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02 October 2010

 

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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.

 

VIDEOS

 

 

 

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.