Vessel the companion had boarded earlier (8)
I believe the answer is:
schooner
'vessel' is the definition.
(type of ship)
'companion had boarded earlier' is the wordplay.
I cannot really understand how this works, but
'companion' could be 'ch' (Companion of Honour) and 'ch' is found in the answer.
'earlier' could be 'sooner' (synonyms) and 'sooner' is found within the remaining letters.
No letters remain.
This explanation may well be incorrect...
'the' acts as a link.
Can you help me to learn more?
(Other definitions for schooner that I've seen before include "Two-master; a glass" , "In the main it is" , "Swift sailing vessel - sherry glass" , "Item used for drinking" , "Old sailing ship and tall sherry glass" .)