Analyses of Multiple-Float-Supported Platforms in Waves 



The 210 float elements were made of plexiglas tube and sheet accord- 

 ing to the sketch shown in Figure 44. Solvent -bonding was used to as- 

 semble the parts in a watertight fashion. 



The float elements were connected in sets of 6 to an aluminum 

 channel. The channel was lightened considerably by drilling holes and 

 the tubes were ballasted with brass weights and lead shot so that a row 

 floated at the correct draft and roll angle, with a small positive roll 

 stability. This was checked by floating the sets in a fish tank while 

 lightly restraining them against pitching (the rows are very unstable 

 in pitch). 



The rows are connected to each other by linkages consisting of 

 3-3/4"x l/2"x0.050" aluminum strips with 1/8" diameter reamed 

 holes spaced 3-1/4" center-to-center. The linages roll on 0.1245 

 diameter x 1/8" long shoulder screws which are secured to light posts 

 at the ends of the rows of floats. The vertical spacing of the linkages 

 is 4 inches. The float are arranged in an equilateral triangular fashion, 

 as indicated in the sketch of Figure 45. 



Although roll stability of the articulated model is present be- 

 cause each row is suitably ballasted, the pitch behavior is unstable 

 because each row is unstable and the 4 -bar-linkage connections provide 

 no restraint unless one row is held so that it can move only vertically. 

 The center row (number 18) was restrained by a vertical tube which 

 slides in a pair of linear-motion ball bearings, as indicated in the 

 sketch of Figure 46. 



The linear motion bearing is secured to a light weight (approxi- 

 mately 3 lbs) carriage which rides on low-friction wheels on a mono- 

 rail about 12 inches avove the water, permitting effective freedom of 

 surge. 



The vertical motions of five locations along the lenght of the 

 model, at rows 1,9, 18,27 and 35, were measured by systems consist- 

 ing of a long (approximately 8 ft) vertical string between the measure- 

 ment point on the model and quadrant connected to the shaft of a rotary 

 variable differential transformer (RVDT). These RVDT's have very 

 low friction ball bearings and the quadrants are very slightly counter- 

 balanced to assure that the string remains in tension. 



Motions tests were carried out in November 1971 in Davidson 

 Laboratory Tank No. 3, which is 300-ft long, 12-ft wide and 6-ft deep. 



Additional tests were carried out in June 1972 in DL Tank No. 2, 

 which is 75 -ft long, 75-ft wide and 4. 5 -ft deep, to check whether tank 



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