A check will show that elastic-instability is not the critical failure mode. The 

 sphere displaces 7,230 lb of water and has a dry weight (exclusive of internal 

 furnishings and payload) of approximately 4,420 lb. The capsule payload 

 will consist of two occupants and life support and communications gear. 

 Total weight is estimated at around 1 ,000 lb. Consequently, the sphere has 

 a positive buoyancy of 7,230 -5,420= 1,810 1b. 



3. Propulsion System and Power Requirement. The submersible 

 should have an endurance of 10 hours and a cruising speed of at least 5 ft/sec. 

 The required thrust can be estimated by solving for the fluid dynamic drag 

 force 



D = Cn(VV2g)7A 



where D is the drag force, Cq is a drag coefficient, V is the vehicle velocity, 

 7 is the specific weight of the fluid medium and A is the cross-sectional area 

 of the vehicle in the direction of motion. For the case at hand 



Cq = 0.30 

 V = 5.0 ft/sec 

 7 = 64.0lb/ft^ 

 A = 73 ft^ (est) 



then D = 545 lb 



A rule of thumb suggests that a 1 hp motor and propeller delivers approximately 

 25 lb of thrust. Therefore, 545/25 = 21 .8 hp are required. Two 10 hp motors 

 will be used. Assuming 70% efficiency for the electric motors, the power 

 requirement will be 



20hp X 0.746 kw/hp x 1.30 = 19.4kw 



The total energy needed for propulsion will be 194 kw-hr. Additional stored 

 energy will be needed to power lights, telechiric devices, and miscellaneous 

 gear. This requirement is estimated at 



141 



