I found this to be a fascinating bit of reading
In Grand Prix classes throughout the sport of sailing, it is well known that sheeting angles are becoming tighter and tighter – modern TP52s have jib sheeting angles as close as 4 degrees off the centreline. The J109 class in Ireland is a growing and competitive fleet so we felt it necessary to take a fresh look at the sail plan and systems aboard the now nearly fifteen-year-old design with an aim to improving performance.
The J109 have evolved significantly over the past fourteen years. The most visible change has been the shift to a non-overlapping jib setup for optimum IRC performance. This shift in sailplan has a significant effect on the boat’s light air performance due the headsail area reduction.
To compensate for this reduction in power the class uses an inhauling system – this narrows the slot between the mainsail and headsail, in turn increasing the power of the entire sail plan. Up until now the common inhaul point has been the edge of the coach roof – approximately 9° sheeting angle. This is effective in true wind speeds of 15 knots and above – but below this the boat is still relatively starved for power when compared to their genoa flying predecessors – we believe further performance is attainable.
During the winter of 2018 UK Sailmakers Ireland, in conjunction with Pat Considine of UK Sailmakers Chicago, carried out a Fluid-Structure Interaction (FSI) test cycle to determine the effectiveness of jib inhauling to a sheeting angle of 6 degrees - just inside the halyard turning blocks on a standard J109.. . .
The rest of the article is at https://afloat.ie/.../41151-uk-sailmakers-j109-class-fsi-test-report
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