There was, once upon a time, a group trying to make some kind of high altitude atmosphere sampling rockets fired from an array of buoys in the Pacific Ocean, powered by Cesaroni motors. No, really! They did tests on Hatzic Lake, about 50km from here.
Their test apparatus consisted of a launch pad on a wooden platform (two 2x4's mounted in a "+", styrofoam floats at the ends, with another 2x4 vertical at the center supporting the launch rail. The ignition wire was strung out across the water with fishing net floats every half-meter or so. These were HPR rockets, so the wire had to be quite long. Also if you didn't have floats on the wire, the sinking cable would try to pull the control boat and launch platform together.
Set it up, putter away, wait until there are no jet-skiiers around, hit the button, WHOOSH, disconnect the leads from your control box, drive off to get your rocket, come back for the platform and wire.
The real system would have had these stabilized boat-like buoys out in the ocean, each with >200 rockets, with launch controlled by a sensor that identified when the launch tube was vertical.