Try getting 500 aboard vessel before last of tide (5)
I believe the answer is:
judge
'try' is the definition.
('judge' can be a synonym of 'try')
'500 aboard vessel before last of tide' is the wordplay.
'500' becomes 'd' ('d' can be a synonym of '500').
'aboard' indicates putting letters inside.
'vessel' becomes 'jug' (jug is a kind of vessel**).
'before' says to put letters next to each other.
'last of' suggests the final letters.
The last letter of 'tide' is 'e'.
'd' going into 'jug' is 'judg'.
'judg'+'e'='JUDGE'
'getting' acts as a link.
(Other definitions for judge that I've seen before include "Arbitrate" , "Deem; arbiter" , "Reckon" , "Estimate" , "rule" .)