Henry measures the sail ropes (8)
I believe the answer is:
halyards
'the sail ropes' is the definition.
'halyards' can be an answer for 'ropes' (halyard is a kind of rope). I am not sure about the 'the sail' bit.
'henry measures' is the wordplay.
'henry' becomes 'hal'.
'measures' becomes 'yards' (yard is a kind of measure).
'hal'+'yards'='HALYARDS'
Can you help me to learn more?
(Other definitions for halyards that I've seen before include "Nautical ropes" , "Ropes for raising and lowering sails or flags" .)