developed and seo specialist Franco Danese

HOW TO – Quick Guide: how to use your telltales and wind indicators

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boat telltalesTelltales are a very powerful tool to help with sail trim, even of the most “extreme” racers like TP52 (picture above) andAC75 yachts.


A telltale is a piece of yarn or fabric attached to a sail, a stay, or any rigging on a sailboat used as a guide for trimming a sail according to wind direction. An apparent wind indicator, instead, is a small weather vane or arrow that gives an indication of the current apparent wind direction. The following is our quick guide to the use of these essential tools.

leech teeltales

Leech telltales indicate the flow out of the mainsail: they are the first to be adjusted, starting from the uppermost one, maneuvering on the sheet, and descending, maneuvering the vang.


On the mainsail, telltales can be installed on three lines: along the leech, in the middle part, and near the luff. The telltales placed along the leech, at the height of the batten pockets, are the most important ones: they allow the evaluation of the air flow coming out of the whole sail, thus suggesting the overall mainsail performance.

In order to have the perfect mainsail trim, concentrate on the uppermost telltale and trim the mainsheet. In succession, acting on the vang, the other telltales will be correctly trimmed on the leech. The high batten should be almost parallel to the boom. In strong winds, the leech will tend to vibrate, making it impossible to “read” the telltales. In addition to hauling the vang, the duet must therefore be tensioned, the line inside the sail that adds tension and rigidity to the leech.


The telltales in the middle of the mainsail are installed above and downwind. They are useful for adjusting the shape of the mainsail and indicating the presence of turbulent rejection of the headsail.

The median telltales take on special significance when viewed all together, identifying areas with less or more fullness If, for example, fullness is too low, the leeward telltales of the lower part will tend to fall. Hauling the mainsail base will be the first maneuver to improve the sail profile.


When placed on the luff, telltales are used to indicate that the sail is luffing or coming head to wind. They are mainly used on fast boats and dinghies, where the cunnigham greatly changes the shape of the sail in this area. On pivoting mast catamarans, they help orient the mast and full-battens. They also serve to reach the voluntary stall: in the event of strong wind, in fact, on catamarans where you cannot reef, the lift is reduced by counter-rotating the rotating shaft, until the luff telltales do not all go in turbulent motion.


In addition to indicating the correct wind angle as illustrated on these pages, forestay telltales allow to adjust the sheet point. If the windward telltale moves upwards, the sheet point must be moved further, vice versa, the sheet traveler moves backwards. On Code 0, the telltales are already positioned at strategic points in order to clearly indicate when the sail has the optimal angle and shape to ensure maximum performance in low wind conditions.

In nature, on some birds, it seems that the feathers connected to the muscles of the wings perform a function similar to telltales, allowing the animal to constantly correct the airfoil and fly even in gusts.


Spinnakers and gennakers can already been considered as a giant telltale. The bowman trims the sheet. He eases, looking for maximum extension and sudden hauls, looking for a balance between these two points.

On the spinnaker, if the incoming flow is laminar, it will propagate, due to the spherical cap shape along the entire surface. Wind indicators are useful in this case, to indicate the correct direction of the apparent wind. On the gennaker, telltales are similar to the jib ones. Telltales must all be analysed in order to identify possible turbulent interactions. On gennaker-equipped dinghies, where no jib is provided, the incorrect position of the headsail significantly impacts, for example, the leeward gennaker telltakes, while a not well-trimmed mainsail will drastically nullify the outflow of a spinnaker.


Electronic anemometers and Windex indicators have replaced the use of a long ribbon on the mast head as a weather vane. This remains in use only on radio-controlled classes. However, the tapes, often made from old audiocassettes and mounted on the lower shrouds, are useful in various circumstances. In the port, for example, they identify wind turns not present at the mast head: the wind impacting the hull will be the most important to consider when maneuvering.

In no wind conditions, the direction of the first breeze is better identified by a traditional wind vane than by the windex, which is more sensitive to rolling and pitching. Painting the ends with fluorescent paint is a trick to make them more visible even at night. There are also those who say that the noise of the weather vane made from old VHS tapes or aluminum tapes is an excellent deterrent for birds.


telltales quick guide


In this case, telltales indicate the correct incidence of the forward part of the sail with respect to the wind, mainly affected by the tension of the jib sheet.Let’s see some examples.

-A – telltales are parallel to each other: = OK, in that area, the headsail is trimmed, angle of attack and attack are correct, the flow is laminar in both upwind and leeward.

• B – The telltale is upwind, the sail is too much hauled, the wind generates a lot of heeling and little progression, it is necessary to ease the jib sheet.

• C – The windward telltale falls downwards = the sail is too slack, the sheet must be hauled.

 • D – Telltales in erratic position = non-laminar and turbulent flow, the sail angle is deeply wrong, the shape is not good, eddies are forming or the sail is already receiving turbulent flow such as a gennaker’s rejection or spi.


Leech: they indicate if the angle of incidence is correct, and if the overall outlet air flow is laminar. They must run parallel to the battens. They are adjusted starting from the uppermost one, acting mainly on the sheet.

Mid area: above and downwind, they provide information about sail fullness. Downwind, they also indicate the turbulent rejection of the overly fucked headsail.

Luff: They provide information on the flow at the angle of attack, reflects the effects of the cunnigham on dinghies and fast boats. On pivoting mast catamarans, they allow to adjust lift or indicate where you reach voluntary stall to reduce power.


On the spinnaker,they are useful in combination with wind indicators on the spinnaker pole, which must be perpendicular to the incoming wind. 

On the Gennaker, especially leeward, they indicate turbulence interactions generated by the jib that nullifies the lift of the gennaker in faster speeds.


Wind vane tapes for shrouds. These wind vane tapes for shrouds, sold in pairs, red and green, are made of nylon with velcro closure. They cost 13.45 euros. Find out more

Flag. Levante is a perfect option for small boats and superastructures. It is applied to the side of the mast, with a bayonet bracket. Balanced with counterweight, it has a price of 12.99 euros. Find out more

Digital telltales. Trimcontrol e-telltales are real electronic telltales that send data to the on-board instrumentation and even to an app on your mobile phone. Battery powered, they are installed on the sails like the classic ones, they send data to the control unit up to 4 times per second. The price is on request. Find out more

Article by Luigi Gallerani

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