a dredger for removing sand , silt and like material from a river or seabed has application to clearing wrecks and providing trenches in which , for example , pipeline may be laid . the dredger includes a body having first thrusters to direct , in use , a wash of water downwards an area of seabed . the dredger also includes an additional thruster to maintain the body of the apparatus above the seabed and to propel the body through the water .