TI (the novel) need not be "realistic", since it is a part of reality itself, as referred to in "Peter Pan", "Pirates of the Carribean" etc. Any new adaptation may or may not stick to the original or its historic foil, it will be judged by what new aspects it adds. I am disappointed by the "Pirates of the Carribean" and do not plan to watch the TI film at the moment.

MtheGM, you are probably right about the anachronism, but note the poetic density of the short passage you quoted. Not many novels for the youth were written in such a powerful language. The "shanty" function illustrates the disciplined collective effort of the pirates, contrasting their desolate characters reflected in the sinister lyrics. Poetic license must be granted.