Sensitive to pain in small boat (6)
I believe the answer is:
tender
This could be a double definition.
'sensitive' is the first definition.
('tender' can be a synonym of 'sensitive')
'pain in small boat' is the second definition.
'tender' can be an answer for 'boat' (tender is a kind of boat). I am unsure of the 'pain in small' bit.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for tender that I've seen before include "facility for steam train" , "Painful when touched" , "Bid - not toughened" , "Gentle, not tough" , "Rented (anag.)" .)