They establish what a ship does when it sinks (8)
I believe the answer is:
founders
'sinks' is the definition.
(foundering is a kind of sinking)
'they establish what a ship does when it' is the wordplay.
I cannot quite see how this works, but
'establish' could be 'found' (found can mean to set up or establish) and 'found' is found within the answer.
'when' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for founders that I've seen before include "Goes to the bottom" , "beginners" .)