Jim K. - Hats off to you for your Footy spirit of inventiveness!
Or re-inventiveness in this case as I saw this particular one on several A Class jibs in the seventies. The A Class measures the fore-triangle area (the triangular area bounded by the mast, jib stay extension to the deck, and the distance from that extension back to the mast). Split sail jibs fit into this area just like regular ones but open up downwind to form sort of a spinnaker. The drawbacks were that the split jib did not have a very good shape going upwind and when the sail got wet the two halves wouldn’t separate.
History aside, why would it be desirable on a Footy to double the sail area downwind?
Well you made me think about this for awhile, and hopefully I will try to explain my thoughts on this. most footys love to submarine on the down wind leg and yes you can sail faster just off the wind but that requires several tacks and more area to cover. if you could get the hull up on a plane downwind while everyone else in the fleet is tacking , I think the results would be advantageous.with the aft mast ,the rake of the sail causes lift as well as forward thrust, so why not promote that even more with extra sail area. this would be helpful so long as it did not interfere with the sail performance at other points of sail. If you were to look at the head of the sail leaned well over towards the wind , you have in effect a second dimension foil from head to foot, this would depend on the angle, but it would be better than a conventional sail rig that acts as a wall and only wind speed and a whole lot of drag are the factors for forward motion.
Hi Jim - Try your rig and see. I am pretty sure that you will find that your footy still dives. It is the simple mechanics of an over canvassed really short boat.
Here are my predictions; in light wind the rig won’t go out so the boat will miss a lot of puffs. To fix this the rig will need a counterweight forward of the pivot so that it will naturally want to go out when the sheet is eased. Once out, if the wind dies the sail will droop showing negative camber. This is also slower to react to puffs on a calm day because the sail has to lift to fill. If there is wind then you do have a lower center of effort, but as I mentioned above, the sail is not optimized for upwind sailing. Upwind sailing constitutes the majority of distance in a triangular course because of tacking. Upwind is also the first leg after the start and winning that first leg (particularly on a short course) puts you in a controlling position over the fleet. Sacrificing upwind ability to prevent diving (even if this rig effectively solves the problem) is still not a winning strategy. Case in point is the M Class design Scalpel. This boat is only of average speed off the wind but is optimized for pointing. It now dominates the M Class and its high price tag has forced a lot of people out of the class.
I wish you luck with this rig in spite of my reservations. Something new like this does require some time to work out the bugs so stick with it for a while before hopping to the next project. I am sure you will learn from the experimenting, I always do. Share your insights and conclusions with us here.
What’s the final configuration for the Wiebel rig? Could you please draw up a graphical thing for us? It’s tough to put togeth the design from the photos.
Sorry for the delay ,it has been some time since the last visit. I have scratched down a quick drawing of this rig as it stands today and I am still testing when time allows.the biggest problem to overcome is the sheet control as it must allow the hike bar to function properly and requires a great deal of travel to present sail in downwind conditions . the counterweight can be removed and sailed well in light air and currently using a single sail configuration.
If you draw a free body diagram (Physics 101) of the forces acting on the hull and sail in the pitch axis, you will see that there is very little benefit without moving the rig very far forward.
A scheme of this sort will actually work to reduce submarining, using a very long bowsprit (about as long as the hull). In some other threads, I had done some testing in that regard. But moving the rig that far forward unbalances the whole system, so it is necessary to do something unusual to restore balance in the yaw axis. I had proposed mounting the keel at the prow to restore balance, and had built a free-sailing foam hull as a test vehicle. But this would probably cause a strange dynamic response, which has not been tested. Another possible balancing mechanism would be a mizzensail, on a transom-mounted mast, with a bumpkin.
Of course, as Neill has said, it is necessary to accomplish all this without impairing the windward ability of the boat.
NOTE: Please accept my apologies for repetitiveness. I just realized that I sent a similar response to this thread several months ago.
Keep it coming along… I am loving this thread!! (fades back to admin duties)