When I lived in Humboldt County , the competitive Kinetic Sculpture racers held around that Bay, on Memorial Day weekend , competing in fastest time category ;

used the inflatable Catamaran style pontoons for day 2 which is the Water crossing .. They Built a Recumbent Tandem Tricycle frame, the pontoons carried but not Deployed ..
Kinetic Grand Championship - Humboldt County, California.. Kinetic Grand Championship - Humboldt County, California // Kinetic sculpture race - Wikipedia, the free encyclopedia

predominantly is more about Art, than speed .. https://www.youtube.com/watch?v=_VYTnLqcXks

begin building .. .. As your 1st photo Showed .. that uses a regular bike,, a frame to fit those mounts .

Can even hinge the pontoon supports , so as to make your Proposed. 3 wheels contact the road on dry ground..
that's what the competitors did .


now there is the 4" fat bike wheel , 20 years ago for width 5 MTB rims were strapped side By side to get adequate Flotation

or ATV wheels were Used..