Clue: Pipes captain aboard whilst blockading harbour (7)
Answer: HOOKAHS
Explanation: Definition: Pipes

(Captain) **HOOK** (a ship's captain, so "aboard") + **AS** ("whilst") *blockading* **H** (harbour)
 

 
*I've not come across "h" for "harbour" before, but as I am on a short break, I have no access to a paper dictionary and can't confirm. It's not in the Chambers app, and it's not an Ordnance Survey abbreviation…