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When we got our boat from the factory, we had ordered it with a square-top mainsail.
The “standard” sail in a pinhead sail, which is shaped like a triangle.
A square-top sail is a trapezoid shape. The foot is wide and has a 90-degree angle on the front corner. The head is flat and parallel to the foot.
This shape dramatically increases the size of your mainsail. While it is heavier, it makes up for it in improved performance.
The downside to a square-top mainsail is that the rigging gets more complicated.
When we purchased our boat, Fountaine Pajot was not offering the option to rig an automatic square-top mainsail. However, Lagoon, manufactured not far from La Rochelle, was.
The sails were being made by Incidence, so while in La Rochelle we had them come pick up our sail to fit the automatic rig.
Normally, you have to detach the halyard (line that pulls the mainsail up) from the head of the sail in order to get the sail to go all the way down. Incidence rigs a system that allows the head of the sail to pull away from the mast while it is being lowered, without detaching anything. Incidences took the mainsail off Starry Horizons and installed it back on the same day!
The tackle line (B) is made out of Dyneema, and when in Grenada (after a year and a half of sailing) I used Dyneema to splice my own replacement for the tackle line. When splicing this line, you don’t have to be exact because of the lashing (D).
A really technical article on square top v pinhead from Saphire.