Hi Wouter,
I would never publish BS on this forum or any other forum. That is not what these forums are for. Also in my little narrow window of sailing knowledge and experience, there must be millions of details about sailboats and rig designs that I do not know about. I do not claim to be "all knowledgeable" like some people. I do know that when I put a spinnaker on my first RC27 in 1983, I saw immediately that some kind of an automatic jib jibing system would be of great benefit. Prior to this I used a wire bridle across the tramp with a double jib sheeting system.
The first thing I tried was to route the jib sheet to the jib tack and then back to the jib car and up to the jib clew. When the jib sheet was trimmed to set the jib leech and overall shape to the proper form, the jib car was immediately in front of the mast on boat centerline. Well, this obvisously won't work. One could always bend the jib track to the radius of the foot of the jib and add a second control line to the car but that wasn't good enough for me. I wanted it to be automatic, jib car position and sail shape controlled by one line. For this objective to work, the tension in the jib sheet had to be reduced to let the car/sail run off center with sail pressure without losing control of sail and leech shape. When the sheet tension was eased and the jib car began to run off center, the sail became too full for sailing to windward and the luff had backwind in it. The question became, "how do we have a high level of tension in the jib sheet for proper sail trim/shape and a low level of tension in the sheet at the same time to allow wind pressure push the jib car and sail off center for sailing to windward and reaching?" This objective was acheived by adding mechanical advantage between the jib car and jib clew. Pulley systems from 2:1 to 6:1 were tried. On the RC27 sail plan that I was working with at the time, I found that a 4:1 mechanical advantage pulley system did the trick. I could set the sail shape/leech tension that I had in the first place with only 1/4th the sheet tension in my hand or with only 1/4th the sheet tension in the sheet leg from the jib car to the jib tack. Now the wind pressure in the sail allowed the jib car to find an equilibrium point off center at the proper angle for sailing to windward with the same tension in the sheet that properly trimmed the sail. The trick was that the sheet tension was multiplied by 4 only between the car and jib clew. When the sheet was eased, the car moved out and the sail became fuller and if the sheet was tightened the car came in and the sail became flatter. I also learned that a batten connecting the jib luff to the clew corner of the jib made the car run slightly further outboard and it kept the jib from becoming too full as the sheet was eased for reaching. This batten acted something like a bendy boom. (And by the way Wouter, some Tornado sailors do let the jib car control line out for reaching. That is why the jib tracks are more than 18 inches long. The crew does have to come to the center of the tramp to uncleat and let out this control line. They also have to come back to the center of the tramp to tighten this car control line for sailing back to windward.)
I want to point out that ARC products have both straight jib tracks and curved jib tracks for various reasons. I happen to like the straight track system better myself on the 27 and 30.
Another comment for Wouter: Wouter, I have been going to international boat shows since about 1970. I have looked over hundreds of sailboats of all sizes and shapes. Most of these boats were "cruiseing boats". I have never seen one of these boats rigged with a self tacking jib system. Cruiseing boats do not give a hoot about racing/rating rules. These boats/rigs are designed to be "simple and easy to sail". Rules do not matter! I will make a prediction: Within the next 5 years you will begin seeing cruiseing boats rigged with self tacking jib systems like beach cats have today.
Bill
PS Wouter, there are self tacking jib systems pictured in Harken's catalogue. You will never see one of these arrangements on a boat because they do not work worth a hoot. The beach cat system, straight track, works very well and is very simple to work with one control line.