Wiktionary
disrating
vb. (present participle of disrate English)
Usage examples of "disrating".
The punishment book, which Bolitho had inspected first, and which he always considered to be the safest measure of a ship's captain if not the performance of his command, showed the usual list of petty offenders, with the punishments of flogging and disrating no more or less than one might expect.
It means disrating a midshipman - degrading him, so that he is no longer what we call a young gentleman but a common sailor.