With ample space to tie up at the end of the jetty (5)
I believe the answer is:
roomy
'with ample space' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for roomy that I've seen before include "Having big space" , "Commodious" , "Having plenty of space" , "Spaced-out" , "Extensive" .)