TLDR*: Press MODE and MAX simultaneously to display Line Square To in degrees magnetic on the new ProStart.
Did you know the new ProStart automatically calculates the magnetic bearing the starting line is square to?
It does! To display ‘Line Square To’ bearing, press the MODE and MAX buttons at the same time. If you knew this, that's great! Thanks for reading the ProStart manual or the entirety of the last blog post.
If you didn’t know this, that's OK too. You're in good company. The results of an informal poll of top sailors at the 2022 Bacardi Cup puts you in the majority.
"Oh, that's awesome! Super helpful feature. Don't tell anyone else about it." - Anonymous tactician. Multiple World Champion and Rolex Yachtsman of the Year.
The new ProStart, running firmware version 35, automatically calculates the magnetic bearing the starting line is square to. This allows you to easily compare the line square to bearing to a head-to-wind bearing on your compass. Do this every start and you'll save your self the hassle of running the line and mental math.
To display ‘Line Square To’ bearing, press the MODE and MAX buttons at the same time.
‘Line Square To’ is calculated as the magnetic bearing from the right end of the line to the left end of the line plus 90°:
On a course with the first mark to windward, ‘Line Square To’ is a tactical aid which gives you information about which end of the line is favored. Shoot head to wind, check the bearing on a magnetic compass and compare this measurement with ‘Line Square To.’
The right end of the line is favored when the Wind Direction is to the right of ‘Line Square To.’
The left end of the line is favored when Wind Direction is to the left of ‘Line Square To.’
How much does ‘Line Square To’ matter? Ten degrees of line bias favors one end over the other by approximately 20% of the length of the line. Often starting lines are 1 to 1.5 times the sum of the length of the fleet. In a 20 boat fleet that equates to 4 to 6 boat lengths of advantage!
*TLDR = Too long. Didn't read.