Verdant had the top 1/3 of its turbine blades sheared off by the power of the East River. The design of underwater turbine blades apparently was not of sufficient strength. Although water current turbine blades are only a fraction the diameter of wind turbine blades, the forces on these blades are perhaps 50 to 100 times greater due to the sheer mass of the water pushing against them.

The blades may be smaller in diameter and rotate at considerably lower rpm as compared to the wind type but the potential for energy conversion is just as great.

Let us examine kinetic energy. The formula is:
KE = 1/2 m v^2
Kinetic energy equals one half of the mass times the square of its velocity.

1. With wind energy, the mass is about 1/1000 the mass of liquids or solids of the same volume. Much of the energy is due to the velocity portion of the equation. In actual practice, the energy that can be practically converted rises with the cube and not the square of the velocity. There is a minimum start up wind velocity to get the blades moving and then also a second greater minimum velocity (cut-in speed) for the generator to start producing energy.

2. With ocean/river current flow, the mass being about 1000 times greater than air per unit volume means that Kinetic Energy derived from conversion of moving water becomes more mass than speed related.

If we were to compare the two energy sources,

1/2 m(air) x v^2 =
1/2 x 1000m(equal vol water) x v^2

we would then better be able to see that it is not necessary for the velocity of the water to be great in order to provide equitable Kinetic Energy. Actually, the volume of the water passing through the blades of the ocean turbine would have to be only a fraction of the volume needed for an equivalent amount of energy produced by a wind turbine. Thus the need for smaller diameter but much stronger blades for the ocean turbine.

adrianakau@aol.com