Sailing vessel having unknown crew from Hamburg (5)
I believe the answer is:
yacht
'sailing vessel' is the definition.
(I've seen this before)
'unknown crew from hamburg' is the wordplay.
'unknown' becomes 'y' (algebra).
'crew from hamburg' becomes 'acht' (I am not sure about this - if you are sure you should believe this answer much more).
'y'+'acht'='YACHT'
'having' acts as a link.
Can you help me to learn more?
(Other definitions for yacht that I've seen before include "Fast sailing vessel" , "Light sailing-vessel for sport" , "Sailboat" , "Pleasure craft" , "Sailing or motor vessel for cruising or racing" .)