A PA18 Pilot reported striking a wingtip during a float takeoff as a gust of wind hit the aircraft. Torn fabric was seen on the lower wing during a cursory inspection but after landing at the home base; tears on both upper and lower surfaces were discovered.

Narrative

I was taking off on the river with my float equipped PA-18 while doing my riverboat demo. A gust of wind picked me off the water before it was ready to fly; then the right-hand wing dropped. While correcting for the wing; the right-hand float hit the water followed shortly by the left-hand float. I kept full power; got it straightened out; and lifted off the water. I then finished my take off and landing demonstration. Upon landing for the demo I was notified by the boat that I may have hit my wing. I got out to look at the plane. While standing on the float I noticed what appeared to be a small tear on the bottom of the left-hand wing. I flew back to my float pond base; a half mile away. Upon tying the aircraft up; I realized the fabric was ripped more than I could see standing on float before I flew it. There was no structural damage to the ribs or wing tip bow; just a larger rip on the bottom as well as one on the top that was not visible from the float. As I am an A&P [with] Inspection Authority I took my plane out of the pond and back to my hangar. I proceeded to repair the fabric damage. I believe that the gust of wind was due to a large thunderhead that was moving into the area. We have had several days for the last week and the wind sneaks up quickly and gusts strongly. I should have assessed the wing tip better before my flight back to the float pond base and acquired a ferry permit for the flight back to the float pond.