I was about to post this same question. Has anyone found a place that truly works well? In any other boat I use telltales, but in the sunfish they seem to never fly quite true. I am currently not using telltales, but I think if I found the right location it would significantly improve my beat. I've used mast head and eye level wind indicators too, but they really only seem to help off the wind in light air.
In previous posts it was said that these locations work well
"place the first set at the top of the third (middle) panel, approximately 30" from the gaff. The second set of two should be attached to the sail at the bottom of the second panel (the panel with the class insignia), approximately 26" from the gaff."
It seems, however, that everyone has their own preferences and everyone's telltales are in different locations. Generally telltales are placed in the deepest part of the sail. This means that for the sunfish two locations are needed simply because the asymmetric nature of the sail.
Interestingly I noted the location of Jonathan's (the 2009 NA champ) telltales this week. His are the only ones I have ever seen forward of the mast. His first was slightly forward of the mast and his second was just aft of the mast and about a foot higher up.
Has anyone found a definitive location with which they are satisfied and which works on both tacks.
I have a couple of 10" long 12 ga. +/- wires zip-tied to the upper spar about 4' above the deck, each with a yarn tied to the end. with the sail centered over the boat, they stick out 45 degrees each side of centerline. They show me the wind direction just forward of the leading edge of the sail. I'm not saying telltales on the sail aren't good, but I like these.
The problem with telltales on a Sunfish is that the mast causes turbulence on starboard tack and on port tack the mast pushes into the main creating a terrible shape. Despite that it is helpful to place telltales sufficiently aft of the mast that they are in somewhat undisturbed airflow. Putting a couple on the leech isn't going to hurt either. I find on starboard tack that both telltales work fairly well, on port tack I usually go by the leeward telltale. Wind indicators that are mounted on spars or anyplace other than the sail will not tell you whether you have good airflow over your sail, they will only tell you the apparent wind direction.
I'm not near my SF at the moment but I recall they are 3 to 4 feet above the horizontal boom and a couple of feet aft of the upper boom. The SF manual should have some info. It wouldn't hurt to place one at mid leech, since the boat isn't rigged to control twist in the main, there isn't much point putting telltales on the upper and lower leech. Just don't put them too close to the mast or upper boom as there is too much turbulence to yield worthwhile readings.
Here's a great photo from the 2009 Sunfish North Americas illustrating the sail shape from a perspective sailors don't often get of their own boat. I've marked the "zone" Zeppo describes and it's where I put my telltails as well. I seem to experiment along that line and usually end up with a third, lower one, though port tack messes with it.
Thanks Rick et al for that link and all the great photos of the race. Some fantastic examples of how to rig can be found among the shots.