Boats, vehicles and guides stop you selling more than you can run. Every option that uses one shares its count, so a time stops selling once all of them are booked.
Open the product from On sale and scroll past the options to Boats, vehicles and guides.
Press Add one. Type a Name, choose the Kind, and set How many you have.
Type the minutes it needs between two bookings in Turnaround, then press Add.
A new one is marked Will be added. Press Save so options can use it.
Under each option's uses line, press Add and keep one per booking. Use per ticket for something each traveller uses.
In Changes to save, check the list and press Save all.
Tip. A booking holds the van for its whole trip plus the turnaround. When every van is booked for a time, that time stops selling until one is free.