Taken from a different vantage point the structure is seen from the stern. The waves
hitting the structure are more visible now. The roll stability can be seen to be
good from this angle. This video is taken later in the day of the storm when the
visibility was excellent.
Note in all the videos that the structure, being moored on a single point mooring
is aligning well with the wind and waves. On previous models there were secondary
swells from reflected waves off the cliffs. This produced roll movement. On this
version of the semi-submersible the structure did not seem affected by any roll.
Fishguard does have quite a large tidal flow, however, during the storm this did
not affect the performance of the structure.
The 1-15 scale model was launched in March 2010. During the trial it survived a storm
passing NW of Fishguard. The wind strength was possibly less than needed, but the
sea state was producing 1.8m wave whereas the structure was only expected to work
in 1m waves. You cannot control the weather!. So the heave and surge on the video
above was much greater than that expected. The period of the sea waves was 6 seconds,
so the depth of the waves was well in excess of the structure’s draught and the depth
of water, (12m), hence the heave was about 30%-40% of the wave height. The surge
was due to elasticity in the mooring rope, which could be largely inhibited by using
a stiffer type mooring rope or even a cable or chain. The videos shows the structure
from the beam and shows it’s excellent pitching stability.
The first section of this video has a period of smaller waves. The structural movement
is limited as would be the case if these waves were the right height for the scale
of the model.
Additional footage. Poor visibility. Large movement in the peak of the storm. Waves
were 2x the height designed for.