text: The weight a foil can lift is proportional to its lift coefficient, the density of the fluid, the foil area and its speed squared. The following shows the lifting ability of a flat plate with span 10 metres and area 10 square metres moving at a speed of 10 m/s at different altitudes and water depths. It uses the lift at an altitude of 11 km as a datum to show how the lift increases with decreasing altitude (increasing air density). It also shows the influence of ground effect and then the effect of increase in density going from air to water. 
   height 11 km:        lift  1.0 (datum for comparison)
          5 m                 3.4
    in ground effect          4.1
   water surface-planing     1,280
   just submerged            1,420
   depth  5 m                2,840
        10 km                2,860