Research is being carried out on the possibility of using off shore turbines, driven by the power of the tides. The powerful tides could be used drive under water turbines. The turbines could rotate in either a clockwise or anticlockwise direction and as the tide is always moving, electricity production would be continuous. As they are based well away from land they are out of sight and, unlike wind powered turbines, they do not create noise.
The major difficulties with this type of system is that the off shore turbines cost more money than land / wind based turbines and they are also more expensive to maintain as they function under water. Furthermore, sea water is corrosive to steel and other metals because of the salt content.
The drawing below shows how the propellers would be maintained using large maintenance ships. When maintenance is required the propellers would be extended above the water. The plan is for the turbines to be sited together similar to wind farms on land and the generated electricity to be cabled to the land.

QUESTIONS:

1. What are the disadvantages of an off shore tidal system?

2. What are the advantages of an off shore tidal system?