According to people who saw the race they estimate that the boat was traveling more than 85 mph. The boat is question is a Nordic 35 Flame. The 35 Flame incorporates a twin-stepped hull design.
For those of you who are not familiar with performance boats the "steps" that modern performance boats have incorporated in hulls of their boat are put there by manufactures in order to trap air under the hull and reduce friction.
Now these steps have been a great advancement in performance boating in that they allow boats of similar size and horse power travel at speeds much greater than their counterparts of a few years ago. However, there is a downside. The air trapped under the hull that allows them to travel 7 to 8 mph faster in a straight line makes them inherenlty unstable in turns.
Now what happens is that if you turn these stepped boats too sharply at high speed the center of gravity switches from the front to the rear. So instead of the boat turning and traveling in the direction that the nose is pointing, the trapped air under the hull causes the the boat to break is grip with the water and continue in the same direction, but rear-first. So now the boat is still traveling at a high rate of speed but backwards. At some point the Swim platform digs in and they come to a sudden stop and incur heavy damage to the rear of the boat - often flipping and ejecting the occupants into the drink.
It sounds to me that boat simply became unstable when he turned to avoid the log and he spun it. It either swamped when traveling backwards or the damage to the rear allowed it to take on water.