Quantum Article on Spinnaker Trim

John writes:
Attached is a must-read Quantum article on Spinnaker (and Main) Trim.

While the entire article is worth reading ( and please do), here are some of the key points for Zamazaan:

Trim Lessons: Aerodynamic Mode [less than 145 degrees apparent wind angle]

In this aerodynamic mode, sheet trim is critical. Overtrimming drastically reduces the driving force and increases the side force and drag. The first rule taught to all spinnaker trimmers—ease continually until the luff curls —holds true. In the tunnel, the best driving force numbers were produced when the sail was eased so far that it began shaking violently just before it collapsed.

A spinnaker "flying on the edge" could easily produce 10- to 15-percent more driving force than the same sail overtrimmed.

If pole height was positioned on the low side of commonly accepted practice, the spinnaker luff became more stable, and hence the whole sail could be eased farther. A lower pole also pulled the shape forward and opened up the back of the sail. This more genoa-like shape reduced side force. Setting the pole 5 or 10 degrees aft of perpendicular to the wind also, as one would suspect, improved forward force. This confirms the advantage of keeping the pole 12 to 18 inches off the headstay on breezy, tight spinnaker reaches when you're trying to sail as high as possible.

Trim Lessons: Barn Door Mode [more than 145 degrees apparent wind angle]

By 145 degrees apparent wind angle, we are fully in the "barn door" mode.

At these angles, sheet trim became somewhat less important , while pole position was critical. The best driving force was always produced with the pole farther aft than dictated by the second rule of spinnaker trim—pole perpendicular to the apparent wind. The pole could be set 10 or even 20 degrees aft of square to the wind. This reinforced another tenet of modern spinnaker trim: projected area is the key on a broad reach or run—we want a bigger barn door! Squaring the pole stretches the foot tight, projects area, and gets the sail out from behind the mainsail.

Finally, don't forget the mainsail —the tunnel showed that if it was over- [too far in] or undertrimmed [too far out], it also had a devastating effect on total power .