Price and Compare Vehicles: Certain dangers are
inherent in off roading as with any other sport. Vehicle accidents (such as roll
overs), equipment failures, and environmental conditions can all work against
our trying to maintain 98.6 degrees (also know as life). Winching a stuck or
disabled vehicle should be considered one of the inherent dangers associated
with our sport. Educating yourself on, what I call, "Winchology" can greatly
reduce the hazards associated with winching and minimize the strain placed on
vehicle components. I am assuming you have read you winch owner's manual and
have some knowledge of winching. This column reflects winch employment
techniques I have developed based upon my study of current periodicals,
corporate literature, and college physics. If you have a personal technique, or
have dissenting technical views, I welcome dialog so lessons can be
disseminated. Shortly after
purchasing my first winch and snatch block I began to wonder where these
tremendous forces were being applied that are able to free a stuck vehicle. (I
will not digress into which winch to buy for your application. Four wheel drive
magazines often compare winch capabilities since manufactures buy advertising
space. I tend to go with the school of thought that says, "buy the biggest winch
you can afford.") The manufacturer rated my winch at 8,000 lbs single line pull
(i.e. running the line from my jeep directly to an anchor) when all the cable is
spooled out to the last layer on the drum. Let me stop here and explain. Each
time a new layer of cable is wrapped around the drum, the winch's pull capacity
is reduced proportionally to the relative increase in drum diameter. To
visualize this, see your drum as a certain diameter gear, say 2 inches. Using
5/16 inch cable, each time a new wrap starts, you have increased the "gear's"
diameter 10/16 inch or .625 inch Dividing .625 by the gears original 2 inch
diameter yields a 31% increase in gear size. This is a bad thing. Increasing
gear size means less torque and effective pulling power. This is why
manufacturers rate their winches with one spool on the drum and why you want the
most cable off the drum to maximize your pulling capability. With this
information tucked in the back of my mind, I returned to my most puzzling
concern of using the snatch block to double the pulling power. The 5/6 inch
cable supplied with the winch was rated at 9,000lbs, the winch can pull
8,000lbs, and using the snatch block gives the potential to pull 16,000lbs. Wait
a minute. The cable is only good for 9,000lbs and I could be pulling 16,000lbs!
Where is the 16,000lbs being applied? Figure 1 depicts a typical winch and
snatch block rigging with load distribution. As you can see, all
components attached to the anchor (tree) end must be capable of withstanding
16,000lbs of force. Your truck's front bumper/winch mount must also be able to
withstand 16,000lbs if you attach the winch hook to a component tied to the
winch mount. If in doubt, attach the winch hook to a point farther back on the
frame. The snatch block configured in this manner creates a mechanical advantage
(MI) equal to the output Force (Fo), over the input force (FI) or MI = Fo / FI.
The MI is only
applied if the winch hook is attached to your vehicle. If the winch hook were
attached to another anchor, Fo and FI would equal 8,000lbs in our example. A
snatch block employed in this manner serves to change the direction of the input
force. Knowing how to get
the most out of your winch and knowing where the load is applied, can mean the
difference between a safe efficient rigging and a fatal accident. Note where the
force is applied, and ensure those components have that working capacity. A good
quality clevis will have the working load stamped on it; if yours does not, (it
may say made in China and have no rating information) it's rating should be
questioned. Naturally, the fewer components you include in your rigging, the
less potential to have a weak link. Reducing the forces placed on your
components can also eliminate potentially weak links. The winch mount may
be a weak link you can protect. Lets say you are in a situation where you have a
poor vehicle weight ratio (your truck is being dragged toward a vehicle you are
trying to recover). Strapping your truck to a suitable anchor behind you or
placing the front of the winch mount (not necessarily the bumper) against a
tree/rock, can create a better weight ratio. however, both these techniques have
damaging potential. If your front bumper/winch mount is not sufficiently strong
or the vehicle shifts, you may damage the front of your vehicle. Anchoring your
vehicle from behind while winching the heavier vehicle may damage the vehicle's
frame. I am especially reluctant to perform this technique since my Cherokee has
unibody construction (ugly thought isn't it). If you need to strap to a anchor
behind you, consider running the strap under your truck and attaching it to the
winch mount. In essence, you have mounted your winch to a tree using a strap.
This will eliminate the force placed on the truck's chassis and reduce the force
placed on the winch mount. So far, our
winching examples have assumed a straight pull. What happens when you begin
winching at angles? Simple (not) multiply FI (8,000lbs) times the Cosine of the
angle to the anchor. For a 45 degree angle, that means 8,000 X .707 reducing
your effective force to 5656lbs. Also, your winch mount was designed for
straight pulls meaning it may not withstand the torsional forces applied when
angle winching. Simply put, get as straight in line as possible with the anchor
or stuck vehicle when winching. Follow us on Twitter at www.twitter.com/OffRoadDotCom
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