order to automatically control the boat 39 s buoyancy allowing the cabin 1 to smoothly float atop the surface of the water fig3 shows the cabin 2 on top of the surface of the water 5 with only the counterweight underwater there is only air inside the space 41 fig4 shows that when the cabin needs to be submerged first the inlet valve at the bottom part of the space 41 is opened to allow water to flow into the space the specific amount of water that enters the space 41 depends on the buoyancy of the part of the cabin that is descending when the weight of the water in the space 41 becomes greater than the buoyancy created by the cabin 2 the lifting mechanism 3 begins to operate for example the winding engine 31 begins to tighten the dragline 32 and its direction of movement is as shown by the arrow in fig4 causing the cabin 2 to start descending at the same time water is continuously flowing through the inlet valve into the space 41 causing the buoyancy and weight affecting the entire vessel to reach a balance when the cabin 2 descends to the determined level the lifting mechanism 3 stops the inlet valves close and the boat is in its semi submerged state as shown by fig5 allowing personnel to start underwater operations or allowing tourists to view the underwater scenery when the boat needs to be returned to its normal state engage the lifting mechanism 3 for example the winding engine 39 s power discharging device through its natural buoyancy the boat cabin 2 can rise above water level 5 at the same time.