I wouldn't stake my life on it, but I think that Boot came before Schiff. Bremse was built for the Reichsmarine, befopre the Kriegsmarine was created and at that time the artillery training vessels were Artillerieschulboote. I have seen a photo of her described as Artillerieschulboot with the Reichsmartine flag, so my guess is that she was originally known as an Artillerieschulboot and later classified as an Artillerieschulschiff. A "ship" is generally considered bigger than a "boat", and Bremse was about the size of a biggish destroyer /light cruiser (the lighter German destroyers were of course known as Torpedoboote, again going with the smaller vessels being classed as "boats".
Thats my take on it anyway (but I could be completely wrong )