Sail trimming - tell tales, controls, sheeting and the secret of speed
The secret of speed - this is the bit everyone is looking for!
Well it’s simple. The secret of speed is simply the correct amount of twist in the sails.
To get there, first you have to be accurate in your steering. If you wander your course more than about 5 degrees you will never get the last bit of accuracy that is required. Staying within a steering window of about 2 degrees, only then can you optimise everything!
Those little ribbons stuck on your sails are critical for the “secret of speed”.
Airflow is everything to a sailboat and without it, you are going nowhere! So it stands to reason that the more efficient you are, the faster you will travel.
Sails are just aerodynamic wings so you need to understand a few things.l
Luff, the leading edge of the sail
Leech, the training edge of the sail
Between those two,
Camber, the amount of curvature in the sail
Draft point, the point of maximum depth (camber) of the sail expressed as a % aft of the leading edge.
The Luff is the (leading edge) that cuts the airflow.
The Leech (trailing edge) releases the airflow off the surface.
The Camber is responsible for the amount of power the sail can have i.e more camber = more power but, more Camber also = more drag!
The draft point will determine the overall efficiency of the sail (wing) as far as aerodynamics go, a draft point 30% aft of the leading edge is deemed to be efficient.
With all that in their heads, a sail designer has to understand the rig/boat that the sail will be attached to and on top of that, the sail designer must understand the bend characteristics of the mast. Get any element wrong and the chance of having a ‘fast’ sail is greatly diminished.
How it works
Due to the curvature of the surface of the sail, low pressure air develops over the leeward side of the sail with the ‘high’ pressure on the windward side of the sail. As things try to balance out, there’s a force from high to low pressure and so, the boat is being sucked along rather than pushed along.
The Tell Tales allow you to see the airflow over the sail and so as you sail a course heading you will need to keep an eye on the tell tales.
Air wants to flow in the path of least resistance and by presenting a barrier (sail) to the wind, we force it to bend around the sail. When it comes to sheeting, oversheeting totally kills all airflow and undersheeting will just mean you sail a little slower so, undersheeting a little is the lesser of the evils.
As air flows over the sail it does not flow horizontally back as most people imagine.
It meets the leading edge then passes back and slightly upwards as it comes to the draft point after this point, it rapidly drops away. So rather than flowing straight back it has a ‘hump’ in it. This is the reason aeroplane wings developed winglets to keep the air flowing in a straight manner.
Translate this to the tell tales, keep the leeward ones flowing horizontally and the inner ones (windward side) agitating from horizontal to about 45 degrees up, agitating up to horizontal.
Mainsheet: The mainsheet is an 8:1 system. It’s highly geared to deal with the huge loads that our sails develop. The movement of the mainsheet is more vertical than it is horizontal and so the mainsheet is responsible for twist in the mainsail and twist is the secret to speed!
Main traveler: The traveler is the track that runs across the cockpit. This is responsible for the horizontal movement of the main sail.
Jib sheet: Use this to control the tell tales in the sail. Hard on upwind and eased off the wind.
Jib track: Use this to control the twist in the jib. Forward for less twist (offwind) aft for more twist (upwind). We also use this to adjust the sail for stronger winds, aft and more twist to depower the jib in the head of the sail.
Spinnaker: Use this to control the luff of the sail or if you have tell tales in your spinnaker, trim to those. We use an additional tweaker system to control the amount of twist - but leave that for a more advanced stage.
Screecher: The most powerful sail in the wardrobe. If people are going to scare themselves this is usually the sail to do it!
Corsair 750/760: the sheet comes to a block on the gunwhale of the mainhull and close to the cabin. This is a very ‘tight’ position and great for tight reaching in light/medium air. But it’s going to power the boat up too much for beginners in medium + winds. We use a block that is affixed to a point about half way out the trampoline. We suggest this is a safer place to keep it until you have a good feel for the screecher.
C28/31/970: all of these have the screecher block strapped to the rear beam approximately half way out. This is a good all round point, Corsair 750/760 beginner please note!
When you come back for more advanced training, install a tweaker and learn to control the twist in the screecher over the whole wind range and you will be much better off.