Valmai, I have deleted my cookie put this as I wish in this instance to submit as a guest. As you suggest the regatta is determined by the tide, if however the regatta had been held a fortnight earlier as is often the case (13/14/15 August in 2011, 10/11/12 August 2013, 9/10/11 August 2014 .... you get the picture) the difference in the tides would have been as follows (All times GMT)

Date    High Tide    Height      Date   High Tide   Height
Friday 6 13.19         4.4m       Friday 20