Of the track systems, the low-ground-pressure pontoon with a ladder 
grouser system is predicted to be the most successful, and will be functional 
on all but rocky bottoms. Ground pressure can easily be adjusted to the soil 
conditions using buoyancy. 
During the preparation of this report, a single test track conforming 
to the conditions listed in the summary was designed and fabricated; the 
schematic from the contract proposal is shown in Figure 40. 
stainless skid plate, track guide and ballast tray adjustable height drawbar 
optional: Teflon or Tem-PR-Glas tape 
forced water lubrication 
Figure 40. Experimental test track with water lubricated rubber belt sliding on 
stainless steel skid plate (Nuttall, 1970). 
The actual equipment is shown in Figure 41, suspended prior to tests 
in shallow water of Chesapeake Bay, Maryland. Results of these early tests 
are described in Nuttall (1970a) and in Nuttall (1970b). The unit is being 
tested extensively in submerged bottom materials by the Naval Civil Engi- 
neering Laboratory, with results expected to be published in a technical 
report by or before mid-1971. Preliminary analysis of results indicates 
that for bottoms other than sand, the maximum traction that can be 
achieved can be developed at low ground pressures and essentially zero 
slip, and that higher pressures and greater slip than these minimum values 
tend to destroy the structure of the bottom material. The tracks then dig 
in rapidly, an undesirable consequence. The cleated track is carried on a 
rubber belt which is in contact with the smooth steel bottom. A novel 
feature of this design is that water can be forced under low pressure 
between the track and the belt, resulting in a very low friction. The 
unit, hydraulically powered, is to be tested in a variety of conditions 
including shallow water in muds, sands, and loose sediments. Provision 
is made for adjusting the ground pressure and measuring the drawbar pull 
developed. Optimum use of buoyancy to adjust the total ground pressure 
will be incorporated in the final designs. 
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