I am sure the crack started while the boat was loaded on the "trailer". This was just a rig of two 16" bicycle wheels connected by tubing, which was wrapped in foam. The boat was loaded very heavily.
I won't be using that trailer again because I lost it on the rapids the first day on the Mississippi.

However, I didn't notice any flooding until later, on Lake Winnibigoshish. I was paddling cross-wind most of the day, taking the waves broadside, and I believe the flexing caused by these waves contributed to the length of the crack, but it could be I just didn't take notice before that.