We have seen how to trim the main for power, and to balance the helm. The main causes a lift for the headsail due to upwash, so the genoa can be sheeted further outboard. Since the lifting forces act in the perpendicular to the chord, the lift forces are more forward in direction. The headsail is also the leading edge of the sailplan – there are no stays, halyards or mast to get in the way.
There are fewer controls available to allow us to shape the sail – the halyard, the backstay and the sheet. So the shape in the headsail is built in to it, and has to be changed to give different characteristics. However there are some tricks that can be used to extend the range of the headsail you have up.
Twist is once again where we must start, as it also sets up the mainsail also. Use the telltales to determine whether or not the twist is OK.
Too much twist – top windward telltales will not fly.
Too little twist – the bottom leeward telltale will not fly.
Move the sheet car forward if there is too much twist, and aft if not enough. When they break evenly, the twist is correct.
However there are times when you can break this rule – when overpowered, you can take the car aft, over-twist the sail, and spill some wind from the top of the sail. This also flattens the bottom of the sail, which is better in these higher winds. And taking the car forward gives you more power if you need it.