McClure and Hove 



the later tests. For the resistance and moment tests the model was fitted with 

 elliptical cross-section braces instead of circular members. Also damping 

 tanks were not present. The data given in Figs. 2, 3, and 4 of the basic paper 

 are not corrected for these additions, but the data used in the positioning ma- 

 neuvers analysis have been appropriately increased. The shallow draft maneu- 

 vering tests were conducted earlier and in addition to the above changes the 

 lower hulls were 20 feet shorter or 370 feet long and were 10 feet closer together. 



Appendix B 

 POSITIONING UNIT, PROPELLER, AND NOZZLE 



The drilling platform has six positioning units, one located in each of the 

 platform's stability columns. Each unit consists of a 1000-HP DC motor in- 

 stalled in the lower hull gland, and an external assembly consisting of double 

 right-angle gears, training assembly, housing, propeller, nozzle, and supporting 

 struts (Fig, Bl). The external assembly can be withdrawn or installed while the 

 platform is in operation through the positioning unit trunk extending from the 

 upper deck of the platform through the lower hulls. The flange of the position- 

 ing unit assembly rests on a mating flange and the trunk and inflatable seals en- 

 able the trunk to be kept dry during normal operation. The unit is steered by a 

 reversible AC motor and worm gear drive. It can be rotated continuously in 

 either direction at 2 rpm. The external assembly contains its own built-in 

 lubricating system and is pressurized to minimize risk of leakage. 



Installation of the units is accomplished by lowering the external unit into 

 the trunk using one of the platform's deck cranes or a portable positioning unit 

 handling fixture. The unit is seated on the seating flange in the trunk and the six 

 hold-down latches are set. The inflatable seals are then actuated and de- 

 watering begun, utilizing the platform's ballasting pumping system. With de- 

 watering complete, a mechanic enters the trunk, removes the watertight covers 

 over the drive shaft and the electric lead couplings and makes these up using 

 short connecting pieces. The unit is then ready for check out and operation. 

 Removal follows the same procedure in reverse. 



The propellers and nozzles were designed in accordance with procedures 

 given by van Manen.* The propeller was based on van Manen's K 4-55 series. 

 With the deep submergence of the propellers while operating, it has been possi- 

 ble to reduce the blade width without danger of cavitation. The nozzle is a mod- 

 ified van Manen No. 18 profile. The incidence angle was increased from 10.2 to 

 11.7 degrees to compensate for the tapered nacelle and propeller hub. 



J. D. van Manen and A. Superina, "The Design of Screw Propellers in Nozzles," 

 International Shipbuilding Progress No. 55, March 1959. 



432 



