Verdant Power has been testing the use of underwater turbines in New York's East River for the past few weeks, with the goal of adding hundreds or even thousands of turbines to help address the city's power needs.
There's just one minor problem - the current is so powerful that the turbines are snapping like twigs. While the turbines have been temporarily removed, Verdant is hopeful that a redesign will allow for greater power generation with fewer malfunctions.
Link [NYTimes] via Gothamist
Well, you may not be a civil engineer, but the issues involved don't pertain to civil engineering anyhow... it's Mechanical Engineering or Aeronautical Engineering, ME's fluid mechanics-heavy brother. The turbine design resembles a wind turbine because the goals are similar. Air and water are BOTH fluids (fluid liquid).
The design is more influenced by the expected tip speed and available real estate. On a boat, the propshaft turns very very fast (much too fast for a big diameter prop) and available real estate under the boat is limited anyhow. The situation is different with these guys. Also, efficiency is much more important here than with a typical propellor design as well (big slow turbines can be very efficient). Furthermore, these guys can be optimized to have a much more narrow band of operation. A boat prop, by its nature, will see a greater variation in its rotational speed.
Don't lose sleep over this ... Something tells me that the people who design these things use some high powered computational fluids dynamics modeling packages to get the design pretty good.