During the early morning hours RS#40 was making way (under motor power at 5 to 6 knots with 850 RPM) with a building light to moderate sea. At approximately 0830 UTC, all crew noticed the vessel decelerate and one off-watch crew-members was thrown out of their bunk onto the sleeping quarters floor in open water >100m. Within minutes flooding seawater was observed above the main cabin and engine room floor of the vessel. All mechanical and electrical pumps were submerged in minutes and crew was forced to abandon ship.