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In 1952 Yugoslavia issued an attractive maritime set, of which the 10 dinars value is alleged to show the post-war motor liner Zagreb. If this is so, the stamp exaggerates the vessel's size and is quite wrong as to her appearance for, according to "Lloyds Register," she is only 3,100 gross tons on dimensions 317.8ft x 45.9ft. x 27.4ft and has her propelling machinery aft! She was built by Poduzece III Maj. at Rijeka.
SG668 Sea Breezes 8/51

The vessel depict on this stamp is one of four ships built in the 1950s for the Jugoslovenska Linijska Plovidba in Rijeka, Yugoslavia by the yard of Poduzece 3 May, Rijeka.
The first built was the ZAGREB, she had three sisters the SKOBJE, SARAJEVO and TITOGRAD. Which is depict I am not sure, most probably the first built the ZAGREB.
She were used in the liner service between the Adriatic and Cyprus to Egypt.

Built as a cargo vessel under yard no 239 by Poduzece 3 May at Rijeka for Jugoslovenska Linijska Plovidba, Rijeka.
Launched as the ZAGREB. Three sisters.
Tonnage 3,265 grt, 1,763 nrt, 3,905 dwt, dim103.4 x14.0m, length bpp.93.0m.
Powered by one 2SA 7-cyl. diesel engine, manufactured by S.A. Fiat S.G.M. , Turin, Italy., speed 13.5 knots.
July 1949 completed.

She was broken up by Brodopas in Split, Yugoslavia were she arrived March 1979.

Yugoslavia 1950 10d sg668, scott? (Could not find a photo of the ZAGREB, only of the TITOGRAD, she is the same as the ZAGREB.)
Source: http://www.miramarshipindex.nz Lloyds 1955/56