The floatability of platforms can be increased to twice the buoyancy of air volume if the structure is placed with the bottom open to the ocean, as of diving bell. As the structure is inserted in the ocean the air inside is trapped and compressed which exerts an upward force. If an external air compressor is used to pressurize the air within the structure then , the air pushes the water content to the edge of the open structure. Thus increases the pressure and increases the buoyancy as well as the upward force exerted by the air.By this way we can increase the load carrying capacity by twice,
The keyword to google it is “caission”…
But the caisson doesn’t float , they are rested on the solid bed of water bodies.https://drive.google.com/file/d/1wN1FLqRTPbPYKi21kuZmfgwNoXH7q3kR/view?usp=drivesdk
Yeah , it may not increase the buoyancy force but it can reduce the vibrations due to surface waves in ocean.
I had research such “reverse buoyancy” floating structures years ago. My major concern was that in high seas, due to the wave action, air will end up underneath the “hull” and create a gradual loss of buoyancy.
As long as air can be pumped in to compensate, everything will be OK. But if not, in case of a major electric failure to the air pumps, that baby will go down like a rock.
Way too risky when people lives are at stake. IMHO
If the open surface is left at the surface of water , then it is vulnerable to such circumstances, but the surface is deep inside the water hence the waves cannot affect it. If we are affected by the rough Climate then instead of pumping in air , we can suck air to create the vacuum pressure which can hold the platform tight to the surface https://drive.google.com/file/d/11iCkxM_NNbwdQ8taWGIzlnRBOClZF_q0/view?usp=drivesdk