At sea, I'll float fleet (8)
I believe the answer is:
flotilla
'fleet' is the definition.
(I've seen this before)
'at sea i'll float' is the wordplay.
'at sea' indicates anagramming the letters.
'ill'+'float'='illfloat'
'illfloat' is an anagram of 'FLOTILLA'.
(Other definitions for flotilla that I've seen before include "set of boats" , "set of vessels" , "many boats" , "Fleet of small warships" , "Fleet of small craft" .)