Is she Arrow of Norwich?
In 'Their Own Story', Peter Duck appears as a hired wherryman who seems to come with the hired ship, and he could well be the owner. Since in this early manuscript Arthur Ransome flips between the names Gibber and Jacko for Roger's monkey, he might well have conceived Polly Ann as Mr Duck's "day job" ship, called Arrow of Norwich in the final published Peter Duck.
Is she Sir Garnet?
Polly Ann has another possible alter ego, although it is stretching a point: Sir Garnet, only in the sense that Sir Garnet's mate is Simon Fastgate, who, like Mr Duck, was modelled on Carl Sehmel, the Ancient Mariner (Life page 257,336)