What is a “Square Starting Line”
In Sailboat Racing A square starting line refers to the line’s position relative to the wind. In the illustration above we show the start line and the first, windward mark. The Compass Rose indicates that the wind is blowing directly from the north (0 deg) to the south and the line is perfectly perpendicular with that.
If the windward mark is set directly upwind from the center of the line, then there is no geometric advantage to starting at the boat end or the pin end of the line. In this illustration the green boat starting at position 1 reaches the layline first and tacks but the blue boat then reaches the same point on the layline at about the same time.
There is a rules advantage to starting closer to the boat end of the line starting on a starboard tack. That puts you in a controlling position over the rest of the fleet. It also puts you on starboard tack when the green boat tacks and meets blue boat, whether that is on the layline or not.