contained large amounts of free water in the top few inches, the Marsh 
Screw performed quite well, almost unaffected by the soil shear strength. 
The critical factor apparently was the friction between the soil and the 
rotors. On wet or dry sand and on sticky, water-free soft soils, the Marsh 
Screw was definitely inferior to the M29C Weasel, a tracked vehicle. 
Walking Barge. The Walking Barge was built as an amphibious cargo 
carrier and tested at NCEL shortly after World War ||. This large floating 
barge was divided longitudinally into three segments or pontoons, the center 
one with a bottom area equal to the sum of the bottom areas of the two side 
pontoons. When the barge was driven ashore and grounded, it proceeded up 
the beach by resting on the center pontoon, moving the two outside pontoons 
up, forward, and down until the weight was transferred to them. Then the 
center pontoon moved up, forward and down to complete the walking cycle. 
This was repeated to provide forward motion over the beach (Figure 38). 
At first glance, an apparent 
advantage of the walking barge was 
its large, flat bottom which provided 
a large ground contact area and low 
ground pressure. In operation, 
however, all the weight was usually 
transferred to one-half the bottom 
area, thus doubling the apparent 
ground pressure. On a sandy beach, 
this was no problem, and the barge 
moved steadily forward. 
In tests on the mud flats at 
Point Mugu, the walking barge sank 
several feet into the mud but stayed 
afloat and moved slowly forward. 
After a few dozen feet of progress, 
however, the weight-bearing surface 
sank so deep in the mud that the 
other pontoon, or pontoons, dragged 
in the mud surface on their forward 
travel; this counteracted the rearward 
Figure 38. Walking barge principle drag and caused the unit to stop its 
developed at NCEL in forward movement. |t was proposed 
early 1950's. to put hinged flaps on the bottom of 
the pontoons which would fold flat 
against the bottom during the pontoon’s forward movement and drop down 
into a vertical position during the pontoon’s stationary period to prevent 
their slipping backward. This proposal was never carried out. 
47 
