Oops
"Once it begins to bounce, the air is heated, say burning natural gas. And also compress air is added. How much the air is heated and compressed air is added controls the acceleration. At about 1000' above the water"
I should have said "about 750' above the water"
[I was orginally planning on a total pipelauncher length of 1400' but I edited it to 1000, after the numbers told a different story:]