Just how many......

[lesrae]

From http://www.globalsecurity.org/milita...-ro-safety.htm (this goes back more than 25 years)

The first ro-ro ship to be lost at sea was the Princess Victoria, a rail ferry which sank on a voyage to Belfast in 1953 when heavy seas stove in the stern door: 133 lives were lost. At least 264 people died in 1966 when the Greek ferry Heraklion sank in heavy seas on a voyage to Piraeus. Although not a ro-ro, the ship did have a large car deck without subdivisional bulkheads. This deck flooded when the loading hatch was smashed by a vehicle which had broken loose. The cargo ro-ro Hero was lost in 1977, partly as a result of water entering through a leaking stern door. In September 1994 the passenger ro-ro Estonia was lost with more than 900 lives when the bow door was torn off by heavy seas. The car deck flooded and the ship capsized within a few minutes.
These accidents happened in heavy seas, but other ro-ros have been lost through water entering doors in port or sheltered waters. They include the Straitsman, which sank when the stern door was opened as the ship approached land, with the crew unaware that the door sill was below the waterline: and the Seaspeed Dora, which capsized in 1977 when a movement of cargo caused the ship to list sufficiently for water to enter through an open bunkering door. In the case of the Herald of Free Enterprise, water entered through the bow door which had been left open.
Ro-ro ships which have sunk rapidly as a result of a collision have included the Jolly Azzurro (1978), Collo (1980), Tollan (1980), Sloman Ranger (1980), Ems (1981), European Gateway (1983) and Mont Louis (1984). Among ships which have been lost following a shift of cargo are the Espresso Sardegna (1973), Zenobia (1980) and Mekhanik Tarasov (1982, in very bad weather).