To prevent overturning of a CB-series buoy system and to ensure that it is stable in the water, ballast weight may be needed. The center of gravity of the buoy is somewhere near the water surface without instruments connected. Any weight added above the water surface must be appropriately counterbalanced by adding ballast weight below the surface.
The larger the distance from the location of added weight to the center of gravity, the greater the effect on the stability of the buoy will be. For example, if a weather sensor is mounted 36″ above the water surface, it will cause more instability than if it were mounted 24″ above the surface and, as a result, would require more subsurface ballast weight to counterbalance the buoy. Conversely, a ballast weight added further below the surface will provide a greater stabilizing effect than the same size weight mounted closer to the surface.
An instrument cage mounted to the buoy frame helps to stabilize the buoy and provides a deeper location for mounting additional weight. For single-point mooring configurations, mooring chain and lines connected to the bottom of the cage may provide adequate ballast. For multi-point configurations, the mooring hardware does not contribute to the ballast weight.
Before deploying a buoy system, some experimentation may be required to properly balance the system. If needed, add ½ inch chain (~2.3lb/ft) to the bottom of the cage. Figure 1 shows an example of a buoy system with a short section of chain added. NexSens also manufactures a 25 lb ballast weight that can be added to the cage in some applications. Contact NexSens for more information.
CB-series buoy data wells are not rated for submersion, so proper ballast weight is critical to ensure that the buoy does not overturn, including when subjected to additional loading (e.g. high wind/waves, periodic snow/ice loads, etc.).