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www.sea-technology.com July 2014 / st 41 moored in the south position, a bigger transient was found until it stabilized to an oscillatory pattern. The study of trajectories and tensions were focused on this particular case, wherein the cable experienced the highest tension, with a maximum of about 4.6 kilone- wtons and oscillation range of 3.2 ki- lonewtons. There was a regular, circular trajec- tory of the buoy and the cable at the top. Even though it was not a periodic pattern, nor quasi-periodic, a careful study of the amplitude spectrum with the horizontal y coordinate shows "dirty" picks at a main frequency of 0.1329 at 1/7.52 hertz, inherited by the sea wave period and the corre- sponding multiples. A small frequency was also present at 0.0166 at 1/60 hertz that describes traces of the mod- ulation of 60 seconds in the temporal evolution of orbit. It is likely that traces of quasi-periodicity appear because of the physical attachment of the buoy to the chains. The range of movement of the buoy was predicted from the mod- el results, from 2.5 meters vertical am- plitude (smaller than the amplitude of the waves) and a horizontal movement in the area of 3.5 by 0.79 meters. The effect of the cable to the total ef- fective tension of the moored platform structure was the following: The am- plitude of oscillations with the cable was three times bigger than without, and the maximum value was about 2.3 times bigger. Total tension evolution was similar to the cable tension evolu- tion. The regularity of the cable trajectory contrasted with tension instabilities at every wave period. Such instabilities arose at the bottom turning point of the buoy trajectory, and the cause was the unstable chain movement. The insta- A model of the tensions at the top of the buoy. Instabilities detail total structural tension and power cable and chain tension over time. Expert small boat handlers with the strength of a National feet 800-4-SEATOW seatow.com/marine-services Boats for Hire Captains for Hire Diving Government Contracts Environmental Clean-up Transport Services Dock Work R a p i D m o B i l i z a T i o n C O M M E R C I A L S E R V I C E S M A R I N E S E R V I C E S S A LVA G E & R E C O V E RY