Depends on a million things, most notably:
Your position in the log (front is typically wetter than the back)
Your particular log's overall weight distribution
Truly, though, the amount of potential wetness is directly related to how wet you wish to become. If you are hot and willing to get soaked, you will get about 3 drops on your big toe. If you are cold, wearing a white t-shirt and praying for a dry ride, you will look like you went down the drop without a log