Institute. He produced a number of studies including analysis of tides which identified the presence of a "virtual amphidrome" in the region. Heath also quantified a best estimate for the time of the "residual current" (i.e. net current after averaging out the tidal influence) in the strait. This continues to be a topic of research with computer simulations combining with large datasets to refine the estimate. Despite the strong currents, there is almost zero tidal height change in the centre of the strait. Instead of the tidal surge flowing in one direction for six hours and then in the reverse direction for six hours, a particular surge might last eight or ten hours with the reverse surge enfeebled. In especially boisterous weather conditions the reverse surge can be negated, and the flow can remain in the same direction through three surge periods and longer. This is indicated on marine charts for the region. Furthermore, the submarine ridges running off from the coast complicate the ocean flow and turbulence. The substantial levels of turbulence have been compared to that observed in the Straits of Gibraltar and Seymour Narrows in British Columbia. Tidal power The electrical power generated by tidal marine turbines varies as the cube of the tidal speed. Because the tidal speed doubles, eight times more tidal power is produced during spring tides than at neaps. Cook Strait has been identified as a potentially excellent source of tidal energy. In April 2008, Neptune Power was granted a resource consent to install a $10 million experimental underwater tidal stream turbine capable of producing one megawatt. The turbine was designed in Britain, and was to be built in New Zealand and placed in of water, due south of Sinclair Head, in waters known as the "Karori rip". The company claimed there is enough tidal movement in Cook Strait to generate 12 GW of power, more than one-and-a-half times New Zealand's current requirements. In practice, only some of this energy could be harnessed. As of October 2016, this turbine had not been built and the Neptune Power website is a placeholder with no further announcements. On the other side of the strait, Energy Pacifica applied for resource consent to install up to 10 marine turbines, each able to produce up to 1.2 MW, near the Cook Strait entrance to Tory Channel. The company claimed that Tory Channel was an optimal site with a