That, or the spuds are installed on location. Another option to towing is to barge them out, as the Hex bridge caisson from IMFS that I am using as a conceptual reference was actually cast on the deck of a barge. In addition to the EPS foam below the deck for buoyancy, the hex shell itself is also a sealed hull, so there’s lots of reserve buoyancy. Putting the spud legs up in the air for travel is a bad idea, agreed. Puts too much weight too high and poses a capsize risk even for such a stable platform, and lowering them adds drag for a tow situation, agreed. But I don’t think it adds too much drag for a rare operation to be practical.
I am planning to build a scale model using fiber cement board (4’x8’ sheets at Home Depot simulate approximately scaled thickness, 80lbs per sheet)) and just use a wooden frame to screw it together and seal with silicone. I think I can place a polycarbonate (plexiglass) panel in one side and use a ruler for scale with a GoPro for recording wave height. At 1" to 1’ (1/12th) scale a single fiber cement board can provide the hexagon base, and two boards should supply all the walls. I can use 2.5" pipe for spud legs. I will probably just use Pipe Straps on the outside for that rather than constructing a complex internal structure. A couple 4’x8’x2" sheets of foam insulation serve as flotation. 6" would support about 323 lbs, 8 inches about 431 lbs.
I have the Columbia River for my wave tank.
My first impression is that you cannot claim both, gravity based AND buoyant support.
If you jack up (lets say 2’) then you HEX will displace a smaller volume of water than when it was free floating. Therefore, the weight of the volume of water the HEX displaces NOW is LESS than the HEX’s own weight. In consequence, no buoyancy.
Yes, it will be displacing less water than the Hex weighs. But it won’t be displacing zero water, therefore is still a buoyant structure AND a gravity based structure. You may be right that it doesn’t matter from a descriptive or legal point of view.
I should be able to simulate the stability by marking my model, and lifting it/re-fastening a couple inches higher and see how big a wave it wakes to make it move. 2" of foam should provide almost 108 lbs of buoyancy. With 6" of foam in the water, I should be able to stand in the middle of it.
With 6 x 8’ sections of pipe, that would simulate 96 ft of spud leg.
The main benefits I foresee from maintaining partial buoyancy are:
- scaling the deck to longer spans, potentially not necessary in the small hex described here,
- a graceful failure mode for the spud legs, and
- the option to move it at a future point.