Gibb Sahib

So now is the question, is that "Plattedeutsh" is the same as "Hamborger Platt", I cannot answer this question and need to be researched further, and is not an easy case for me, here one of German explanation of the case:

...Platt or Plattdeutsch is the slang term for the Low German language. This consists of a large number of local dialects, which are often provided with the place name to distinguish them, for example, Oldenburger Platt, East Frisian Platt, Sauerländer Platt, or Heidjer Platt spoken in the Lüneburg Heath.

Wooden beams with the inscription
The term "Heidjer Platt" belongs, like other dialects, to different Lower Saxony dialect groups: to North Lower Saxony in the northwest and to Ostfälisch (Heideostfälisch) in the southeast. The dividing line runs roughly along the Uelzen-Celle-Wedemark line. These dialects can still be found frequently in everyday life today. Neighboring dialects are Holsteiner Platt, Hamburger Platt, the dialects around Bremen, and the East Westphalian dialects further ...

source:
naturpark lueneburger

Seems to be related, but are they pronounce exactly the same?
So maybe you have some other sources, which is giving some light, how German sailor language sound, or you just base of note from "Shanties From the Seven Seas"?