Q2 Z2,(Q2) Z2(Q2) - Institute for Water Resources - U.S. Army

A final note concerning the effect of stream velocity on pre-
dicted acceleration and deceleration times and distances is in order.
If a constant velocity of water flow, S w , is assumed, a tow beginning
to accelerate upstream will at time t = 0 be operating at a velocity
equal to the negative of the stream current, -Sw . If the tow's full
speed in still water is V f , then its attainable speed for the upstream
movement is V f - S w . If it is assumed that no changes occur in the
resistance and push functions and that .stream current only affects
the tow's speed additively, then the tow will require the same time
to accelerate from v = -
S
w
to v = V - S as it will to accelerate
f w
from v = 0 to v = V f . The same reasoning applies mutatis mutandis
for downstream acceleration, and similar arguments for both situations
may be made for the case of deceleration. Therefore, stream current
may be ignored in considering time required and distance traveled in
acceleration and deceleration of barge tows.
Note on Calculation of Mass. For the computation of accelera-
tion time, the mass of the tow is required. Mass is.defined as weight
divided by gravity: m = wig. The quantity k is usually approximated.
as 32 feet/second 2 . Since the tow speed is in units of miles per hour
(mph), the units of g must be altered in order to achieve the requisite
dimensionality of acceleration time. Specifically, if these times are
to be in minutes (min.). then g = 1309 mph/min.; in hours (hr.), g =
78,540 mph/hr.
The other component of mass is weight. The gross weight of the
entire tow is required. The cargo weight of a barge is a function of
its draft, and capacity tables exist from which one can determine the
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