American banker in vessel with old raincoat on (7)
I believe the answer is:
potomac
'american banker' is the definition.
(American river - something with banks)
'vessel with old raincoat on' is the wordplay.
'vessel' becomes 'pot' (type of container).
'with' says to put letters next to each other.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'raincoat' becomes 'mac' (mac is a kind of raincoat).
'on' says to put letters next to each other.
'pot'+'o'+'mac'='POTOMAC'
'in' is the link.
(Other definitions for potomac that I've seen before include "Flower" , "Washington's river" , "River of Washington DC" , "Capital outflow" , "to which banks in Washington have access" .)