Outline plan hasn't succeeded — it floats away? (5)
I believe the answer is:
ketch
'it floats away?' is the definition.
(type of sailing vessel)
'outline plan hasn't succeeded' is the wordplay.
'outline plan' becomes 'sketch' (a sketch is a rough plan).
'hasn't' indicates named letters should be taken away.
'succeeded' becomes 's' (genealogical abbreviation).
'sketch' with 's' taken away is 'KETCH'.
(Other definitions for ketch that I've seen before include "2-masted boat" , "The craft" , "Small sailing vessel with two masts" , "Jack" , "Two-masted sailing ship" .)