Sail Trim Is Not “Pull It In Until It Looks Right”
Two boats can have identical sails and completely different speeds.
Put two identical dinghies side by side, give them the same sails, the same wind and broadly similar crews, and one can gradually sail away from the other.
Nothing obvious appears to be wrong.
Both boats are pointing in roughly the same direction.
Both mainsails are full.
Both jibs look reasonably tidy.
Neither crew appears to be making a terrible mistake.
And yet one boat is simply faster.
Quite often, the difference is sail trim.
One crew has pulled the sheets in until the sails look approximately right.
The other crew is constantly asking:
What is the air actually doing?
That is a very different approach to sailing.
For me, this becomes particularly noticeable when crewing an RS Toura or sailing aboard the A-Rater Champagne. Working the jib can sometimes feel rather like operating the boat's turbocharger. A surprisingly small adjustment can change the power, acceleration, heel and even the feel of the helm.
Sail trim is not something you set once.
It is something you continually adjust.
A Sail Is an Aerodynamic Surface
A sail is not simply a piece of cloth that catches the wind.
When a sailing boat is reaching or sailing upwind, the sails behave much more like aerodynamic wings.
Air flows around both sides of the sail and the curved shape helps generate a force that can be resolved into:
a component driving the boat forwards;
a sideways component resisted by the centreboard, keel or hull.
For that process to work efficiently, the airflow has to remain reasonably well attached to the sail.
If the sheet is too loose, the sail may flap or the airflow around it may be poorly organised.
But pulling it in too far does not solve the problem.
An over-sheeted sail can also disturb the airflow.
This is one of the first important lessons in sail trim:
Tighter does not automatically mean faster.
The Beginner's Natural Instinct
When learning to sail, there is a natural tendency to pull a sail in until it stops flapping.
That is actually a perfectly sensible starting point.
Ease the sail until it begins to luff.
Then pull it back in until the luff just disappears.
For a beginner, that simple technique works remarkably well.
The problem comes when we unconsciously add another 10 or 20 centimetres of sheet because the sail somehow looks more secure.
The sail becomes flatter against the centreline of the boat.
It looks neat.
It looks powerful.
But it may actually be slower.
The sail is not there to look tidy.
It is there to manage airflow.
Tell-Tales: Tiny Pieces of Wool That Tell a Big Story
One of the simplest ways of finding out what the air is doing is to look at the tell-tales.
These small pieces of wool, ribbon or lightweight material can give an immediate indication of the airflow over the sail.
On a jib there are commonly tell-tales positioned on both sides of the sail near the luff.
When sailing upwind efficiently, we generally want the tell-tales on both sides streaming backwards reasonably smoothly.
If the windward tell-tale rises repeatedly, the boat may be sailing too close to the wind for the current trim.
The helm may need to bear away slightly, or the sail trim may need reconsidering.
If the leeward tell-tale is struggling or lifting, the sail may be over-sheeted for the angle of sailing.
Again, the important lesson is not simply to memorise a rule.
It is to realise that the tell-tales are showing us what the airflow is doing.
They are miniature aerodynamic instruments.
Stop Looking Only at the Bottom of the Sail
There is another trap.
Many sailors look at the lower part of the sail because it is conveniently at eye level.
But conditions several metres above the water can be quite different.
The upper part of the sail matters enormously.
This brings us to one of the most important concepts in sail trim:
Twist
Look up the leech of a well-trimmed sail.
The upper part of the sail will normally be angled differently from the lower section.
The sail is effectively twisted from bottom to top.
This is deliberate.
The wind experienced by the upper part of the sail is not exactly the same as the wind experienced lower down.
Wind speed generally increases with height above the water because the surface slows the air nearest to it.
The apparent wind experienced by different parts of the sail can therefore vary.
If we tried to force every part of the sail to exactly the same angle, some parts might work efficiently while others stalled.
Allowing the sail to twist lets different heights of the sail operate at more appropriate angles to the local airflow.
Watch the Leech
The leech is the trailing edge of the sail.
Its shape can tell us a great deal about trim.
A leech that is pulled excessively tight can become hooked towards the centreline of the boat.
That can interfere with the air trying to leave the sail.
Instead of producing clean flow, we can create extra drag.
On the mainsail, tell-tales near the leech can be particularly useful.
If the upper tell-tale is permanently disappearing behind the sail rather than streaming aft, the top of the sail may be too closed.
The answer may be to allow the leech to open slightly.
That could involve easing the mainsheet or altering the other sail controls available on the boat.
Again, there is no magic sheet position.
We look at what the sail is telling us.
The Mainsheet Does More Than Move the Boom
Beginners often think of the mainsheet as a simple control:
Pull it in and the boom comes in.
That is true.
But it is only part of the story.
The mainsheet can also affect leech tension and therefore the amount of twist in the mainsail.
On many dinghies, pulling the mainsheet hard while sailing close-hauled does not simply move the boom towards the centreline.
It also pulls downwards.
That can tighten the leech.
The upper part of the sail closes.
Sometimes that is exactly what is required.
Sometimes it is the reason the boat suddenly feels heavy, slow and difficult to steer.
This is why blindly pulling harder can be counterproductive.
The Jib Sheet Is Not Just an On-Off Control
The jib deserves just as much attention.
In some ways, I think of the jib as the boat's turbocharger.
That description is not technically literal, of course, but it captures the sensation remarkably well.
Trim the jib correctly and the boat suddenly feels as though it wants to accelerate.
Trim it badly and the whole rig can feel lifeless.
When I am working the jib, particularly in changing inland conditions, I rarely want to think:
"The sheet belongs here."
Instead I want to think:
"Does the sheet belong here now?"
There is an important difference.
A gust arrives.
The boat accelerates.
The apparent wind changes.
The boat heels.
The helm responds.
And the correct sheet position can change with it.
The Main and Jib Work Together
It is tempting to think of the jib and mainsail as two separate engines.
They are not.
The airflow around one affects the other.
The slot between the jib and mainsail is particularly important when sailing upwind.
Pull the jib in much too hard and the gap can become too restricted.
The airflow through the slot may be compromised and the back of the mainsail may show signs of disturbed flow.
Ease the jib too far and it may no longer be operating effectively.
The aim is not to create the smallest possible gap between the sails.
The aim is to create an efficient aerodynamic system.
This is where a crew trimming the jib becomes much more than somebody holding a rope.
The jib trimmer can be continuously watching:
luff tell-tales;
leech shape;
heel;
changes in wind strength;
the relationship between jib and mainsail;
acceleration after a gust or tack.
That information can then be passed to the helm.
On a larger or faster boat, this teamwork becomes increasingly important.
Light Winds: Do Not Strangle the Sails
Light wind creates a particularly interesting problem.
The temptation is often to pull everything tight in an attempt to extract every last bit of power.
That can be exactly the wrong thing to do.
In very light conditions there is little energy available in the airflow.
A sail that is over-sheeted can make it difficult for that weak airflow to remain attached.
The boat can feel sticky and reluctant to accelerate.
Often the better approach is to allow the sails to breathe.
Ease slightly.
Maintain shape.
Keep the boat moving smoothly.
Avoid unnecessary rudder movements.
And watch the tell-tales carefully.
A centimetre or two of sheet movement can sometimes make a surprising difference.
This is also why stopping the boat in light winds is so costly.
Once moving, the boat creates its own apparent wind.
Lose that motion and the entire aerodynamic system weakens.
Moderate Winds: The Boat Comes Alive
Moderate winds can make trimming easier because there is enough airflow for the tell-tales to respond clearly and enough power for changes to become noticeable.
This is an excellent time to experiment.
Try easing the jib very slightly.
What happens to boat speed?
What happens to pointing?
What happens to heel?
Pull it back in.
Does the boat feel more powerful?
Does the helm become heavier?
Does the leeward tell-tale start misbehaving?
Rather than thinking of sheet position as right or wrong, think of it as an experiment.
Change something. Observe the result.
That is one of the quickest ways to become a better sailor.
Stronger Winds: Power Is No Longer the Only Objective
Once the wind increases, the problem changes.
We may already have more power than we can efficiently use.
Now sail trim becomes partly about depowering.
If the boat is heeling excessively, simply fighting harder against it is not necessarily the fastest solution.
We can change the sail trim.
The sails can be flattened.
The leech can be allowed to open.
The sheet can be eased during stronger gusts.
The objective is to keep the boat driving rather than allowing it to become overloaded.
This connects directly with another important sailing principle:
Keeping the boat reasonably flat is usually fast.
Excessive heel can increase drag, reduce centreboard efficiency and produce heavy weather helm.
Correct sail trim helps prevent that situation before it develops.
The Gust Arrives — Your Trim May Need to Change
Imagine we are sailing upwind and see a dark gust line approaching across the water.
Before the gust arrives, everything may be nicely balanced.
Then the pressure hits.
The sails suddenly produce more force.
The boat heels.
The helm loads up.
What should happen?
Perhaps the crew moves weight.
Perhaps the mainsheet is eased.
Perhaps the jib is adjusted.
Perhaps the helm changes course slightly.
The exact response depends on the boat and the conditions.
But the important point is this:
The trim that was correct five seconds ago may not be correct now.
That is why good sail trim is active rather than static.
Then the Gust Passes
The reverse problem occurs when the gust disappears.
Imagine easing the sails during a strong puff and then forgetting to trim them again.
The pressure falls.
The boat becomes underpowered.
Speed drops.
Someone wonders where all the performance went.
The answer may simply be that the sails are still trimmed for the gust that disappeared ten seconds ago.
This constant cycle is especially noticeable when sailing inland.
The wind over rivers and small lakes is rarely completely steady.
Trees, buildings, banks and surrounding terrain all influence the airflow.
The crew may therefore be trimming frequently.
Not wildly.
Not constantly hauling metres of rope.
Often the movements are surprisingly small.
But those small corrections accumulate.
Champagne Makes This Particularly Interesting
The A-Rater Champagne makes sail trim especially fascinating.
An A-Rater is a very different proposition from a conventional training dinghy.
Its long, fast hull and substantial rig mean that changes in power can become immediately noticeable.
There is also considerably more going on than simply asking whether the sail is flapping.
When the boat accelerates, the apparent wind changes.
When the apparent wind changes, the ideal sail trim changes.
When the sail trim changes, the boat may accelerate again.
So there is a feedback loop.
That can make working the jib enormously rewarding.
When everything comes together, the boat does not merely feel as though somebody has pulled another rope.
It feels as though the whole boat has suddenly been released.
That is the sensation behind my description of the jib as the turbocharger.
The RS Toura Teaches the Same Lesson
The RS Toura offers the same underlying lesson in a rather different way.
It is an excellent platform for noticing how coordinated crew work affects the boat.
The helm can concentrate on:
course;
balance;
wind shifts;
other boats.
The crew can watch:
jib tell-tales;
sheet tension;
approaching gusts;
boat heel;
sail shape.
Instead of waiting for the helm to say:
"Can you ease the jib?"
the crew begins to anticipate the requirement.
That is when sailing starts becoming genuinely collaborative.
The boat begins to feel as though it is being sailed by a team rather than by one person steering while everybody else follows instructions.
A Simple Exercise: Deliberately Get It Wrong
One of the best ways to learn sail trim is deliberately to make mistakes.
In suitable conditions and with plenty of clear water, sail on a steady course.
First, pull the jib sheet too tight.
Observe:
the tell-tales;
boat speed;
heel;
helm feel.
Then ease it too far.
Observe the same things.
Finally, gradually trim towards the point where the airflow looks best and the boat feels fastest.
Do the same with the mainsail.
This is extremely valuable because students begin to associate what they see with what they feel.
A textbook can tell you that a sail is over-sheeted.
Actually experiencing an over-sheeted sail teaches the lesson much more effectively.
Use the Boat as an Instrument
Eventually, you should not need to stare at the sails every second.
The boat itself begins providing clues.
Has the tiller suddenly become heavy?
Has the boat stopped accelerating?
Has the heel increased?
Has the bow started making more wash without any obvious increase in speed?
Has the boat suddenly felt lively after a tiny ease of the jib?
These are all pieces of information.
Good sailors gradually combine:
what they see + what they feel + what the tell-tales show + what the boat does
That is sail trim.
Do Not Chase Perfection Every Second
There is another important point, particularly for sailors who are still learning.
You do not need to spend the entire sail frantically moving sheets by millimetres.
The aim is not nervous constant adjustment.
It is awareness.
If the wind is steady and the boat feels fast, leave things alone.
When the conditions change, respond.
The better you become, the earlier you notice those changes.
You may see the gust on the water.
You may feel the pressure change through the sheet.
You may notice a tell-tale beginning to lift.
Eventually the adjustment happens almost automatically.
Sail Trim Is Really Airflow Management
The phrase “trim the sails” can make the process sound like tidying them up.
But that is not really what we are doing.
We are controlling aerodynamic surfaces.
We are trying to maintain useful airflow.
We are adjusting power.
We are controlling heel.
We are responding to apparent wind.
And we are balancing several parts of the rig so that they work together rather than against one another.
The mainsheet is not simply a rope that pulls the boom in.
The jib sheet is not simply something that stops the jib flapping.
The tell-tales are not decorative pieces of wool.
And the leech is not just the back edge of the sail.
They are all part of an aerodynamic system.
That is why two boats with identical sails can travel at completely different speeds.
One crew may have pulled the sheets in until everything looks right.
The other crew is still listening to what the sails are telling them.
And very often, that is the boat sailing away.
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