A hundred in hasty change for the boats (6)
I believe the answer is:
yachts
'boats' is the definition.
(yachting is a kind of boating)
'a hundred in hasty change' is the wordplay.
'a hundred' becomes 'C' (Roman numeral).
'in' is an insertion indicator.
'change' indicates anagramming the letters.
'hasty' with letters rearranged gives 'yahts'.
'c' placed into 'yahts' is 'YACHTS'.
'for the' acts as a link.
(Other definitions for yachts that I've seen before include "Act shy (anag)" , "Pleasure craft" , "Racing or cruising boats" , "Vessels for cruises?" , "Pleasue boats" .)