If your organization allows athletes to checkout equipment for private use, you may need to pre-reserve boats for practices to ensure that it is available. Boats can be reserved by going to Practices -> Manage and clicking on the Reserve Equipment button after selecting the practice. This will create an equipment reservation with the selected boats to make sure no other athletes reserve the boat during your practice time.
If you don't want to pre-reserve boats, you don't have to. All boats will still be available in the lineup builder so long as the boat is not reserved for a private reservation.