Abstract: Floating hydrodynamic fin system, useful for surfboard and windsurf, modifying its fin lift trim by a calibrate and controlled spring and an asymmetric shape of the fin-base that leaves a gap between said fin-base and the fin-box, allows the floating of the system rearward and/or forward. This happens by: 1) reducing the resistance of the water flow against the fin. 2) influencing the critical point of the board by the vector lift force displacement rearward in one or more critical times. 3) reducing the fin lift surface due to a part displacement of the fin into the fin-box. Said system can also works by a limited and calibrated movement of a fin-box into another fin-box controlled by a spring calibrate device and by a suitable fin-box shape that leaves a gap between the inside and outside box allowing the floating of the system.