| Jib with telltails and leechtails |
The sail work as a wing. If there is one sail, it is pretty easy to imagine. Air flows over the sail and creates a pressure difference that pulls the boat forward. It's just like the wing on a plane, except the plane is pulled upwards. However, the pressure will not pull the boat forward in the sailing direction. That's where the keel comes into play. More on that in a later post.
Telltails show the airflow coming on to the sail. Leechtails show the air coming off the sail. If there are two sails, they work almost as a single wing. The main being a sort of trimflap for the jib. When there's a jib and a main, the end of the wing is effectively the leech of the main, so that's where the leechtails go;
Telltails show the airflow coming on to the sail. Leechtails show the air coming off the sail. If there are two sails, they work almost as a single wing. The main being a sort of trimflap for the jib. When there's a jib and a main, the end of the wing is effectively the leech of the main, so that's where the leechtails go;
| Main with leechtails |
The leech tails are important too, but not for the steering. Leechtails are more of a tool for the trimmer. The leechtails should point aft as if the sail continued some 10 inches in that direction. If they bend to the backside of the sail, the sail is stalling and the leech is too tight. If they flutter, the leech is too loose, and that's pretty much all you need to know in order to trim your sails and sail max speed. When the basic trim is in place, the leechtails take over and become the most important second by second "device" for the trimmer to make sure the boat is well balanced and runs at maximum speed. The helmsman stays with the telltails.
This is ofcourse a very short version of the truth. Of course there are other factors such as the fullness of the sails, the leech tension, the twist, halyard tension, headstay tension and what nuts. These trimfunctions are mostly about adjusting the sailshape to the current windstrength. Now, it should be pretty obvious why telltails are key to a good sail simulator. That's why we love the Flying Fizz. It not only behaves pretty much like a boat, it also has those telltails working almost like real ones.
Thanx to Mikko from WB sails for letting me use these pictures. Go there and read more great articles about saildesign.



















































