Dolphin’s mostly well out around slipway perhaps (7)
I believe the answer is:
grampus
'dolphin's' is the definition.
(grampus is a kind of dolphin)
'around slipway perhaps' is the wordplay.
'around' means one lot of letters goes inside another.
'slipway' becomes 'ramp' (a slipway is a ramp by water).
'perhaps' becomes 'gus' (I can't justify this - if you can you should believe this answer much more).
'ramp' going within 'gus' is 'GRAMPUS'.
'mostly well out' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for grampus that I've seen before include "Popular name for a killer whale" , "One often spouting" , "Good synchronised swimmer" , "Dolphin - killer whale" , "danger in the main" .)