Device making posssible from the dock of a pleasure port to launch boats as well as to take them out of the water, to transport the boats by road and to store them in a garage or boathouse, without the cooperation of any crane or make-up lifting system. A cradle (2) fitted with wheels and which may take two positions, lower or upper, supports the boat and is introduced by rolling into the U-shaped frame of a trailing vehicle. Thereby, only the cradle (2) is immersed, thereby avoiding contact of the trailing vehicle with the water. Additionally, taking into account the combination of said cradle and the "U" of the trailing vehicle, the centre of gravity of the assembly may be considerably lowered. The invention applies to the transportation and launching of any type of pleasure boats of medium tonnage.