good idea.
Here's an alternate
Spar Bouy concept. Some Oil Platforms are made this way.
RedNeckversion would be to use stacked 55 gallon barrels mounted to a swivel (truck axel?)
Build it on land. Tow it to where you want it. Flood the barrels. (except the last one, it's full of concrete). When the spar rotates under the platform, pin it in place, then pump air into the flooded barrels. (one after the other top down first) The added flotation will raise the platform above the water, waves will pass under.