The steamship Oranje Nassau
In February 1911, the steamship 'Oranje Nassau' was launched, built for the Royal West Indies Mail Service. The ship was built by the Royal Company 'De Schelde' in Vlissingen and could carry 62 passengers and 214 deck passengers. 
In 1927, the ship was transferred to the Royal Netherlands Steamship Company.
Envelope with stamp impression
In a bin of mail items during Postex 2010 in Apeldoorn, I found an envelope with a stamp impression that I only knew from books: an elongated stamp with the letters KNSM and the name of a ship, SS Oranje Nassau.
Furthermore, the date July 24, 1936. Such stamp impressions did not appear in the stamp books of the Museum for Communication in The Hague. So, I continued searching. On the website of the South-West Pacific Study Group, I also found such an impression, but dated August 22, 1932, on a stamp from Curaçao. The difference was that a dividing line between Orange and Nassau appeared in the 1932 stamp.
In a book by Dr. J.D. Riddell, I found many more names of ships that can appear in the stamps.
The letter was addressed to Booker Bros. McConnell & Co., Water Street in Georgetown (Demerara). The name Demerara is the name of the former Dutch colony that was ceded to the British in 1814. The capital, Stabroek, was renamed Georgetown. Upon arrival, an impression of the Paquebot stamp British Guiana was applied.
In 1939, the ship was sold to a Greek company, Hellenic Mediterranean Lines in Piraeus, which changed the ship's name to Corinthia. The ship sailed for this company for almost another 10 years, after which it was scrapped in La Spezia, Italy, in October 1958. Such a simple envelope with so much history! 
Does that rectangular stamp also fall under the Paquetbot stamps?
Jos, the PAQUEBOT stamps form a category of their own. Several seaports in the Netherlands received these stamps (Vlissingen in May 1900, Rotterdam in October 1901, etc.) to stamp foreign mail items, franked with foreign stamps, at the post offices in those seaports. Sometimes the impression of the stamp was on the foreign stamps, sometimes next to them. In the latter case, the foreign stamps were cancelled with the date stamp of the post office. If a letter was posted on a Dutch ship, franked with Dutch stamps, and the letter was sent from a foreign seaport, then the stamps were cancelled at that foreign post office with the PAQUEBOT stamp of that post office. A very nice collecting area!!
I have a stamp from the 1876 numeral series, the 2,5 cent yellow/olive; it says KATWIJK in block letters, exactly as it appears, no box, and the bottom is not serrated or cut off.
Does anyone have an opinion on that? No idea what it's supposed to be.
Henny, do you mean a kind of stamp like in the following reference?
http://www.vandieten.nl/artikelen/oosterwolde/
No Toon, the stamp is actually on just the postage stamp, so it's not part of the postal item. I don't think I could scan it and show it, otherwise I would have gladly done so. Thanks for thinking along anyway, Toon.
Just a correction; it is the 2 cent and it says ATWIJK-B, that's why I don't look at it every day. I assume that the B stands for boat; it is not a standard cancellation according to the NVPH, although some stamps were indeed cut off, but whether that was the case with mine too, who knows?
Henny, the impression probably comes from the office name stamp (they used to say 'long stamp', but that is not a formal designation) KATWIJK-BINNEN. This name stamp was issued on October 18, 1870, and was used until March 16, 1892, when the name of the auxiliary post office was changed to KATWIJK A/D RIJN. This new designation was prescribed as early as 1888 but was not applied until 1892. The auxiliary office itself was established on September 1, 1850, and belonged to the jurisdiction of the Leiden post office.
Thanks Cees,
Good to know, I have a batch of that series, trying to get it somewhat complete: the perforations type 1 and 2, the comb perforation, Bosche perforation, color, etc. It's not even that easy a series for me, at least; sometimes I have doubts, especially with the Bosche period, where there are sometimes diamond-perforated stamps (including cut-off ones) with small and large holes. Is the 1923 jubilee series easier? I have that one fairly complete already too, though the unperforated perforations are a bit more difficult given the prices. But then again, as a Germany collector, you do learn a thing or two; I don't think I need to explain here how far our neighbors go. Horizontal and vertical rubber, and I'm crazy enough again to collect everything from German states, the Reich, the East and West Occupation Zones—a so-called omnivore. Oh well, it is educational, and I have to do it myself anyway; sometimes doubt is inevitable. It is nice when you can help each other sometimes, even though philatelists are generally loners; I've never understood why.