Motor ships of the types VELIKIY (project 550) and VOLGONEFT (projects 550A, 558, 630 and 1577) are the big decker tankers of the "river-sea" class with forecastle and quarter-deck, with double boards and double bottom, with machine compartment and superstructure in the rear part. It is the largest series of tankers of such class, intended for carrying of crude oil and oil products.
Modifications. Initially ships of the projects 550 and 558 were built. These projects are practically identical in their construction and characteristics. As it is presumed, project 550 is the designation of the foreign-built ships. Ships of the two types slightly differ in the 

details of the superstructure. Later the project was modified (project 1577), cargo-carrying capacity was reduced a little, pipeline equipment was changed, more modern superstructure was designed. As it is presumed, such tankers were built abroad as the project 550A. Outwardly ships of the project 1577 and of the project 550A are distinguished from each other by the design of masts, later-built ships - also by the form of funnel. Later the ships were deleveloped (project 630) which were strengthened for sea navigation and navigation in ice. They have increased length, draught, machine power, higher productivity pipelines and modern superstructure. As a continuation of the series of the type "Volgoneft" the tankers of the type "Oleg Koshevoy" ("Kaspiy") were built.
Motor ships of the project 558 were built since 1962 till 1967 in the USSR, motor ships of the project 550 - since 1963 till 1971 in Bulgaria. About 80 units of the both projects were built. Soviet and bulgarian-built ships were assigned serial numbers (soviet: 1 - 30 and assum. 52 - 66 numbers; bulgarian, from Rousse: 31 - 45 numbers, from Varna: since 46 number). Motor ships of the project 1577 were built since 1967 till 1979 in the USSR; not less than 70 units were built. Ships of the project 550A were built since 1969 till 1982 in Bulgaria; 65 units were built. Initially ships were assigned serial numbers from the common serial order with the letter "M" added to the name. Later they were renumerated and the new numeration was started. Soviet-built ships were assigned numbers starting from 201; bulgarian-built ships - numbers from 101. Motor ships of the project 630 were built since 1984 till 1996 in Bulgaria; up to 10 units were built.