Sail Trim for Cruisers
There are stacks and stacks of articles and books on sail trim written from every possible perspective. One would be foolish to hope to cover it in any depth in a single article, but hey when did we ever stop because something seemed a foolish endeavor?
This article will cover all the major concepts on sail trim and theory but only on a level deep enough to empower you to sail your boat faster, more comfortably, and to deal with heavy weather in a more effective manner. The primary goal is to dilute the theory and practice to very simple steps that will help you understand sails, sail controls and how to optimize sail trim, speed and balance for your boat as a Cruiser.
The Table of Contents for this article is listed here. Understanding all the basic concepts of aerodynamics and sail theory wont necessarily make you a better sailor, but understanding these allows you more ability to problem solve for yourself since you will have an understanding of the forces involved in making your boat move and how to effectively harness them. That said, if you understand the terms and terminology of sails, controls and shape you can jump right to the Sail Trim Cheat Sheet to see simple, clear and effective step by step approaches to make your boat faster, more efficient and safer.
I welcome any and all feedback on this article, it is intended as an "Evergreen" article that will be continually updated and improved over time and hopefully with the feedback of those who have read it.
Now time to jump right in...
Before we can proceed we need to ensure we are using the same terminology to mean the same things so lets cover the basic terminology of the parts of a sail.
There are three sides and three corners to a Mainsail and Headsail.
Next: Sail Controls
Most controls have more than one effect and understanding what these effects are for each control and how to utilize them is critical to understanding and executing effective sail trim.
In the previous section we show that all headsails and mainsails have a leech, luff and foot. There are controls for each of these sides that loosen or tension the side affecting the shape of the sail and the air flowing over it.
Below are a list of the controls on mainsails and headsails.
Cunningham or Downhaul
- Boomvang (Kicker)
Downhaul (on some boats)
- Fairlead Position
Most sail controls have a more than one effect on the sail shape. There can be overlapping actions from different controls as well. Some examples below illustrate the complexity of the effects a single sail control may have.
The backstay, when tensioned, de-powers the sail plan. It does this by bending the mast forward in the middle and aft at the top. This has multiple effects:
- Bending the middle of the mast forward decreases the draft in the mainsail (flattens the mainsail by taking some of the curve out of it). Less draft = less power.
- Pulling back the top of the mast:
- Opens up the upper third of the mainsail's leech which falls to leeward spilling air and pressure. This is called "Twist" and will be covered in detail later. Increasing twist has a powerful effect on reducing heel since the effect happens mostly near the head of the mast where the wind exerts the most leverage.
- Tightens the headstay and headsail halyard which flattens the headsails draft and shifts it forward, depowering the headsail and changing its center of effort.
Example: Main Sheet
The mainsheet also has a multitude of effects. It does not simply bring the mainsail towards and away from the centerline of the boat, it also has a vertical component to its effect.
The mainsheet is connected to the boom and when you tension or ease the mainsheet the boom moves towards or away from the centerline of the boat. This changes the angle of attack
of the main sail.
Angle of Attack is the angle between sail's chord and the wind.
When you sheet the sail closer and closer to centerline you are also increasing the downward pressure on the boom. The closer the boom is to the centerline the more the downward pressure is exerted. At a given point, depending on the wind pressure, any additionaly tension on the mainsheet no longer moves the boom towards the center but only pulls it down - increasing tension on the leech of the sail and decreasing twist.
It is this complex and frequent overlap of effects that prevent many cruisers and sailors from fully understanding what is happening to their sails, how it affects their boat speed, and what to do to optimize sail trim.
Sail Controls and Their Effects
Below are a list the the main sail controls and the effects they produce on sails when adjusted. In the following sections we will discuss twist and draft in detail and then on to the specifics of how to trim your sails.
- Lines attached to boom that are used to change the sails angle of attack (move the sail towards or away from the centreline of the boat). An additional effect is that they also change the tension in the leech of the sail which changes the amount of twist in the sail.
- Jib Sheet
- Lines attached to the clew of the headsail that are used to change the sails angle of attack (move the sail towards or away from the centreline of the boat). An additional effect is that they also change the tension in the leech of the sail which changes the amount of twist in the sail.
- Fairlead Cars (Headsail Only)
- Fairlead cars are movable blocks attached to the fairlead track that move forward and aft. The jib sheet is run through them and by moving the fairlead car forward or back you change the vertical angle that the sheet pulls on the headsails, this changes the amount of downward pressure on the leech which in turns changes the amount of twist in the sail.
- Line used to raise a sail. It is also used to change the tension on the luff of the sail which moves the draft of the sail forward or back
- Line with one end generally attached to the transom of a boat and the other to the top aft end of the mast. When tensioned it has multiple effects: It bends the middle of the mast forward decreases the draft in the mainsail (flattens the mainsail by taking some of the curve out of it) and pulls back on the top of the mast increasing twist and increasing forestay tension which also flattens the headsail and moves the headsail draft forward.
- Cunningham / Downhaul
- Generally only on the mainsail but can be found on headsails as well. Serves the same purpose as the halyard by increasing or decreasing tension on the luff of the sail and moving the draft forward and back. It is a more efficient method of doing so than adjusting the halyard and can be run with a significant amount of purchase (as much as 20 to 1) so that it can be adjusted easily from the cockpit.
- Outhaul (Mainsail)
- Line to the clew of the main sail that tensions the foot of the sail. This control has a greater effect on the lower part of the main than the upper and is designed to reduce draft.
- Boom Vang / Kicker (Mainsail)
- A block and tackle or hydraulic based device that controls the booms vertical angle. Increasing or decreasing boom vang tension increases or decreases the amount of twist in the mainsail in a similar manner to the mainsheet.
- Traveller (Mainsail)
- A track on the deck of a boat that stretches from port to starboard that the mainsail block and tackle connect to. It is used to move the sail in or away from the centerline without changing the tension on the mainsheet and therefore maintains the sails shape while also changing the angle of attack. This is the first option to use when a boat has to much weather helm.
Next: Sail Aerodynamics
We have covered the terminology of sails and the controls that change sail shape now we will cover how sails work and basic aerodynamics. The following section should illustrated the importance of "Attached Flow", keeping the flow of air moving uninterupted across the surface of the sail to maximize life and power. In the following section we will talk about how to manage that power.
To help with terminology and understanding about why minute adjustments to sails can make such a big impact on sail performance as well as comfort on a boat we will touch on some basic sail aerodynamics and theory.
Sails work with wind in two manners: Attached Flow and Stalled Flow.
Sailing dead downwind or nearly dead downwind is utilizing stalled flow for power. Stalled flow as a form of sailing has been around for millennia and is basically the process of letting the wind push the boat, the manner in which the old square riggers would primarily use for sailing. Boat speed in this type of sailing is a direct result of the amount of surface area of sail presented to the wind. Approximately 90% of the force applied by the wind is translated into effort and the combination of this force and the drag present by the sail and hull shape will give you your maximum speed.
For the purposes of this article we will be focusing primarily on attached flow.
Attached flow is the process of air moving over both sides of a sail to generate lift.
Sails work on the same principles as airplane wings. Both are airfoils and generate lift in an identical manner as explained by the Bernoulli Principle.
Where the velocity of a fluid is high, the pressure is low.
Where the velocity of a fluid is low, the pressure will be high.
As you can see from the illustration the wind has to travel a longer distance along the curved part of the wing than it does the flat part of the wing. According to Bernoulli there are two things at play here:
1. Imaginary Particle A and Imaginary Particle B arrive at the leading edge of the wing at the same time in the flow of air. They must also depart the trailing edge at the same time if the flow of air is uninterrupted along the surface of the wing.
2. Since both imaginary particles must start across the leading edge of the wing and leave the trailing edge of the wing together and Particle A has a longer distance to travel, then Particle A must increase its velocity. To do so the airstream "thins out" and creates at low pressure bubble on the curved part of the wing. This acts just like a vacumn and pulls the wing towards the low pressure. In the case of an airplane it pulls upwards, in the case of a sailboat it pulls it forward. Well, it pulls it slightly forward of perpindicular to the sails chord and the forces of the keel compensate and pull the boat forward but we will cover that in the upcoming section; Balance of Forces. For now lets agree that it pulls the boat forward.
Sails and Lift
To the right is a diagram of a sail. You can see that the shape is basically the same as the wing but this is a thin foil - there is no bottom flat surface as there is on a wing. By comparing the two images you can see that the differences in distance traveled by the split airflow over a wing's surface are greater than the differences in distance traveled over a sail's surface. These differences illustrate the differences in efficiency between a sail and a wing, a wing generates substantially more lift than a sail even though they both operate almost identically.
In general a sail generates 2/3 of its lift from the low air pressure on the leeward side and 1/3 from the direct wind pressure on the windward side.
Draft, Lift and Drag
Both an airplane wing and a sail have the ability to increase or decrease the amount of lift they generate and they both do it in generally the same manner - they increase or decrease the draft of the airfoil.
Given that an aircraft wing is constructed out of rigid aluminum they are unable to change the shape of the wing itself, instead they utilize flaps that change the length of the chord of the foil and the draft of the foil. This has the effect of increasing lift but also increases the amount of surface presented to the wind and increase drag. For an airplane they only want enough lift to keep the plane moving horizontal to the earth at a given speed. As the speed increases they require less lift, as speed decreases they require more lift.
Increased Lift = Increased Drag
For an airplane too much lift and drag equals excessive use of power and fuel to maintain a given altitude and speed. For a sailboat too much lift means the boat will heel excessively, too much drag means the sail plan is not optimized for the given wind speeds and will underperform.
In the diagrams to the right you can see the differences in a sail with a shallow draft and one with a deep draft.
Similar to an airplane, a sailboat only needs enough lift to reach its optimal hull speed. Excess lift in a sailboat manifests itself as excessive leeward drift and heeling. Lucky for us our airfoil is made out of soft material and to change lift is simply a matter of changing the draft of the sail itself using the tools at our disposal.
How to modify draft and increase or decrease lift and drag to meet given wind conditions is one of the 3 Elements of Sail Power one must understand to optimize sail trim.
3 Elements of Sail Power: Angle of Attack, Draft and Twist
We have discussed the tools that control sail shape and basic sail aerodynamics and how sails work to generate lift and power. Now we are going to cover the 3 Elements of Sail Power and how they each work together to maximize speed and comfort; Angle of Attack, Draft and Twist. Once you understand these and the concept of Balance of Power you will be ready to take this knowledge into practice and we will switch gears to discuss the use of telltales, heel, and helm as tools to inform you how to apply this knowledge.
Next: Angle of Attack
Angle of Attack
Angle of Attack (AOA for the purposes of this article) is the easiest of the 3 Elements of Sail Power to conceptualize. Any sailor who is able to move their boat upwind to a destination is utilizing AOA to generate power.
As mentioned in the previous section, AOA is the angle between the direction of the wind and the chord of the sail.
Changing your AOA is as simple as changing the boat's orientation to the wind by changing course or changing the sail's orientation to the wiind by using the mainsheet.
Lets look at three examples of AOA:
- AOA Too Large- Over trimmed Sail
- AOA Too Small - Under trimmed sail
- Proper AOA - Correct trim for wind angle
AOA Too Large
When the sail is trimmed too close to the centerline of the boat for the given wind angle then the wind is unable to flow along both the windward and leeward sides of the sail. Initially as you increase the AOA beyond optimal trim the air flow begins to detach along the leeward side of the leech, on the mainsail this can be seen by the leech telltales flowing backward behind the sail. As you continue to increase the AOA further a seperation bubble will be created along the leeward side of the luff of the mainsail. This is extremely detrimental to the sails ability to generate lift and power.
AOA Too Small
When the sail is trimmed to far away from the centerline of the boat for the wind angle then the wind begins to detach from the inside near the luff creating a separation bubble and also detachs from the leech. This can be seen by the well known effect of "Luffing". Luffing starts along the luff and gradually more and more of the sail begins to luff as the sail's AOA gets smaller and smaller until the sail is pointing straight into the wind and luffing like a flag on a pole. There are times where the front 10-30% of sail will invert with the pressure of the separation bubble. This is not as detrimental to boat speed as over-trimming and we will discuss in later sections how to utilize this effect depower the sails in heavy weather conditions.
Attached flow of air across the entire surface of the sail begins with trimming the sail to the correct AOA. The correct AOA will vary from sail to sail, will change as you change the shape of the sail, and will change with different wind speeds. Luckily it is relatively easy to identify the proper AOA using your telltales and is simply a matter of taking in or easing out the mainsheet or jibsheet which will be covered in upcoming sections
Next: Understanding Draft
As we mentioned previously in the section on Sail Aerodynamics, Draft is the amount of camber, or curve, in your sail. More draft depth generates more lift.
Quite simply; Easing the halyard, cunningham/downhaul, outhaul and backstay increase draft. Tensioning these same controls decreases draft. However, there is more to draft than just changing the depth of your sail.
How Changing Draft Changes the Sail
Essentially there are two general conditions that require us to change the draft on our sails - too much power and too little power. In light airs we want to carry as much draft as possible so that we can reach hull speed and in heavy air we want to remove as much draft as possible to remove the excess power that manifests as weather helm, heel and excessive leeward drift. You can also adjust the draft position fore and aft to change the center of effort of the power in the sails to assist in balancing the boat and minimizing weather helm.
In the section on Sail Controls we explored the concept of Multiple Effects. With the exception of the outhaul, all the controls that affect the depth of the draft on a sail also have other effects to the sail plan. Much of what we will cover in this section will apply to all other aspects of sail shape in addition to draft.
Elements and Ratios of Draft
To discuss sail shape and how changing the sail controls that relate to draft change the shape of the sail we need to use the correct terminology. There are three elements that are used to generate two ratios related to calculating the aspects of Draft in a sail. We will use these in detail in this section to explain what happens to a sail when the sail controls that affect draft are manipulated.
- The length of an imaginary straight line drawn from the luff to the leech of a given section of sail.
- Draft Depth
- How deep the curve of the sail is in relation to the Chord. The Chord is an imaginary straight line drawn from the luff to the leech.
- Draft Location
- The distance from the luff of the maximum depth in a sail along a given section . It is written as a percentage of the distance from the luff to the leech.
Draft Position = (Draft Location/Chord)%
Camber Ratio = Draft Depth / Chord
Draft and Sail Shape
Lets look at some examples where a mainsail is adjusted for Light Air and Heavy Air. In the following illustrations the changes that would occur to the sails has generally been exaggerated for the purposes of clarity.
In conditions where your boat is not reaching hull speeds more draft is always better - up to a point. This is where one of the ratios comes into play, the Camber Ratio. Maximum lift is acheived with a camber ratio of approximately 20%. If the depth is increased any further the wind speeds on the leeward side of the sail increase to the point where they detach, stall or even flow against the prevailing apparent wind, causing a loss in lift.
See the following example. A section of the sail has a chord of 300cm and a depth of 60cm, the camber ratio is 20%. This type of depth would be more likely found on large genoas than on small head sails or main sails.
To maximize lift you want a flat entrance angle on the luff of your sail in addition to a deep draft. To acheive this you shift the draft as far aft as possible. As we mentioned in the section on Sail Aerodynamics increased camber and a large angle of attack (AOA) increases lift.
Mainsail Set for Light Air
In this illustration we have set the sail to generate as much lift and power as possible:
- Maximize AOA: Draft Position is shifted as far aft as possible which flattens entry angle and maximizes AOA for any given trim angle
- Maximize Draft: The sail is set as full as possible and in the process the leech is hardened decreasing twist (to be discussed in the following section)
When your boat is overpowered in strong winds we want the sails as flat as possible and the draft location shifted as far forward as possible, this decreases the lift in the sail and broadens the angle of entry of the sail to allow the sail to be further away from the centerline for a given wind angle (smaller angle of attack) and still maintain airflow. The overall effect by decreasing angle of attack and decreasing lift when the boat is overpowered is to reduce heeling moment and weather helm.
Mainsail Set for Heavy Air
In this illustration we have set the sail to minimize lift and power:
- Minimize AOA: Draft Position is shifted as far foreward as possible which broadens entry angle to allow sail to be eased off which decreases AOA and spills power
- Minimize Draft: The sail is flattened as much as possible and in the process the leech is also opened up increasing twist to spill additional power from the top part of the sail (to be discussed in the following section)
Why is there a difference in entry angle and camber ratio as you move up the mast?
Wind is very sensitive to friction and turbulence. On a 40' sailboat with a 60' mast, the wind speed can be 30% faster at the mast head than at the foot of the sail. This is due to the friction present when the wind blows over the water. The increased wind speed creates what is known as a velocity header as you move towards the tip of the mast, with an increasing angle of attack the closer one moves towards the tip of the sail. AOA at the foot of the sail may be 20° while at the head it may be 45°.
Wing Tip Vortex
The modern marconi or bermuda rig, what most of us sail, utilizes a triangle sail plan that is similar in shape to an airplane wing. Like an airplane wing it experiences an effect called Wing Tip Vortex.
As you near the tip of the sail, similar to the tip of an airplane wing, you being to see the angle of the wind change. The angle changes both horizontally and vertically. First, the closer you get to the tip of the sail the more the wind flows towards the tip instead of directly across the sail surface. Near the tip it can be flowing as much as 45° above horizontal - this is known as upwash. This compounds the effects of the velocity header and can change the effective AOA by over 30°.
IMAGE: VELOCITY HEADER AND UPWASH ILLUSTRATION
- discuss draft position and depth changin up the sail and why
- minimize draft depowers to a point - next step - twist lead into next section
- show how down haul/cunningham/halyard affects draft depth and position
- show how outhaul affects draft position
- show how backstay affects position on jib
- understand about optimizing draft based on maximizing lift when beneath the boat and sails optimal wind speeds and optimizing draft when exceeding this speed - i.e. maximize lift and power versus spilling power while maximizing drive
- show sail control effects
- Show AOA changes due to Vortex and Velocity Header
Light Air Controls: XYZ
Heavy Air Controls XYZ
If you take anything away from this section think
Draft = Power
Next: Understanding Twist
- What is twist
- Discuss wind and surface friction - gradient wind
- Explain how trianglular sails twist the wind up to 25-30 degrees as you go higher up the mast
- understand about optimizing twist based on maximizing lift when beneath the boat ans sails optimal wind speeds and optimizing twist and draft when exceeding this speed - i.e. maximize lift and power versus spilling power whil maximizing drive
Twist is not just about spilling powerIllustrate twist with image showing aft view of leech
- show two sails from rear showing heavy twist and less twist side by side comparisons
- show sail control effects
Next: Balance of Forces
Balance of Forces
Discuss the vectors of different boat parts - balance of head sail force and main sail force with keel force and rudder
Illustrate CE and COF with vector drawing
Understanding what your sail is doing is not magic. Racers, who make a series of seemingly obscure minute adjustments to their sails, aren't magicians - they are using cues to tell them what is happening. The main tool at their disposal are telltales.
Telltales feed you information about how the air is flowing, or not, across your sails. Understanding how to interpret your telltales, and more importantly to adjust the sail based on what they are telling you is the key to proper sail trim.
Telltales can consist of many materials from coloured yarn to strips of old magnetic cassette tape. For cruisers you want material that will last longer and storebought telltales made of coloured thin sail cloth or nylon will last the longest and are very inexpensive.
Now, before you go run out and cover your sail with telltales lets talk about their positioning and use.
Where to Install Telltales on Sails
Create a 3 x 3 grid of telltales on each side of the sail. Ideally you want to use different colors on each side of the sail such as red/green to avoid confusion - especially if your sail has windows designed to allow clear vision of the telltales. When using red/green it is recommended to install the telltales on the same sides as their corresponding navigation lights - red on port and green on starboard.
Each set of telltales has a Top, Middle and Bottom telltale. They should be placed as follows:
- 25% of the way down from the head of your sail
- 50% of the way down from the head of your sail
- 75% of the way down from the head of your sail
- Set 1
- Place your first set of tell tales 1' aft of the luff of your head sail and space them as indicated above
- Set 2
- Place this set of telltales mid way between luff and leech
- Set 3
- This set should be 1' forward of leech
You should attach one set of telltales to the leech of the main so that they are streaming aft of the mainsail. They should be spread vertically in the same manner as the telltales on the headsail. This is the only set that should not be in pairs.
If you have battens in your mainsail then each batten should have a telltale. They should be attached to the leech end of the batten pocket. Be careful how you attach them so that there is no bias to the way they stream - this will make it difficult to read them in light airs.
How to Read Telltales
In the examples below we used red and green telltales and placed each telltale on the same side of the sail as their respective navigation light. Red on port and green on starboard. This makes it is easier to identify which telltale needs to be adjusted.
When observing your telltales remember the 4 "T"s:
"Trim Towards The Telltale"
Simply put, the sail needs to be moved towards whichever telltale is not streaming aft, horizontal to the water.
If the telltale is not streaming aft on the leeward side then the sail needs to be eased out, if it is not streaming aft on the windward side the sail needs to be taken in.
It is really that simple.
What is more complicated and something we will discuss further on is the need to adjust different parts of the sail independently of one another to get air flowing over the whole surface.
Here are some examples of telltales:
Properly Trimmed Telltales
This is an example of a properly trimmed set of telltales seen through a "trimming" window that would be found on high performance sails. As we mentioned earlier the green telltale is on starboard and the red telltale is on port. In this case the green telltale is on the windward side and the red telltale is on the leeward side. Note how the windward telltale "green" is streaming slightly lifted above horizontal. This is indicative of perfect trim.
Telltales Without a Window
This is how you would see a majority of your telltales. The one on the leeward side will be seen as a shadow through the sail. Generally it is quite easy to see the telltale - unless you are one of those with tanbark sails - but for the rest of us it is not problematic.
Note how the telltales are attached slightly apart vertically, this makes it much easier to see the flow of the leeward telltale.
Improperly Trimmed Telltale
This is an example of a telltale that is not streaming aft. Air is still flowing across the sail but it is disturbed and the telltale may lift or flutter. The untrimmed telltale is on the windward (starboard) side of the sail, using the 4 "T"s what action should be taken?
(see below for answers)
Improperly Trimmed Telltale, pt. 2
Another telltale that is not streaming aft, this time it is the leeward (port) telltale. Air is not flowing and has detached from the backside of the sail causing the telltale to stall or drop. Using the 4 "T"s on this example what action should be taken?
(see below for answers)
That is the guts of how to trim telltales. They are remarkably effective as a tool and are the primary way to adjust your sails. Understanding how to use them is all you need to optimize your sails. Now lets look at each of the sail controls that let us adjust the sail as a whole and adjust each part of the sail individually.
Improperly Trimmed Telltale: Trim the sail in until the windward telltale starts to stream aft. This moves the sail towards the telltale and towards the wind.
Improperly Trimmed Telltale, pt. 2: Ease the sail out until the leeward telltale starts to stream aft. This moves the sail towards the telltale and towards the lee.
Next: How to Use Telltales and Controls
How to Use Telltales and Sail Controls
Next: Basic Trim Tips for Headsails
Basic Trim Tips For Headsails
All 3 sets on both sides should be streaming aft. Ideally the ones on the windward side should be just “lifting” – ie pointing just above horizontal. Ease the sail towards the tales that are not flying.
To get them all flying you will need to adjust the fairlead. Trim the sail until the bottom tales are flying. If the top tales on the inside are not flying then move the fairlead forward until they do., if the ones on the outside are not flying ease the fairlead back until they do.
Next: Basic Trim Tips for Mainsails
Basic trim tips for Mainsails
Basic trim tip for main upwind:
Tip 1: You want the telltales that are streaming off the leech to be flying 50% of the time. That means you don’t want them streaming hard aft instead you want them to fly, drop, fly, drop about 50% each. This gives you your optimal attached flow and entry angle for the main.
Tip 2: Once you have the tales flying you can optimise the sheet and vang tension based on the angle of the aft end of the top batten.
In light airs (0-8kts) it should point 5-10 degrees to weather (0degrees would be parralell to the boom, this can be seen by looking up the sail from under the boom and once you get used to it you can spot it easily from the helm)
In Med Airs (10kts -15kts) it should point parallel to the boom
In heavy airs 15kts+ it should point to lee of the boom.
Triming the main pulls the batten to weather (once already close hauled) and easing it opens to lee
Tip 3: Use your traveller
To get the above right your traveller needs to be involved. You always want your main as close to the center as possible until it creates too much weather helm. Generally in light air you will have the traveller all the way up on the windward side of the boat and the main centered and in heavy air you will want the traveller all the way down on the lee side of the boat.
Tip 4: Weather helm is dangerous, hard on your equipment and slow – fix it to go fast
When racing you never allow more than 5degree of weather helm going up wind and it is a good idea to stick to that as well when cruising as it will save wear and tear and power drain on your autopilot as well as slow you down.
Next: Quick Solutions to Solve Weather Helm
Quick Solutions to Solve Weather Helm
1. “Drop” the traveller – lower the traveller to lee until the helm feels more balanced
2. Ease the vang, ease the sheet, or tighten backstay – this opens up the leech at the top of the sail and depowers the top of the sail. As this is a long way from the center of effort the power up here creates a lot of heel and even a small depowering by opening up the leech works wonders.
3. Shift the draft of your sails. By tightening the luff of your sails you move draft forward by easing you move it back – you can work this one out on your own boat
Next: Wrap up
- Don't think of your sails as two separate sails - think of them as one large sail
- Flatter in heavy wind, fuller in light wind
Number One Tip: Look at what you are trimming.
If you look at the sail when you are adjusting it you will clearly see what is changing. For example if you look at your main when it is sheeted really hard in and you ease the sheet even a couple of inches you will see a dramatic change in the position of the leech and it is clear what adjusting that line, even a bit does.
FoolishSailor is a Certified USSailing and RYA Instructor and has taught sailing, racing and cruising skills to children and adults for over 20 years in locations as diverse as Japan, San Francisco and Ireland.
Next: Sail Trim Resources for More Details
Sail Trim Resources
So you want more information? Great!
Below are some links that goes into incredible detail on everything from sail design to the physics of sailing, enjoy!
Sail Shape and Theory
Next: Sail Trim Cheat Sheet Download
Sail Trim Cheat Sheet
- Boom Vang / Kicker (Mainsail)
- A block and tackle or hydraulic based device that controls the booms vertical angle. Increasing or decreasing boom vang tension increases or decreases the amount of twist in the mainsail