A YachtBot race is a training session, race or some other event you're interested in tracking. Races have a start and end time, one or more yachts and optionally multiple buoys and wind units. You can either set up a live race before you go out to sail, or set it up when you come back.
Importantly, data collection is very different and independent from the setting up of a race on YachtBot. Our servers save data sent by any registered device and we keep all data for at least two years. A YachtBot race is merely a way to look at the data. Deleting a race does not delete, or in any way affect, the data displayed in it.
The time between when a device is powered on, connects and sends data, and is then powered off we sometimes call a session. Sessions don't overlap, by definition.