Romanian Danube Delta Ship Mail

In a previous post, I asked if anyone had information on the postmark shown below. but I did not receive any responses. I have since discovered the answer. Apparently the postmarks were created by the Navigatia Fluviala Romana or Romanian River Service, which operated a mail service in the Danube delta from 1890 until World War One. Postmarks exist between Sulina, Tulcea and Galati and reflect the direction of travel eastbound or westbound.