Claret and fortified wine on board ship - they're deadly (5,6)

'deadly' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'claret and fortified wine on board ship' is the wordplay.
'claret' becomes 'blood' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' is a charade indicator (letters next to each other).
'fortified wine' becomes 'port' (port is a kind of fortified wine).
'on board' is an insertion indicator (inserted letters are taken on board).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'port' placed inside 'ss' is 'sports'.
'blood'+'sports'='BLOOD SPORTS'

'they're' acts as a link.

Can you help me to learn more?