Thank you John. At least Messrs Walton & Grimm had realised that some gloss on the term should be offered, even if only speculative.

If it did mean 'jib-boom', to be jumped on, then later versions, in which she [the ship?] had become 'a popular {or a proper} juberju', there was presumably some confusion of the wording of the original, & the term, confused or conflated with some term of approval like 'jubilee' or 'jube-jube', had become some expression of praise for the excellence of the vessel?

Speculative: but more than simply a 'whack fol the daddy' or whatever equivalent?

~M~