The app will only show you races that you can start to track on that day.
Once you join the race the app starts to use the GPS to collect position data so it would be a huge battery drain to join the race hours or days beforehand. Best practice is to start the tracking when you go to the boat and start to rig.
You can upload a GPX file of your tracks to Sailchart once you have finished sailing, either on the same day via the Sailchart app or using the Sailchart Dashboard. However live tracking is only available if you use the app or dedicated GPS tracker.
This is only a requirement if you turn on the 'use heading and heel' when tracking. It then uses the phone to measure heading and angle of heel, so the phone must be level and pointing in the same direction as the bow, though doesn't have to be on the centre line. It must be level though, so vertical is not going to work. In testing we found that the phone could not accurately measure heel when vertical.
Once a race has finished, Sailchart needs to run an analysis routine to calculate the leg statistics. This is done when the race administrator defines the course sailed (sets the course marks and any waypoints), updates the actual start and finish times and sets the race status to 'Completed'.
When the race marks are defined by the race administrator, they need to ensure that they are positioned such that every boat's track actually rounds the mark. If the marks are set from preset club marks, the actual mark position for a specific race may differ to the preset position. The actual position can vary because of tidal effects and also GPS drift. However, occasionally the tracks for one boat are significantly offset from other boats, for example due to a GPS fix error in the tracks for that boat. It may not be possible to adjust the mark positions so that the rogue boat rounds the mark, in which case it's mark rounding time will be estimated based on when it was closest to the mark.
A leg is completed once a boat has passed a mark or waypoint, so whilst you can use either, it is best to use rounding marks rather than waypoints. When you define a mark rounding, you specify whether it is a port or starboard rounding (gate roundings are also supported), so Sailchart will only complete a leg for a boat that has sailed the correct way round a mark. If the race course requires a boat to round a mark, they are best defined as rounding marks not waypoints.
To use a preset course when defining a race, switch to the Course tab, press Copy… and a dialog allows you to either copy a preset course or a course from another race.