The initial step in determining C, for the three different 300-foot 
x 300-foot concepts is to consider the configuration for the buoyant 
support elements noted. In each case, the listed drafts are for (1) 
total dead load plus 25% live load, but with all unnecessary water 
ballast removed and (2) partial sections with 80% of the deck removed 
and no live load. Furthermore, it is assumed that the barge hull does 
not have highly streamlined ''ship-like'' prow and aft sections, and that 
the cylindrical elements employed in the semi-submersible and elevated 
platform have not been made more hydrodynamically efficient by envelop- 
ing them in streamlined fairings. 
Hoerner (1965) presents drag coefficient data for barge-like hulls. 
Hulls with squared-off ends and length to beam ratios of 4 to 1 have 
drag coefficients on the order of 0.9 (for this type of vessel pressure 
drag dominates drag due to fluid friction) while hulls with flat bottoms 
and rounded ends have much lower values of C., 0.30 being typical. On 
the other hand, highly efficient hull forms in high speed displacement 
craft can have C, values considerably less than 0.30. For the purposes 
of the present comparison, the MOBS barge-type hull will be assumed to 
have a drag coefficient of 0.30. 6 
For Reynolds numbers greater than 10 , the drag coefficient for a 
single, circular cylinder with its axis aligned normal to the incident 
flow is around 0.3. A matrix of cylinders, however, will be subject 
to interference effects which will probably result in a net lowering of 
the drag coefficient, especially for those cylinders in the matrix 
interior. However, since the effects of interference are difficult (if 
not impossible) to predict analytically it will be assumed herein that 
the drag coefficient for all vertical buoyant elements for both the 
elevated and semi-submersible platforms is equal to the value for a 
single, isolated cylindrical element, i. e., C, = 0.30. The horizontal 
cylindrical hulls, characteristic of the semi-submersible platform, 
are assumed to have a drag coefficient of 0.20 (See Hoerner (1965), 
Balouise Zils) ple Sin 2)\. 
Accordingly, Table 5.7 and 5.8 present the results of the drag 
estimates for the three candidates. In Table 5.8, V is the towing speed 
in knots, D is the drag force in pounds and P is the horsepower required 
to tow or propel each of the candidates. A comparison of conditions (1) 
and (2) reflect favorably on the latter to warrant further consideration. 
As a basis for towing comparison, it is noted that very large ocean- 
going tugs have about 10,000 horsepower. 
Future studies should be based on more accurate determination of 
the drag coefficients (much will depend on selection of final hull con- 
figurations) by experimentation with models in a towing tank. In addi- 
tion, wave-making drag and aerodynamic drag should be considered in 
final trade-off studies of competing systems. 
