I'm betting it was algae on the ramp...I had a scare once with my truck down at the Redondo ramp in Federal Way, WA. due to algae on the ramp, I didn't floor it, I let OFF on the accelerator so that traction would grip (Growing up around snow helps you in situations like this

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a couple years ago, I watched a Toyota launch a boat where we fish in Eastern WA, do the same thing. First, I warned him.."Launch over here, that area is too steep and you'll get stuck in the soft sand..." Advice falls on deaf ears. He launches anyway. Trying to get out, he buries the rear end deeper, deeper, pretty soon water is coming in the passenger door, 1/2 the truck is submerged. Then the guy had the BALLS to ask me for a tow out. I handed him my cell phone..."Call a tow truck, pal".