Crusader emblem in sweet old ship rounding cape (7,5)
I believe the answer is:
maltese cross
'crusader emblem' is the definition.
(symbol of English knights during the Crusades)
'sweet old ship rounding cape' is the wordplay.
'sweet' becomes 'malteser' (Maltesers is a brand of chocolate sweets).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'rounding' indicates putting letters inside (some letters go round others).
'cape' becomes 'c' (abbreviation used on maps).
'malteser'+'o'+'ss'='malteseross'
'malteseross' placed around 'c' is 'MALTESE CROSS'.
'in' is the link.
(Other definitions for maltese cross that I've seen before include "Symbol of the Knights Hospitallers" , "St John Ambulance emblem" , "Eight-pointed figure" , "Valletta symbol?" , "Most careless (anag.)" .)