At present, offshore placers are generally exploited by means of traditional dredging equipment. This technique, called the "vertical method," consists of working the seabed directly from the surface support vessel through a rigid upflow pipe equipped, when necessary, with a sediment preloosening system. In contrast with the vertical method, this approach is based on the principle of working along the seabed with transfer of spoil up to the surface after extraction. We therefore call this the "horizontal method." Although it varies according to sites, in most cases this method comprises the design of a vehicle, self-propelled to some degree, which moves along the seafloor, carries and operates the appropriate mining tools and includes a system to transfer the collected spoil up to the surface for processing. This horizontal method is the approach choosen, studied and developped by offshore mining Group.