Dutch, Deutsch from *thiudisk = "belonging to the people". Originally it had nothing to do with a special ethnic group, but in the realms of the Eastern Francs it took its modern meaning of Deutsch and Dutch for groups of speakers of these languages. It has nothing to do with teutonic, albeit its latinized form may sond similar.
Due to certain difficulties of pronunciation in America Dutch was preferred not only to denote the Netherlanders but the Germans (Deutsche), too. Try to pronounce it doytch, oy as in boy.

Zider Zee (?) = Zuiderzee (~21.100 hits in Google) or Zuijderzee (30 hits) = Southern Sea. The latter seems to be the older orthography.

Jolly good song. Where can I find the tune?

Wilfried