Tiller in shelter onboard essentially destroyed (4)
I believe the answer is:
cain
'tiller' is the definition.
(Cain tilled the ground in the Bible)
'shelter onboard essentially destroyed' is the wordplay.
'shelter onboard' becomes 'cabin' (cabin on a ship).
'essentially destroyed' suggests removing the centre (the essence of the word is removed).
'cabin' with its middle taken out is 'CAIN'.
'in' acts as a link.
(Other definitions for cain that I've seen before include "Eldest son of Adam, Eve" , "First son" , "Brother of Abel" , "Abel's brother" , "Adam's son" .)