Telltales simple devices made out of nylon, wool yarn, cassette tape, etc. and attached to a sail (jib or main) by adhesive locator discs or pulled through the sail with a proper needle and knotted to stay in place. This wonderful little tool is both low cast and very effective if you position it properly and understand how to read them. The following should help you to do both, The end result should make you and your boat better sailors and increase your level of fun!
Start with the headsail
Let's look at the headsail first since it's trimmed first. Telltales should be positioned 8" to 12" back from the luff. I usually use my wrist to my elbow and by dividing the luff into three quarters you will put on three sets, port and starboard, one set each at the quarter, half, and three-quarter mark of the sail (refer to the diagram).
You might have to move the location up or down a bit to avoid a seam, which can cause the telltale to hang up. I prefer adhesive-backed locator discs made out of insignia sloth. These seem to work well, come in a variety of colors, and allow you to position the port and starboard telltales at different levels which will let you see both telltales, since during daylight hours the shadow of the one on the back side will usually show through. If you have acetate trim windows you will have a great view of both telltales.
When sailing close hauled or close reaching, trim the jib until it just stops luffing. Notice the telltale on the windward side. When it stops fluttering and lays smoothly against the sail you are in trim. Check the telltale on the leeward side, it should also be streaming aft, lying still and be parallel to the windward telltale.
At this point, check all telltales top to bottom, If they are all performing the same the headsail is sheeted in properly and you are "in the groove". If the top one is fluttering move the sheeting block forward a bit. If the bottom telltale is fluttering move the block aft.
Once the sheeting angle is correct and the sail is trimmed properly, you can use the telltales to drive the boat. Since they are lighter than sail cloth they will tell you when there is a change in the wind and give you a chance to adjust the helm before luffing the sail.
Heading up should cause the windward telltale to break first, flying upward. When falling off the leeward ones will break and begin to flutter. The more you work with them the better you will become at reading the information they give you.
