Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Ship's name | Date entered service | Date withdrawn | Tonnage | Type of Ship |
| --- | --- | --- | --- | --- |
| Oranje Nassau | 27 August 1945 | July 1954 | 3053.0 | Twin Screw Steamer |
| Mecklenburg | 21 November 1945 | 25 October 1959 | 2907.0 | Twin Screw Steamer |
| Koningin Emma | 5 March 1948 | December 1968 | 4353.0 | Twin Screw Motorship |
| Prinses Beatrix | 31 May 1948 | September 1968 | 4353.0 | Twin Screw Motorship |
| Koningin Wilhelmina | 7 February 1960 | 1 July 1978 | 6228.0 | Twin Screw Motorship |
| Koningin Juliana | 17 October 1968 | 8 April 1984 | 6682.0 | Twin Screw Ro-Ro Motorship |
| Prinses Beatrix | 29 June 1978 | May 1986 | 9356.0 | Twin Screw Ro-Ro Motorship |
| Prins Oberon | 11 February 1983 | 11 March 1983 | 7993.0 | Twin Screw Ro-Ro Motorship |
| Zeeland | 1 April 1984 | 25 March 1986 | 6801.0 | Twin Screw Ro-Ro Motorship |
| Armorique | 25 March 1986 | 16 April 1986 | 5731.0 | Twin Screw Ro-Ro Motorship |
| Koningin Beatrix | 16 April 1986 | 2 June 1997 | 31189.0 | Twin Screw Ro-Ro Motorship |
| Duchess Anne | January 1989 | February 1989 | 9796.0 | Twin Screw Ro-Ro Motorship |
Question:
what is the sum of tonnage when the type of ship is twin screw ro-ro motorship and the date entered service is 11 february 1983?
Answer:
7993.0