One modification has been introduced in
the design of the buoy, by installing the sphere at 17
instead of 18m. By this way, the distance from the center
of the sphere to the fixation of the buoy to the mooring
cable is one meter greater (the righting torque is therefore
much larger). Another modification has been introduced
in the materials used to build the upper part of the
buoy (the one equipped with arms and the instrumentation),
from aluminum to carbon composite. A specific study has
been conducted to check that this composite material
was adapted to the problem, which is definitely the case.
This study was also used for dimensioning the material
used for construction.
The impacts of these 2 changes on the upper part of
the system are: rigidity is improved, weight is diminished
by the 2/3, corrosion risks are decreased, the drag coefficient
is reduced by the use of tubes with a lower diameter,
and the elastic limit is larger than it was in comparison
to the forces imposed by breaking waves. At the end,
a net gain of 60% in the righting torque has been obtained
for the full buoy.
See here the technical note prepared before building the carbon fiber composite version