HEAVY-LIFT BOTTOM CRAWLER 



At the outset of the present study, two design approaches seemed 

 promising for conceptualizing a feasible bottom crawler with a 20-ton lift 

 capacity. One, a tracked or wheeled vehicle with personnel sphere, lifting 

 gear, power, and propulsion system, would depend on counterweight (or 

 other restraint) to balance the load overturning moment. This design would 

 incorporate a crane, A-frame, or fork lift at the forward end and a fixed (or 

 jettisonable) counterweight at the rear. This concept, however, was found 

 impractical for many potential sea floor construction sites. Pelagic soils are 

 typically soft, oozy sediments with minimal bearing strength. Preliminary 

 analysis showed that a bottom crawling vehicle, weighing at least 20 tons and 

 equipped with any one of several wheel and track configurations, simply 

 could not manuever in soft ocean sediments. 



Another approach was considered whereby the vehicle would be 

 designed to have near neutral buoyancy at all times while operating on the 

 ocean floor. After securing the load, a deballasting system would provide 

 the increased lift needed to make the vehicle/load system once again near 

 neutral buoyancy. Actually, the vehicle would probably operate in a 

 slightly negative buoyant state in order that it remain affixed to the bottom. 

 Powered, cleated wheels or tracks would provide the needed tractive force. 



Several disadvantages of the foregoing concept can be enumerated. 

 First, the vehicle is likely to be a greater consumer of power than competing 

 systems such as the heavy-lift submersible previously discussed. A bottom 

 crawling vehicle is likely to stir-up sediments, possibly obscuring and quickly 

 bringing to a halt any prolonged underwater construction projects. There 

 is also an ever present danger of getting stuck in the ooze and having to abort 

 the mission, risking both the vehicle and its human occupants. Lastly, the 

 variable deballasting crawler is little more than a heavy-lift submersible in 

 disguise, albeit a more heavily powered submersible with wheels or tracks 

 attached to its undercarriage. Although the crawler has some of the advan- 

 tages offered by the pure submersible, it also has many more operational 

 disadvantages. The latter are largely a result of the crawlers necessary contact 

 with the ocean floor. 



The authors see no point in considering a bottom crawling vehicle as 

 a serious NBTS candidate. They are not implying, however, that bottom 

 crawlers have no role in undersea construction. Possible applications for 

 bottom crawling vehicles might include: 



1 . Exploratory vehicles for testing sediments and mapping bottom 

 topography. 



2. Trenchers and dredgers for laying power and utility lines. 



81 



