My Marine Trader 38' was USA registered and named Nylander when I bought her.
I'm happy to report they she is now UK registered and named Hermione (officially) and with that the old US flag was today withdrawn from service...
... and my nice (oh, so many coats of varnish) restored flag pole is now flying scarlet upon stern :)
The Red Ensign (or scarlet) is the flag flown to designate a British ship (in this case, the red background denoted that it is a civilian vessel).
A big day for little Britain ;)
Tom Calthrop, Hatton Garden, Dominica