How to Trim the Jib Using Telltales

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How Telltales Work

Red and Green Telltales on a sail

 Tom Lochhaas

On most sailboats, telltales are positioned on both sides of the leading edge of the jib (called the luff). These small strips of yarn or ribbon show how the air is flowing past the luff and can indicate when you need to trim the sail.

At the best sail trim, air flows smoothly past the luff on both sides of the sail. The telltales then stream back horizontally on both sides of the sail, as you can see in this photo. The red telltale is on the near side of the jib (to port), and the two green telltales are showing through from the other side of the sail (starboard).

This sail is in good trim because the telltales on both sides are streaming straight back. With good air flow on both sides, the sail’s shape generates power.

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When the Telltales Flutter

Jib Telltales Fluttering on a sale

Tom Lochhaas 

Here the jib is out of trim. Notice how in this photo, the green telltales are hanging down limply instead of streaming back horizontally. This shows that the sail is out of trim.

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Close-Up of Fluttering Telltales

Closeup of Fluttering Jib Telltales
Tom Lochhaas

Here’s a close-up view of telltales on a sail not in good trim. The telltales may hang limply or flutter up and down.

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Trim the Sail to Stop Telltale Fluttering

Jib Telltales Fluttering on an expanding sail

 Tom Lochhaas

It’s simple to trim the jib when the telltales show a problem. Move the sail in the direction of the fluttering telltales. If the fluttering telltales are on the inside of the sail, as shown in this photo, then pull the jib in tighter until they are streaming back horizontally.

If the fluttering telltales are on the outside of the sail, then let the jib out until they are streaming back horizontally.

Depending on the sunlight on the sail, it may be difficult to see the telltales on both sides of the sail at the same time. You may have to change your angle of vision to catch their shadows. With a little effort you can usually see the telltales on both sides.

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A Well-Trimmed Jib

A well-Trimmed jib on a sail
Tom Lochhaas

This photo shows the jib in good shape for the boat’s angle to the wind. The telltales are streaming straight back on both sides of the jib.

This is your goal when trimming the jib—and will give your boat its greatest speed.

(Here the mainsail is stowed on the boom beneath its cover to make it easier to see the shape of the jib.)

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Jib Telltales When Running

running jibs on a sail
Tom Lochhaas

The jib can be trimmed using the telltales and most points of sail—but not when running downwind. When the boat is moving close to directly downwind, the wind is pushing the sail rather than flowing by it evenly on both sides.

The telltales then become useless for sail trimming and may hang limply, as in this photo, or flutter.

When sailing downwind, you have to trim the jib more by its overall appearance and how it reacts with movements of the boat. Your goal is to keep the sail full and drawing. Otherwise, as the boat rolls side to side on waves, as commonly happens when sailing downwind, the jib will repeatedly collapse.