The 21 meter long tug En Avant 5 capsized on the Maas River near Dordrecht, Netherlands.   The tug was engaged with another tug dragging a barge when it capsized.   The 4 crewmen on board were able to jump safely into the water.   A ferry picked up the men who were taken to hospital to be checked out.   The En Avant 5 is still attached to the barge.    The cause of the capsizing is not known.   Authorities are conducting an investigation into the incident.