leondumoulin.nl June Revision. MAINSAIL TRIM GUIDE. Your new mainsail has been designed to be easy to trim effectively.
Table of contents
- Sail Trim 101
- Sail Trim « Ian Short Sails | High Performance Racing and Durable Cruising Sails
- Stuff You've Looked At Recently
- Jib Trimming: An Illustrated Guide
The Cunningham eye or luff tension should be on quite hard to keep the draft forward in the sail and the outhaul should be tensioned quite hard to flatten the foot area completely. The traveler should be worked quite aggressively up and down through the gusts and in lighter winds to keep the boat on its feet.
I have found a lot of crews have a tendency to reef the mainsail far too late, waiting until the boat is over-pressed and the mainsail is flogging excessively, i. A reef in the main will dramatically improve windward performance with less leeway and better boat speed. The genoa or jib should be trimmed with the genoa car set well aft up to to mm aft of the optimum sheeting point with the sail tensioned in on the sheet to approximately 20mm from the spreader tip and even inside the line of the spreader on shorter footed headsails.
This will really flatten the foot area and allow the top to twist off to depower the headsail. It is important to have the backstay at maximum tension to help reduce forestay sag.
Heavy weather headsails are cut with a lot more luff hollow to allow for more forestay sag, but excessive forestay sag will slow the boat and affect pointing ability. The helmsman should feather the boat into the start of stronger gusts making sure to pull away to the optimum windward heading just before the gust passes to keep the boat on its target upwind speed.
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The mainsail is set for medium to heavy conditions. These are mast over-bend creases taht indicate the backstay is on too hard. A lot of racing boats, are using specifically designed reaching sails such as jib tops full cut, high-clewed genoa and Code 0 flat cut, minimum to mid-girth asymmetric spinnaker sails for tighter reaching legs. These sails are used before the wind angle moves aft enough to permit spinnakers to be flown, i. They are proving very successful in their designed conditions and are powered up by moving the sheeting angle forward and depowered by moving the sheeting angle well aft.
The true wind angle we are covering in this section is 38 to 95 degrees True wind Angle. It is important to trim the sails to be as powerful as possible; this is done by easing the backstay and outhaul right off and relaxing luff tension. The sails should be trimmed on the sheet so that the telltales all the way up the sail are flowing horizontally.
Moving the genoa sheeting position outboard is beneficial as this opens the slot between the mainsail and genoa. The person on the helm should be tending to sail the boat up in the lighter wind patches to keep the boat speed up and away in the gusts to make the boat accelerate, the sail trimmers should be adjusting the sails in and out to suit. To minimise weather helm the mainsail should be flattened out by bringing on the backstay and outhaul.
The leach should be twisted off easing the mainsheet. These adjustments will also help minimise excessive heeling. I would also recommend moving the genoa car aft and outboard to flatten the foot and open the upper leech area which depowers the genoa. In the heavy reaching conditions it is important to set the boat up so that it is not over- pressed and rounding up. If the mainsail is back-winding excessively move the genoa cars well aft to allow the genoa leech to twist open this will mean the upper luff tell tales will be lifting quite aggressively, but the lower luff telltales will still be flowing correctly and pull on the backstay and outhaul to maximum tension which will blade out the mainsail, this will also help tighten the forestay which will flatten and depower the genoa.
Problems can be corrected by adjustments of the jib fairlead position. A forward lead placement causes a more direct, downward pull on the leech, straightening the leech and bringing the upper sail inward. Figure 2a illustrates a sail with its lead too far aft, and the upper sail is presented to the wind at too broad an angle. The turbulence causes the upper telltale to dance forward while the middle and lower stream aft.
After moving the lead forward Figure 2b , the upper sail is brought inward, more in alignment with wind flow, and the telltale matches those lower on the sail. To determine the proper position of the jib leads, slowly turn the boat into the wind while watching the telltales.
Sail Trim 101
As the sail begins to luff, all the telltales should begin to flutter at the same time. If the top telltales lift first, there is too much tension on the foot of the sail and the lead needs to be moved forward. If the bottom telltales lift first, move the lead aft. This will work well in winds up to around 15 knots, but as wind strength increases, the lead blocks will need to be moved aft. This is a tactic used to decrease pressure in an overpowered sail, opening the sail's leech up to spill excess air out, but normally we want to maximize power by making the top and bottom uniform in the presentation to the wind.
Course changes call for more fairlead adjustments. When wind moves aft and the sheet is eased, the lead must go forward to compensate and close the upper leech. Wind more ahead calls for increased sheet tension and leads moving aft.
Sail Trim « Ian Short Sails | High Performance Racing and Durable Cruising Sails
Hoist the main as you would the jib, eliminating horizontal and vertical wrinkles with adjustments in halyard tension. Sheet tension most directly controls the sail's upper leading edge, with a lesser effect on the lower sections. Tensioning pulls the upper portion in to alleviate fluttering of the inward telltale, while easing the sheet allows the upper mainsail to "billow" more, exposing the outer side to more wind to control fluttering of that telltale. The wind higher aloft is usually stronger and more aft than wind at the surface; this is called wind shear.
Therefore, it's often necessary to trim the mainsail differently up high than at deck level, and outer telltale fluttering calls for easing of the sheet until the outer portions receive enough airflow. This is called mainsail "twist," and trimmers are said to "twist off" the upper main. When the main is trimmed properly in light to moderate breezes, the boom is often parallel to the upper batten, but with more wind or greater wind shear aloft, the top batten must be eased more. Note the similarity between jibs and mainsails in this adjustment; moving the jib lead aft is like easing the mainsheet tension.
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Both adjustments result in opening of the upper sail. The depth and position of draft in a sail are important trim considerations because they determine pointing ability, sail power, and degree of weather or lee helm. Draft depth must be decreased and moved forward as wind strength builds or we change course to point higher. This article was first published on SailNet in April of On-the-job training with some great tutors taught the author the nuances of mainsail trim.
The first time that I recall being asked to trim a mainsail was aboard a new foot PHRF racer a few years back. I was a little intimidated because my boss at the time, Ken Read, would be doing the driving. But I had read plenty of articles about mainsail trim, and so, even though I had very little onboard experience with mains, I felt up to the task.
Stuff You've Looked At Recently
The greater the acceleration, the greater the lifting force. Think of air escaping from the opening in a balloon. This exodus is not orderly. Let go of the balloon and watch it do loop-de-loops. Turbulent swirls disrupt the smooth flow over the sail, causing it to slow down abruptly and detach, or stall, from the sail.
Jib Trimming: An Illustrated Guide
And stall reduces lift. Altering the shape and the trim of the mainsail as the boat changes heading is the key to optimum sail trim. So all I had to do was to figure out how to maximize lift and minimize drag and I would be all set. So I knew how a main should look: The maximum draft shape should be located at 38 to 48 percent back from the luff.
The lower third should be flat to reduce drag under the boom. The middle third needs a bit more shape. This section promotes lift with its longer chord length the luff to leech straight-line measurement. The added area accelerates flow, thus increasing the lifting force. The top third is a bit trickier. It is designed with as much depth as it can take. The added depth increases surface area, giving the airflow a longer runway on which it can accelerate. Depth also reduces the effects of drag, by giving the airflow more time and area to generate lift before it reaches the turbulent leech.
Further, depth creates a twist. In other words, under a given sheet tension a main with more depth up high will fall off, or twist, to leeward. Seen from behind, the sail looks like a fan blade. The twist flattens the curvature, reducing the chance of separation.
And twist also combats surface friction. The air moves faster the higher it is, and a faster-moving breeze approaches the sail at an angle aft of that of a slower breeze. In order to maintain a uniform angle of attack the angle where the apparent wind direction intersects with a straight line from the leech to the luff , you need to turn off the leech.
A greater angle of attack creates more lift.
And lastly, I knew all the controls: The backstay flattens the main and moves the draft aft. The cunningham and halyard pull the draft forward, and flatten the leech.