A rig unit for a fishing line, including: - a float body, having a main axis, a front end, with reference to the orientation in flight, and a rear end, and - a ballast mass, removably coupled to the float body, - wherein the ballast mass and the float body are configured to remain coupled together during the launch phase and flight, and to separate from each other upon impact with the water at the end of the flight path, - wherein the ballast mass has a front end removably coupled to said rear end of the float body, and a rear end provided with a guide passage for a main line connected to the float body, - said float body of the rig unit having an attachment element to which a terminal line is connected and a connecting element (02, 53) to which said main line is connected, - said terminal line having one end connected to the attachment element of the float body and an opposite end with which a hook can be associated, said rig unit being characterized in that: - said opposite end of the terminal line carries an auxiliary float, and - the ballast mass is configured to rest on the seabed, in such a way that: - during flight, when said float body and said ballast mass are connected together, said rig unit is orientated with the float body arranged in front, and the ballast mass arranged behind it, while - after that said float body and said ballast mass are separated upon impact with the water at the end of the flight path, the ballast mass rests on the seabed, so that the main line is arranged with a first section descending from the fishing rod until the aforesaid guide passage of the ballast mass resting on the seabed and with a second section ascending from said guide passage of the ballast mass up to said float body, with said float body that, in this way, is able to remain immersed, at a distance from the water surface, and with the terminal line arranged in such a way as to extend upwards, starting from said float body, up to said auxiliary float. - a float body, having a main axis, a front end, with reference to the orientation in flight, and a rear end, and - a ballast mass, removably coupled to the float body, - wherein the ballast mass and the float body are configured to remain coupled together during the launch phase and flight, and to separate from each other upon impact with the water at the end of the flight path, - wherein the ballast mass has a front end removably coupled to said rear end of the float body, and a rear end provided with a guide passage for a main line connected to the float body, - said float body of the rig unit having an attachment element to which a terminal line is connected and a connecting element (02, 53) to which said main line is connected, - said terminal line having one end connected to the attachment element of the float body and an opposite end with which a hook can be associated, - said opposite end of the terminal line carries an auxiliary float, and - the ballast mass is configured to rest on the seabed, in such a way that: - during flight, when said float body and said ballast mass are connected together, said rig unit is orientated with the float body arranged in front, and the ballast mass arranged behind it, while - after that said float body and said ballast mass are separated upon impact with the water at the end of the flight path, the ballast mass rests on the seabed, - during flight, when said float body and said ballast mass are connected together, said rig unit is orientated with the float body arranged in front, and the ballast mass arranged behind it, while - after that said float body and said ballast mass are separated upon impact with the water at the end of the flight path, the ballast mass rests on the seabed,