I know that the Oertz Flying boats 41-46 were sent to Flanders for testing, and so were flown from Zeebrugge.
Best from Regulus *
Actually the Naval numbers 41 to 46 were used for a number of different flying boats from different manufaturers (if my sources are correct, the Batboat discussed above was one of them, with the naval number 44).
Only no 46 was an Oertz design. Actually, this was the only Oertz FB 3 (FB for FlugBoot = Flying Boat) build.
Not much more that I know of the FB 3, beside the fact that it followed rather standard Oertz design, with the engine (a Daimler D I) buried inside the fuselage and driving a pusher prop via what seems to be a chain drive. It seems that the FB 3 was a more conservative adaption of the earlier FB 2 (which had a substantially bigger lower wing, compared to the upper one).
Max Oertz of Hamburg/Reiherstieg is described in contemporary sources as a "famous boat/yacht builder", which might explain why he ended up building flying boats.
Obviously, the FB 3 did not fare that bad, as Oertz later build and delivered some developed versions (notably the W 5, of which some data and photos exist, and the exotic tandem biplane/quadroplane "Flugschooner). But even Oertz mainly build some (Sablatnig) floatplanes in licence, before selling his aircraft business to Brandenburg in 1918.
ThereŽs not much to be found on Oertz flying boats, but you might find something in the Motorbuch Verlag book on "Deutsche Flugboote" and the book on German flying boats and floatplanes in the series "Die deutsche Luftfahrt" by Bernhard & Graefe(guessing only, I have seen both books, but did not buy them or look that close either).