Eric,

What you describe is exactly the way you would go when ordering a F16 package for a Taipan 4.9.

The F16 main is slightly larger but, more importantly, has a larger squaretop. The jib is reduced in size by some 12 % but gets a larger luff length as higher aspect ratio. At the same time one moves the jibsheet to the (far) front of the trampoline where the out of the way. In the old days this required the fitting of barberhaulers to pull the crew to the proper sheeting point for downwinf sailing but with the introduction of the gennaker the sheeting points don't move about that much any more. Ergo, you can get away with less distance between blocks and clew.

I questions a few sailmakers about the non ovelapping jib and several indicated that airflow theory has changed a bit. It seems that it is not the jib which is important with respect to the airflow over the mian but rather the other way around. The main is important in determining the airflow over the jib. Ofcourse for the last ; having an overalp is far less important as it becomes a suction situation instead of a slot / ventury situation. It seems that a NASA aerodynamisist whose name I can't remember now has proven that the old theory of the slot ventury was incorrect and he did that back in the 60's.

And the theory is more detailed than I want to write down in this reply.

However this "new' theory is confirmed by experiments in "High Performance Sailing" by Julian Bethwaite and he even shows some wind tunnel pictures of it.

Now, ofcourse a bigger jib will always produce more power but it seems that overlap is more linked to having more power because one can than fit a bigger jib than that the overlap itself is the cause of more power.

With respect to powering up a sloop rig in respect to a uni rig. It is found that the power increase is more than can just be accounted for by the extra area. In sailboat sailing that is ofcourse. Landyachts behave differently because, well, they go 2 to 3 times as fast as catamarans. So what is the reason why more power is developped ? One reason it that a sloop rig can skew the airflow (wind) over a larger angle than a uni rig can. This is especially productive on reaches and shy reaches. In the old days also when going on broad reaches and downwind but we mostly have the gennaker for those courses now. But even upwind it seems to work. Just like with the flyer A-cat catamarans are increasingly found to be better footed off than pointing high. The Flyer was found to be faster to A by pointing slightly lower and moving faster than by pointing high and moving less fast. Same comments are heard over and over again with respect to the Taipan 4.9.

The cat rigged Taipan sailors typically move their traveller about 4 to 5 inches from the centre. The comment is that with the mainsheet centred the boat just doesn't seem to drive as well. By placing the jib in front of the main and centre sheeting the main the whole rig can now fully bend off the airflow to the centreline when going upwind and be more efficient is harvesting energy than the extra area of the jib alone can account for. The cat rigged mainsail alone can not bend off the airflow to such a large angle on its own. Ofcourse this aspect is not influenced by having an overlap or not. You will have this effect by having a jib or not and not by having an overlapping jib or not.

Than we have the extra effect of have a slot between the jib and main. But this is a different effect than the overlapping slot effect we just discussed. In general an airfoil wing devide in to parts with one in front and one behind the other in more efficient than the same area in one undevided airfoil.

In leemans terms the decellerated airflow near the surface of the jib is preventing from continuing near the surface of the mainsail and detaching there by a flow of fresh and undecellerated air coming from the slot between the jib and mast. This fresh boundery layer is instrumental in assuring attached flow over the mainsail resulting in good power. Or at leadt more than would be the case when the area placed in the jib would simply be have added to the mainsail.

Several people are often quickly to refer to the cat-rigged C-class catamarans but often overlook the fact that in that class teh slotted sails are by long the prefered rig. This slotting of the rig is also at work between the jib and main although less effeciently due to the triangular shape of the jib and the fact that it only properly interacts with the lower halve halve of the mainsail instead of the whole mainsail. Ofcourse by slotting the whole mainsail as done in the C-class the principle of slot effect is far more optimized than would be with a jib and mainsail configuration, however it is still the same process at work albeit to a different magnitude.

All this can be researched and discovered by anyone making an effort in rig designing and has been know for some time. Although I must admit that it something is more beneficial to leave several people in the dark about these issues. But that time has ended.

So the main conclusion from this reply is that :

Two of the main processes at work that result in more power being produced are unrelated to having an jib with an overlap. -1- bending off airflow over a bigger angle and -2- Slot efect which replaces used up boundary layer by a new fresh and high on energy boundery layer.

1 proces directly linked to power production by the jib is linked to having an overlap and that is the total amount of jib area. However this can be counteracted by using the bridle strut and adding the removed area below the current jib. With respect to teh F16 rules some of the Taipan 4.9 jib can be moved to the mainsail and be used to make the larger squaretop. All this while clearing up the trampoline.

Goodall Yacht sails have expressed that they will supply a Taipan 4.9 with a fully optimized Formula 16 rig when requested. This may include a selftacker.

With kind regards,

Wouter