Ferries

Is it necessary to book ahead for the ferry Gran Canaria to Tenerife, or just turn up at the harbour? 2 Persons with bicycles, during christmas holidays. 

Foro de bicis en Tenerife. Cycling Forum in Tenerife, Canary islands.
https://www.tenerife-training.net/Forum/
https://www.tenerife-training.net/Forum/viewtopic.php?f=13&t=555