Analyses of Multiple-Float-Supported Platforms in Waves 



of floats from one up. Single float platforms, such as the SPAR and 

 FLIP research vehicles will not, however, be considered here. Only- 

 three and four-float supported platforms, applicable to air-sea craft, 

 are treated in this report. The four -float configurations are arranged 

 so that two of the floats support the main hull, and carry most of the 

 weight while the other two floats are attached to the wings, producing 

 a cruciform array. For the three -float configurations, all floats are 

 of equal size in an equilateral triangular array. 



The total displaced volume of the floats must equal the vehicle' 

 s weight and static pitch and roll stability must be provided. Static 

 stability criteria usually follow naval architectural practice, measur- 

 ing stability by metacentric height. From this consideration then, the 

 float slenderness (waterplane area) and spacing are related to the ver- 

 tical center of gravity of the craft. 



Descriptions of the elementary fundamentals of the dynamic 

 motions response of vertical float and "semi-submersible" platforms 

 have been outlined by Barr [6 J , Julien and Carrive [7 J > an d most 

 recently and thoroughly by Hooft [8]. Considerations both of natural 

 frequencies and of minimization of wave excitation forces and/or 

 moments are of key importance in this regard. A more complete quan- 

 titative description of these considerations for heaving motions of 

 isolated floats is given in the present paper as part of the discussion 

 of the performance of closely-packed arrays of floats. 



DESCRIPTIONS OF MODELS 



Tests in irregular seas were conducted with variations of two 

 basic model configurations. One represents a cruciform array of floats 

 where two equal floats would attach to the aircraft fuselage and two to 

 the wings. This type of system was investigated by Ling-Temco-Vought 

 [9] for application to the XC-124A VTOL aircraft and by General 

 Dynamic s/Convair [lOJ for application to the P5A seaplane equipped 

 with hydro-skis. The second configuration uses three equal floats in 

 a triangular pattern. Such an arrangement has been planned by Boeing- 

 Vertol [ll] for application to the CH-46A helicopter. 



Sketches illustrating the two basic configurations tested are 

 shown in Figures 1 and 2. The basic frames, to which the floats are 

 attached, are made of aluminum in a lightweight but rigid construc- 

 tion. The floats, which are interchangeable and have adjustable spac- 

 ings, are made of low density (2 lbs per cu ft) closed-cell sytrofoam 

 with l/8-in thick aliminum plates on top to facilitate securing to the 

 frame. All floats used have a circular cylindrical body shape with a 



797 



