Explainer
Self-ballasting cover — mechanism reference
A self-ballasting floating cover holds position on the water by carrying its own ballast — either water entering on install (the 2010-patented original Hexprotect®) or ballast sealed inside the moulded shell at the factory (Hexprotect® AQUA).
A self-ballasting floating cover is a modular floating cover whose elements hold position on the water surface by carrying their own ballast — no anchors, no cables, no perimeter tensioning. The AWTT-patented line covers two retention mechanisms: the original self-ballasting design (2010 patent, water entry on install) and the pre-ballasted refinement (Hexprotect® AQUA, sealed factory ballast).
What is self-ballasting?
In a self-ballasting floating cover, the element carries its own mass on the water — typically water itself, as ballast — and stays in position by buoyancy, ballast mass, and the friction-and-overlap of the tessellation. The defining contrast is with continuous geomembrane covers, which retain the cover surface by anchoring a single sheet to fixed points at the shoreline. Self-ballasting eliminates the entire anchor system as a capex and maintenance line.
How self-ballasting works — the original Hexprotect® mechanism
The original Hexprotect®, patented by AWTT in 2010, is the canonical self-ballasting hexagonal floating cover. Each tile is a hollow hexagonal HDPE element with carefully placed side ports:
- Water entry on install. When the tile is launched onto the water surface, water enters the tile through the side ports and ballasts it to the engineered draft.
- Light exclusion geometry. The port placement and the dome profile prevent direct sunlight from entering the internal chamber — critical for keeping the tile from harbouring algae or biofilm.
- Drain on retrieval. The same port geometry lets water drain back out cleanly when the tile is lifted from the surface.
The 2010 patent grant covered the self-ballasting design as a whole — the world’s first self-ballasting hexagonal floating cover. The mechanism worked, and it remains the engineering foundation of the AWTT line.
Why pre-ballasted replaced self-ballasting as the workhorse
Through the 2010s, AWTT field-tested the original Hexprotect® at scale across mining, water utility, and biogas deployments. Three operational shortcomings surfaced:
- The open ballast chamber harboured biological growth. The chamber’s internal volume was difficult to inspect or clean once the tile was in service. Algae, biofilm, and accumulated sediment built up over years.
- Tipped tiles lost ballast water. When a tile was disturbed (storm wave, debris impact, retrieval) and tipped past the port height, ballast water drained back into the water body. A re-ballast event was required to restore the tile.
- Narrower side walls allowed tessellation drift. The original side-wall profile gave the tessellation less lateral hold under sustained wind. Tiles could spread, opening seams that violated the AWTT-published 99% coverage assumption.
Hexprotect® AQUA — released commercially in 2009, before the 2010 patent grant — addressed all three by sealing the ballast inside a one-piece moulded shell at the factory. The chamber is no longer open to the water body. Ballast cannot be lost on tip. Side walls were raised. The outer surface was smoothed so debris and dirt shed naturally.
See /heritage/hexprotect-aqua-refinement for the six engineering refinements and the lineage detail.
Benefits of self-ballasting / pre-ballasted retention
| Benefit | Detail |
|---|---|
| Anchorless install | No anchor system to specify, install, or maintain. |
| Installs on operating water | No draining, no service interruption — see /installation. |
| Tolerant of irregular shorelines | Tiles pack around inlets, outlets, and bay geometry. |
| Tolerant of water-level changes | Tiles rise and fall with the surface without losing position. |
| No external infrastructure | No tensioning cables, no perimeter anchors, no specialist crew. |
| Lowest 10-year TCO | No anchor replacement, no membrane re-tensioning, no drain-down. |
When to specify self-ballasting / pre-ballasted
- Surface-management goals are evaporation, algae, odour, or heat (not biogas capture).
- The water body cannot be drained for install (operating reservoirs, active tailings ponds, live digester adjacent storage).
- Capex sensitivity is real, and the anchor-system line is the deciding factor.
- Surface geometry is irregular, or water levels fluctuate.
For deployments that require gas capture or full environmental containment, continuous geomembrane is the right call — see the engineering comparison at /floating-cover.
Self-ballasting vs pre-ballasted — quick reference
| Property | Original Hexprotect® (self-ballasting) | Hexprotect® AQUA (pre-ballasted) |
|---|---|---|
| Patent | AWTT, 2010 | AWTT line refinement; release 2009 |
| Ballast | Water entering on install | Sealed factory ballast |
| Internal chamber | Open to water body | Sealed |
| Algae harbour | Yes — operational shortcoming | No |
| Ballast loss on tip | Possible | No |
| Side-wall profile | Lower | Raised |
| Outer surface | Recessed | Smooth, debris-shedding |
| Production status | Retired | Current workhorse |
Sources
- AWTT — Hexprotect® AQUA hexagonal cover — manufacturer’s canonical product reference; patent-history and engineering-evolution source.
- /heritage/original-hexprotect — full original Hexprotect® invention story.
- /heritage/hexprotect-aqua-refinement — the six engineering refinements AQUA applied.