Sir Isaac Newton’s First Law of Motion
states that an object at rest tends to stay at rest and that
an object in motion tends to stay in motion with the same speed
and in the same direction unless acted upon by an unbalanced
force. During a mission rehearsal exercise at the Joint Multinational
Readiness Center in Hohenfels, Germany, I observed that Soldiers
did not adequately secure vehicle loads to accommodate Newton’s
First Law of Motion.
This article is not intended to replace existing technical
manuals as a source of information for securing vehicles but
to provide leaders and drivers with basic, science-based information
and to direct them to examples of proper vehicle tiedowns using
chain and ratchet load-binders. This article will look at securing
one specific item of equipment, the All Terrain Lifter Army
System (ATLAS), a variable-reach, rough-terrain, 10,000-pound
lift-capacity forklift (VRRTFL), with a gross vehicle weight
of 33,500 pounds.
Why Does It Matter?
In science, laws are events that do not vary; they remain constantly
true. Such physical laws are important for us to know so that
we do not damage equipment and, more importantly, so that we
do not injure or kill Soldiers.
Army equipment is often heavy and bulky. While military vehicles
may seem to travel slowly, if we convert speeds measured in
miles per hour to speeds measured in feet per second, suddenly
things seem to be moving more quickly than we might have first
suspected. A vehicle moving 30 miles per hour is actually traveling
44 feet every second. Couple speed with Newton’s Laws,
and we find that items on a moving vehicle that appear to be
at rest and motionless are not motionless at all. These items
move at the same speed as the vehicle moves. This factor is
not so important when the driver and vehicle accelerate smoothly,
but it becomes highly critical when the driver, vehicle, and
load make a sudden stop. Newton more precisely stated that,
when objects are in motion, they will continue to move in the
same direction and at the same speed, unless some other force—friction,
tiedown chains, or some similar force—acts upon them
to retard or stop their movement.
So, if we have an ATLAS riding on an M172A1 low-bed trailer,
we must have something very strong to hold it to the trailer
in the event that the truck and trailer suddenly stop. If we
do not have the forklift well secured, its 33,500 pounds of
mass may continue to move forward at the speed it was traveling
before the sudden stopping force acted upon the truck, the
trailer, and the load. During such sudden stops, cargo loads
will continue to move, and the force needed to restrain those
cargo loads, depending on their speed, can be many times greater
than their normal motionless weight. This force is expressed
as g-force—the increasing force of gravity on an item
as the item accelerates.
Visualize traveling within a convoy down a
snow-covered tank trail in a 5-ton tractor towing a
low-bed trailer with an ATLAS on it. The convoy speed is a
modest 15 miles per hour (22 feet per second). Suddenly, you
hit a patch of ice, which instantly causes you to lose control
of your truck, and the truck hits a large tree, which very
rapidly brings everything to an instant and grinding halt.
What is happening behind the tractor on that trailer with the
33,500-pound ATLAS? A moment ago, you were moving along smoothly
at a modest speed, and now you are going 0 feet per second.
What speed is the forklift going? Did it stop with you? Did
it continue to travel along at some speed between 22 and 0
feet per second? What is going to stop the forklift? Will it
stop before it goes through the cab of your tractor? Do you
have sufficiently strong chains in the proper quantities to
hold the ATLAS stationary on the trailer? Do your chains have
the needed excess safety capacity? The only thing that is going
to stop that forklift mounted on a trailer is to have properly
attached restraints of the appropriate size and strength. So,
just how should you position the chain assemblies in order
to tame this beast?
Chains and Load Binders
A careful examination of the current ATLAS technical manual
(TM), TM 10–3930–673–10, incorrectly illustrates
the chain used in the tiedown illustration as 0.38-inch chain
having a 9,000-pound capacity working load limit (WLL). The
manual’s sample problem uses a -inch
railroad-only chain having a WLL of 13,750 pounds. These chains,
both the -inch, 9,000-pound WLL and
13,750-pound WLL, are commercially available, but they are
not readily identifiable as being available within the Defense
Logistics Agency supply system for use with truck transportation.
Both are railroad chains, and both are very expensive.
An ATLAS vehicle has 12 tiedown points, each rated at 13,300
pounds. The TM’s example uses a total of eight chains,
four restraining forward motion and four restraining aft motion;
all chains work to restrain lateral motion and exert force
to preclude vertical motion. Many methods can be used to secure
a vehicle correctly, but remember that these computations do
not fully consider more aggressive driving conditions that
are possible in tactical or combat environments. Because the
manual’s authors computed the requirement using Army
standards made obsolete with the implementation of 49 CFR (Code
of Federal Regulations) 393.102 on 1 January 2004, their answer
provides a quantity of chains that does not satisfy current
To get the correct answer, use the U.S. Department
of Transportation (DOT) column of the restraint table above.
If you use grade
70 steel transport chains,-inch
with a WLL of 6,600 pounds, you must use a minimum of 17
to restrain forward motion, 6 to restrain aft motion, and
1 to restrain the forklift’s
boom and fork assembly. These quantities (less the boom-securing
chain) were determined by using the TACOM Life Cycle Management
Command formula with a modified rounding rule (illustrated
at right). We will need several more chains than the TM reflects.
Always round up any fractions to the next even whole number
of chains, and maintain symmetry (balance) in your tiedowns.
The load needs an equal number of chains on each side (left
and right) of the load and the trailer.
When computing the chain requirements, you may use the relatively
simple but multistep formula found in TM 10–3930–673–10. It
yields good estimates that are conservatively safe. Using
this formula, you can change your restraint factors, chain
size, and strengths and compute the number of chains you
will need for most conditions you may encounter. The formula
also permits you to compute requirements based on the chains
you have available for a particular load-carrying vehicle.
The solution in the sidebar provides the calculation for
chain with a WLL of 6,600 pounds (see table below). It is
important that you not attempt direct comparisons of the
factors between the various transport modes
listed in the table at right because the safety factors and
restraint design requirements differ between those modes.
Chain standards vary widely within the Department of Defense
and industry. To ensure that you have the correct chains on
hand, you need to check the types and condition of your chains
early, before it is time to move your vehicles and your cargo.
If your unit receives a trailer through a lateral transfer,
ensure that you have the correct size and quantity of basic
issue “transport chains” and that the chains are
serviceable. Otherwise, your unit may end up without the correct
chains and will have to buy the correct chains with its limited
mission funds. While waiting for those chains to arrive, you
will not be able to perform your mission. These chains are
absolutely essential to the readiness of the trailer and, in
turn, your unit.
For transportation load-securing purposes, the industry standard
is grade 70 welded, high-strength, carbon-steel chain. Grade
70 chain with links of -inch and larger will, at some periodic
link interval (usually one link in every 36 inches of chain),
have an embossed (raised) mark of either a 7, 70, or 700, and
the chain also will have a manufacturer’s identification
symbol or mark. Grade 80 chain has marks of 8, 80, or 800,
and grade 100 chain has a mark of 10, 100, or 1,000. Grades
80 and 100 chains are both high-strength, steel-alloy chains.
Some chain customers (such as the U.S. Government) may dictate
specific color coding and finishing for chains of certain sizes
As a rule, use only chains you can identify by national stock
number (NSN) and that match your TM’s basic issue items
or additional authorized item lists. If you cannot identify
a chain’s NSN or determine by its grade that it meets
Federal specifications, do not use it unless you compute the
chain’s restraint factor based on grade 30 proof coil
chain—a weak grade of chain.
If a chain shows signs of damage, do not use it! Turn it in
to your supply room immediately, and order new chain. What
constitutes a damaged chain? Any chain with bent, broken, chipped,
cracked, crushed, elongated (stretched), gouged, or twisted
links; links having excessively worn bearing surfaces (grooved—inside
the individual links); or a chain with a knot in it is a damaged
chain. If a chain has grab hooks or other devices on the end,
and those items are damaged, the entire chain assembly is unserviceable.
You can gain greater restraint in several ways. You may use more chains, stronger
chains, or larger chains, or combine all three. You also can recalculate the
number of chains needed by changing the number of g-forces that you believe you
want to restrain and then applying the resultant number of chains. You also may
apply chains at more efficient angles to gain better balance between the restraints
provided in each direction and minimize the number of chains required. Never
exceed the tiedown anchor capacities for either the cargo load or the tiedown
anchors on the trailer or cargo bed. All chain angles should be between 30 and
45 degrees from the horizontal deck.
Securing the Chains
Each -inch restraining chain needs a load binder (NSN 3990–01–440–5975).
This load binder is stronger than the -inch chain. Always ensure that the strength
of the load binder and its attached chains and grab hooks is equal to or greater
than the strength of the rest of your securement system. Two of the forward and
two of the aft restraining chains must crisscross. Those chains must go from
tiedown anchors on the left side of the forklift to the right side of the trailer
and from the right side of the forklift to the left side of the trailer. This
provides adequate lateral restraint.
The remaining forward restraining chains go from the ATLAS’s tiedown anchors
directly to a side anchor point on the trailer at a 30- to 45-degree angle. You
want to form two 30- to 45-degree angles. The first should be between the longitudinal
axis (the forward and aft line) of the vehicle and the tied-down vehicle’s
anchor point. The second should be between the tied down vehicle’s tiedown
anchor and the (imaginary) perpendicular (90-degree) angle to the side of the
bed on the cargo-carrying vehicle’s side. (This is the lateral component.)
These tiedowns provide restraint in the longitudinal, lateral, and vertical dimensions.
(See drawing below.)
When combined, the two 45-degree angles reduce
the effective restraint provided by any chain by half its rated
WLL in any of the three directions. With -inch
chain, each 6,600-pound chain’s effective restraint becomes only 3,300
pounds. That is quite a decrease! As we change a chain’s angle, the effective
restraint ability of the chain changes as well. (These angular changes have
no effect on the actual WLL of the chain.) The technical manual for the ATLAS
us to assume 45-degree angles.
Although these numbers sound large and impressive, this tiedown plan is only
designed to restrain the secured vehicle in the event of “heavy or panic
braking” by the load-carrying vehicle. It includes no substantial restraint
buffer to guarantee the load will stay on the trailer under more violent conditions.
(Granted, although there is a difference between the WLL of a chain or load
binder, its proof test, and the minimum breaking strength of a chain, you are
to use any factors except the WLL when planning and physically securing your
load according to the criteria of the table below). However, by rounding
up to the nearest even whole number of chains, we add more security to our
load. The 17th chain serves only to secure the boom and forks from telescoping
under severe acceleration.
Drivers, noncommissioned officers (NCOs), and officers must
make responsible, informed risk assessments to mitigate the
risks posed by moving heavy loads on wheeled vehicles. They
must continuously consider road and weather conditions, convoy
speeds, and drivers’ experience. Fewer
-inch, grade 70
transport chains may hold an ATLAS while panic breaking under
otherwise ideal driving conditions to the satisfaction of the
DOT or the Army’s Transportation Engineering Agency (TEA).
However, fewer chains may not completely secure the load under
more adverse field conditions or during even a minor accident.
Load binders apply tension to the chains. Tension is critical
to maximizing the available strength of a chain. Loose chains
do not secure a load; they permit the load to shift, which
is something you definitely do not want to happen. Further,
when a loose chain suddenly becomes taught under extreme acceleration,
the tension may exceed the chains’ and the load binders’ WLLs
and, quite possibly, even their minimum breaking limits. Drivers
must ensure that each load binder closely matches the strength
and size of its chain. Any load’s stability will only
have the strength of the weakest link among the tiedown anchors,
chains, and load binders.
Transport chains are not lightweight chains. Each link is made
from linked steel or steel alloy rod; the named size is the
measurement of the diameter of the metal rod that forms its
links. Pick up a ruler and look at how thick these chain links
are. Whether -,
-, or -inch, these are not
discount store bicycle-locking chains. You can find more information
on what the various tiedowns and their component elements should
look like in the Military Traffic Management Command Transportation
Engineering Agency (MTMCTEA) Pamphlet 55–20, Tiedown
Handbook for Truck Movements. However, in doing so, exercise
great caution when looking at chain strengths and sizes. A
chain’s strength—its WLL—is a function of
its size and grade rating (the type of metal and manufacturing
process used in forming the metal chain). Consult the Welded
Steel Chain Specifications published by the National Association
of Chain Manufacturers and the Federal Specification RR–C–271D,
Chains and Attachments, Welded and Weldless, for accurate information
on the standard size and strengths of chain.
Ratchet-type load binders are preferable to levered
load binders. Ratchet load binders are much safer devices for
operators to use. If operators and supervisors must use levered
load binders, they must ensure that all levered load binders
have safety lacing wire to safety-seal all load binder levers.
Drivers cannot simply wrap chain around the lever and hope
the chain stays in place. Although some drivers do this in
the field, it is not a correct technique for securing the levered
load binder; you must use the lacing wire to secure the lever.
Without using the safety lacing wire to secure the load binder,
your chain could come unwrapped from around the lever and become
loose while you drive down the road. You definitely do not
want a load binder to come loose and release a portion of your
load. Check the security of your loads on a regular basis—initially,
before you leave your motor park; again, within the first 2
miles of leaving the motor park; and then check load security
at every rest halt.
Improving Highway Transportation Standards
The Army’s manuals have been requiring fewer chains than
the newest DOT standards require for commercial vehicles driving
on U.S. highways. Army manuals should be corrected to align
with DOT Federal Motor Carrier Safety Administration Rules
and Regulations, 49 CFR, Parts 392 and 393. The Army, at the
very least, should use the minimum standards of the DOT highway
factors. Yet, is this the best practice for our operators and
our equipment? Is it reasonable to assume that field and tactical
driving conditions may easily exceed commercial trucking conditions?
The Army needs to consider doing three things to improve highway
transportation load securement. First, use no less than the
DOT restraint factor
standards with the TACOM formula provided in the ATLAS TM.
This computation provides greater restraint than the TEA figures
do, which will provide drivers with greater protection and
better protect valuable equipment from coming loose in the
event of accidents, even relatively minor ones. Second, change
the doctrine in Field Manual 55–30, Army Transport Units
and Operations, which states that the shipping units provide
the tiedown devices. Units no longer do this, so it should
be removed from Army doctrine. Transportation units should
carry chains on board their trailers in sufficient sizes and
quantities to tie down properly any load that they are authorized
to move. This will be cheaper than having every unit in the
Army purchase chains for all of the vehicles that they might
need to move. Third, standardize the size of motor transport
chains. Chains much larger than
inch are too difficult for many Soldiers to handle.
The rail industry uses - and
-inch chains; this would
probably be smart for the Army to do. Grade 70 transport chain
provides the best overall value. Although higher grades of
the same sized chain are stronger, their costs rise more steeply
than any corresponding increases in strength.
Unfortunately, within the Army, we continue to have accidents. If you want a
greater level of security and safety, you need to consider increasing the size
or the number, or both, of the chains and load binders you use to secure your
loads against forward motion to levels beyond a mere 0.8 g!
Newton’s First Law of Motion is a law we must understand and live with
everyday. Drivers, NCOs, and commissioned officers must fully understand the
realities of moving heavy cargo on Army trucks and trailers. It is virtually
impossible to secure the heaviest truck loads against every conceivable crash
scenario. We need to secure our loads against reasonable driving conditions and
risks using the WLLs of our transportation chains, but we definitely need to
exceed the minimum standards listed by both DOT and TEA. Their figures are simply
too low to adequately protect Soldiers and cargo in more rigorous conditions.
This is primarily because DOT regulations have changed and because the calculations
are based on heavy breaking in fair weather conditions. However, we all must
drive safely and securely, whether in combat, the field, or on the highway.
Colonel Neal H. Bralley, USA (Ret.), is an assistant professor of logistics
and force management at the Army Command and General Staff College at Fort Leavenworth,
Kansas. A graduate of the Army Command and General Staff College and the Naval
War College, he served in numerous command and staff positions in Korea, Germany,
Saudi Arabia, and the United States.