Where F_ = tractive effort (lb) 



W = vehicle weight (lb) 



()) = friction angle 



A = contact area (in. ) 



2 

 c = cohesive index, S (lb /in. ) 



For the target weight of 20,000 pounds dry (17,300 pounds wet), and an 

 allowable ground bearing pressure of 2 psi, the contact area can be found 

 as: 



W 2 



A = — = 8,650 in. 



2 psi 



Therefore, the tractive force is: 



Sand: (f) = 30°, c = 



F^ = 17,300 tan 30° = 10,000 lb 



Clay: <}. = 0, c^^^^^^^ :x, 1 psi 

 F^ = 8,650 lb 



These are theoretical and, probably, optimistic values. Also, typi'-.al 

 seafloor soils are not uniformly clay or sand, and the effect of water, 

 ground bearing pressure, sinkage, and slippage has not been established 

 for seafloor application. Nevertheless, these values are in the range that 

 an improved cable burial system will be operating. In Reference 43, two 

 vehicle types (6x6 wheeled, and two -tracked conventional) were shown 

 to be possible configurations for a seafloor-crawling work vehicle. 



Another configuration for a mobile vehicle, a screw-wheel concept, 

 was studied in detail in Reference 44. A screw-wheel configuration is 

 basically an Archimedes screw with the blades arranged in a helix around 

 a cylinder. This device has been shown quite effective in ''screwing'' 

 its way through water and marshy soils, but suffers from extreme friction 

 losses in sand. For the configuration discussed in Reference 44, four 

 screw-wheels are installed such that they can orient to operate in the 

 screw modes (for clays) , or turn 90 degrees to operate in a wheel mode 

 (for sands). Intermediate materials may require intermediate (hence, 

 screw-wheel) settings. 



Propelling a cable burier with tracks, wheels, or screw-wheels is 

 particularly attractive in that the machine may be accurately controlled, 

 either remotely or automatically, to follow the cable and avoid obstacles, 

 or even in a search mode to find the cable which is to be buried. These 

 vehicles also can climb slopes, climb obstacles, and control their speed 

 to match the soil and terrain conditions. The most obvious disadvantage 

 is that this type of propulsion system depends on the soil characteristics 



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