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soil – frozen vs. wet vs. dry, type of soil – clay, grass, sand,
rock, etc. - gradient of slope, adhesion factors (suction), and
weather conditions. Basically it relates to when we look under
the truck in the mud bog and state: “Shucky down Bubba,
we’re mired down good this time! Go get the tractor, JD.”
Now, back to Arizona, where getting that propane truck
unstuck from the soft, dry sand took some serious planning.
We had two vehicles with Superwinch 16.5K winches on them
that we positioned slightly apart, rigged up the ropes and set
some sand ladders (I use MAXTRAX) under the propane
truck’s rear tires to help raise the frame up off the sand as it
moved back. We also had to set a Pull-Pal to anchor one of the
winch rigs since it wanted to move toward the propane truck.
As we winched the propane truck back to terra firma we kept
alternating the MAXTRAX (we had 4) under the rear tires
which kept the heavy vehicle from sinking again. This effort
helped reduce the Mire Factor once the propane truck started
moving.
The winching effort was pretty sizeable at first since there
was a lot of dead weight to move. The Mire Factor involved the
very heavy vehicle, soft dry sand, all tires half way down on a
level surface. And let’s not forget about that darn propane tank
being full! It was a typical sunny day in the Sonoran Desert.
Once the initial pull got the vehicle rolling the winch trucks
had an easier time of it. I had the driver of the propane truck
slightly load the torque converter while in reverse gear. This
kept the drive train slightly moving but not spinning. It helped
with the lessening of the resistance.
Sometimes the initial effort to move stuck vehicles can
overpower recovery equipment if that equipment is not
specced correctly. A standard SUV that has a curb weight of
4200 pounds might require an initial effort of 8400 pounds to
get the vehicle moving. Once that vehicle starts moving it
becomes “rolling resistance” and can be as low as 1000
pounds of drag.
Factors vary on all recovery scenarios, of course. That is
why I usually recommend most winches be purchased based
on 1.5 times the gross vehicle weight as a starting point. Work
effort can be lessened by using a pulley block in the rigging.
Understanding the rating capacities of the equipment
being utilized for the rigging during any extraction operation is
ultimately important. Make sure the winch, jacks, attachment
devices and attachment points are all rated with the proper
WLL [working load limit] and have met industry standards
for Proof Testing and Design Factor conditions.
See you on the trail, ‘cause you won’t be stuck that long, right?
P
Vocabulary:
Design Factor: An industry term denoting a product’s theoretical reserve
capability usually computed by dividing the catalog ultimate load by the
WLL. Generally expressed as a ratio, e.g. 5 to 1 or 5:1; also denoted as a
Design Safety Factor.
Tackle Block: (or Block) An assembly consisting of a sheave, side plates,
and generally an end fitting. An end fitting can consist of a hook, shackle
or eye. Also known as “tackle block and sheave” assembly (herein
referred to as TB&S). Side plates may also be referred to as the “cheeks”
of the block.
Sheave or Sheave and Bearing Assembly: A wheel with a grooved
rim for wire or rope to run on while transmitting force during lifting or
hauling. Usually used to guide or change the direction of the rope or wire.
Sheaves are configured with a central hub that supports different type uses
and will be machined with a plain bore or with a bearing surface.
Plain Bore: very slow line speed, very infrequent use, low load, merely a
hole bored in the center of the sheave.
Bronze Bushing: slow line speed, moderate load, moderate use.
Roller Bearing: faster line speed, more frequent use, greater load. Comes
in tapered rollers or straight rollers machined to facilitate the shaft applicable
to the block use.
Snatch Block: A type of TB&S that allows the user to open the block to
thread the line without removing attachments on the line end. Snatch
blocks are intended for infrequent and intermittent use with slow line
speeds. Most commonly used TB&S in 4x4 vehicle recovery.
Pulley: The common or “laypersons” term for a grooved wheel. See
Sheave.
Reeving: A term used to describe the path of the rope through a system
of blocks (or one block). A reeving diagram is a pictorial rendering of the
desired path for the rope. (part of the 3 p’s)
Shackle: Industry standards dictate the use of Screw Pin Shackles which
can be used for “in-line” pulling as well as loads where “side-loading” may
occur. Side-loads will decrease the rated capacity. Never let the screw pin
rotate under “live line” while in application. There are shackles applicable
to chain, sling and general usage. Use only shackles with markings forged
into the product. Look for markings like WLL or SWL with a tonnage designation
such as: 4.75T or 6.5T. Style names like Bow or “D” are common
terms. “D” type looks like a d when held sideways. Bow types are more
rounded and more common to 4-wheelers. There are “pin” type shackles
that utilize “cir-clip” type closures. Only use Screw Pin type shackles. Size
and rating designations appropriate for the vehicle at minimal 1.5 times
the GVW.
Gross Vehicle Weight: GVW, GVWR(rating), GA(xle)WR,
C(ombined)AWR – are all applicable to helping decide how much the vehicle
might weigh when loaded. The best way is to get to a truck scale – try
a movers’ warehouse, truck stop scale, salvage yard, land fill – they will
weigh your vehicle for a few dollars. Load it up for the three day trip, kids
and dogs, cooler and gear. Then write this number with a sharpie on the
drivers door jam for future reference.
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