition the top tell tale should be streaming back most all the time and you want the leech as tight as you can get it before the top tell tale starts to stall. As the wind increases you will have to starting to let the traveler down an inch or two at a time to keep from being over powered.

By the time wind gets over 12 knots you want to get the main even flatter. Pull the outhaul all the way tight and bend the mast to flatten the sail even more. If you are consistently overpowered ease the mainsheet an inch or two to let the top twist open a little more. Generally I let it twist just enough so that I’m not over powered in the average wind and then play the traveler up and down in the puffs. Pull the cunningham tight to keep the draft in the sail forward and the leech open. The top tale should be streaming aft all the time.

In the 5 to 7 knot range you want the main a little fuller to produce more lift in the under powered conditions. Ease the outhaul off so the foot is 6” to 8” away from the boom and ease the backstay to reduce mast bend. This will also make the headstay looser which will help the genoa shape in light air, making it fuller and the entry rounder. Let the traveler down a few inches so that the boom is a little below the centerline to increase speed. In these conditions you need to point slightly lower to develop speed and increase your apparent wind. Ease the cunningham so that you have a few wrinkles along the luff. You want the sail as soft as possible so that it responds to very slight changes in wind pressure. The tell tale on the top batten will be stalled 50 to 60% of the time.

In very light conditions, under 5 knots, you actually want the mainsail to be a little flatter. Too much camber and the flow in light air won’t stay attached. Pull the outhaul out just snug so the foot is up close to the boom and put on enough backstay to slightly bend the mast. This will flatten the sail and open the leech which both help to keep good flow over the sail. The cunningham should be completely loose so you have some wrinkles along the luff.

Below is a quick reference summary.

Boom position

Light air – boom 4” – 6”  down from center
Medium air – boom on centerline
Heavy air – boom down far enough to keep flat


Medium air – 7-10 knots, no tweaking, shape should be what was built into the sail, -Including designed pre-bend. Foot should have some shape, tighten the outhaul so the center of the foot is 2” to 4” away from the boom. Sheet tight enough so that top batten is PARALLEL to centerline. Top Tell tale should be stalled some of the time
Light air – 5-7 knots, main should be slightly fuller, less mast bend, ease foot so that it is 6”-8” deep. Sail with a little more twist, top tell tale will be stalled most of the time.

Very light air – 0-4 knots. Bend mast a little more than designed bend amount to open upper leech, tighten outhaul a little

Med-Heavy – 10-13 (or where you are getting overpowered) Tighten outhaul so foot is starting to wrinkle, bend mast a little more, tighten cunningham enough to take out luff wrinkles. Sheet so that top batten is parallel, top tell tale should be flying all the time.

Overpowered – Bend mast to flatten sail as much as possible without over-bend wrinkles. Pull outhaul tight, enough cunningham to remove wrinkles, drop traveler down 3 or 4”. Sheet so that top batten is slightly twisted open. Drop traveler as needed in puffs.

This article was provided from our good friends at Elliott/Pattison Sailmakers! Check them out!