Sail Trim

This guide is based on an article by Ian Short that was first published in Australian YACHTING, May/June 2009

It’s a fallacy that only racers need to sail quickly. If you’ve ever been caught out in a gale just an hour from what would have been a safe haven – but is now a dangerous river bar – then you’ll understand that cruisers need to know how to extract the maximum speed from their boats as well. Sailing quickly isn’t just about winning races, it can be the difference between an uncomfortable and potentially dangerous night at sea and sleeping soundly, safely tied up at a dock.

In this article I’m going to explain some of the sail trim and rig adjustment tips that I’ve learned that can help you go faster on upwind and on a reach. I have purposefully left downwind sail trim out of this article as it’s a reasonably involved topic that I’ll address separately.

To ensure that these tips can be applied by the broadest possible audience, I’ve omitted some of the finer adjustments that you might find on specialised racing rigs, so just about any boat should be able to use these tips to pick up extra speed.


As a sail maker I go sailing on a lot of one-design boats. When people ask me why a particular boat goes slower or faster than its competitors the answer often comes down to who is paying constant attention to sail trim. The continuous trimming, of your sails to power them up in lighter winds and to reduce power in stronger winds can result in significant performance gains. With that in mind, here are some trimming tips I have found to be quite successful.

Upwind – light conditions
(2 to 10 knots true wind speed)

In light wind conditions it is important to set your sails up for maximum power.

The backstay should be eased right off. This affects the rig in two significant ways:firstly, it allows the mast to straighten up fore and aft, which reduces pre-bend. This makes the mainsail a fuller and more powerful shape, and secondly, it eases tension on the forestay, this allows the forestay to sag off more which induces more fullness into the headsail.

The luff tension on both sails should be eased so that they are quite relaxed, this allows the draft position (maximum fullness fore and aft) to set up in the designed position which is normally around 35% on the headsail and 40% on the main, depending on the type of the boat. Too much halyard tension in lighter winds will move the draft position in both sails too far forward which can considerably reduce your pointing ability.

While we’re on the topic of adjusting the luff tension, it’s worth pointing out that mainsail luff tension can be controlled by easing or raising the halyard, but the far easier way is to rig the Cunningham. This is a common device on race boats that all cruising boats would benefit from using.

This is good light weather trim. There is sag in the forestay to give the headsail a full, powerful shape.

2windward_LIGHT_2lowresThe mainsail is set for light winds. The loose backstay reduces the mast pre-bend, creating a powerful shape for maximum power. The leech is tensioned for maximum pointing ability.

Upwind – medium conditions
(10 to 20 knots true wind speed)

When the wind increases to the medium range, the boat begins to really power up and the crew weight is needed on the windward rail to sit the boat down. This is when we need to change gears and flatten out the sails to reduce drag, improve boat speed and point higher.

The backstay should be pulled onto a medium tension which flattens out the mainsail. This also helps to tighten the forestay which automatically flattens the entry on the headsail. The luff tension on both sails should be increased to keep the draft at their designed positions. Be careful to not over tension the luff on the mainsail as this can cause excessive back winding by moving the draft to far forward. Having just enough tension to remove the horizontal wrinkles in the luff seems to work well on most mainsails. The headsail luff also needs just enough tension to remove the horizontal wrinkles at the luff tape for luff foils or just enough tension to remove the sags between the hanks on hanked headsails.

The traveler should be positioned so the boom is on or slightly to leeward of the centre line. The mainsheet hand needs to work it up and down through the gusts to keep the boat on the correct angle of heel. The mainsheet should be trimmed to have the upper leech ribbon almost flowing as this helps with higher pointing ability.

The genoa cars need to come aft when the boat becomes overpowered as this will flatten the foot area and exhaust the upper leach. The genoa sheet should be tensioned to keep the leech at approximately 20mm from the spreader.

The helmsperson needs to steer as efficiently as possible to keep the boat moving and to keep the boat’s speed up. Many helmspeople make the mistake of pinching up and pointing too high, which results in them losing boat speed. When that happens the boat slows down, it reduces the lift generated from the keel and it increases the boat’s leeway. It is important that the helmsperson keep the speed up. Crew should sit on the windward rail to sit the boat down to reduce excessive heeling and present the maximum sail area to the wind.

3windwardmedium1lowres‘The sail has a full, powerful shape and the genoa cars are forward to the optimum sheeting point – note the distance between the spreaders and the leech.’

4windwardmedium2lowresThe headsail is set for medium to heavy conditions. The backstay is on to straighten the forestay and flatten the entry. The genoa cars have been moved aft to twist off the upper leach.

Windward – heavy conditions
(20 to 30 knots true wind speed)

In strong winds it’s important to reduce the drag from your sails even further by flattening out the fullness as much as possible and twisting the leeches to reduce excessive heel.

The backstay should be tensioned for maximum mast bend, so the mainsail starts to blade-out (giving you maximum flatness). You can tell if the backstay is tensioned on too much as the mainsail will get quite pronounced creases running diagonally from the luff to the leech, these are referred to as ‘over-bend’ creases. Over-bend creases will also result in your mainsail leech twisting-off or laying-off, which will reduce your pointing ability considerably. If you see these over bend creases starting to appear, ease the backstay until they just disappear and this should be your maximum backstay tension.

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.e. Back winding. 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 to300 to 400 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.

5heavymaintoplowresThe mainsail is set for medium to heavy conditions. The backstay is on to straighten the forestay and flatten the entry. The genoa cars have been moved aft to twist off the upper leach

6heavymainbotlowresThese are mast over-bend creases taht indicate the backstay is on too hard. This occurs when mast bend exceeds the sail’s designed luff curve.


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.e. 40 to 80 degrees off the wind. 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.

Boats that don’t have the budget for these specialist reaching sails must rely on their existing headsails for the reaching legs. The true wind angle we are covering in this section is 38 to 95 degrees True wind Angle.

Reaching – light conditions
(2 to 12 knots true wind speed)

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.

Reaching – medium conditions
(12 to 25 knots true wind speed)

When the wind increases to the medium range it is important to trim the sails to eliminate excessive weather helm on the rudder and to ensure the boat isn’t heeling over too much, as these two factors will slow the boat. 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.

Reaching – heavy conditions
(25 to 35+ knots true wind speed)

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. It is important to keep control of the boat, so reduce sail where needed and the boat will sail much faster with less drag.

In medium to fresh conditions jib staysails can increase your boat’s performance considerably. The staysail sets up inside the jib and creates another slot, which powers the boat up. It is important not to over sheet the staysail. We always set it up with the upper tell tales just lifting, which requires your cars to be up further aft. Over-sheeting the staysail will stall the main and create excessive back-winding. If your boat doesn’t have an inner forestay to hank the staysail to, then the luff can be fitted with a vectran luff rope which acts like a forestay. Your halyard should be tensioned to minimise excessive sag.

The backstay and outhaul have been pulled on to flatten the sail and depower it to reduce excessive heeling and weather-helm. The mast is pulled back and the leech is slightly twisted.

A quick reference
If you’re interested in improving your boat speed then you’ll need to practice and refine these settings for your own boat. Experiment with what I’ve written, learn to read your sails and your rig – after a while it’s as easy as reading a book. “That’s the right amount of twist, or my luff tension is too tight, or my forestay is sagging too much.” Pretty soon you’ll get the hang of it. To help you apply these lessons I’ve included a quick reference card. The next time you’re out on the water take note of the wind conditions, your boat speed and the rig set-up. Establish a baseline, then use this card to begin making adjustments. You should see a good improvement in your speed. From there it’s a matter of marking those set-ups to make them easy to replicate.


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