Calm down, there's a boat on the way (6)
I believe the answer is:
subdue
'calm down' is the definition.
(thesaurus)
'a boat on the way' is the wordplay.
'a boat' becomes 'sub' (I've seen this before).
'on the way' becomes 'due' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'sub'+'due'='SUBDUE'
'there's' is the link.
Can you help me to learn more?
(Other definitions for subdue that I've seen before include "Bring under control, tame" , "Overcome, suppress" , "Conquer" , "'Quieten, bring under control (6)'" , "Vanquish" .)