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Portable Backcountry Rigging Tripod

Recreation Tech Tip logo   United States Department of Agriculture Forest Service Technology & Development Program
November 2005 2300 0523-2341-MTDC

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When two tripods are needed, snatch blocks should be used to suspend the cable from the top of the tripods. The blocks reduce wear on the cable and help prevent the tripods from being pulled over as the winch pulls in cable. The wire rope cable between the tripods must always have some deflection. Post signs to warn people of the dangerous work (figure 6a) and tie flagging on rigging cables (figure 6b).

Photo of a sign warning people that work is occuring in the area.
Figures 6a and 6b--Signs should warn people about work
occurring in the area. Rigging support cables must be flagged
so workers do not trip over them or walk into them.
Photo of flags hanging from the rigging support cables to prevent workers from running into or tripping over the cables.

Tripods can lift heavy objects, but are dangerous when loads pull to the side. Crews should not attempt to pick up or drag heavy loads that are not directly under the overhead cable (figure 7). If the load is off to the side of the cable, the tripods should be moved so that the load is directly beneath the cable. Otherwise, one or both of the tripods may tip over.

Photo of a single portable tripod being used to lift the end of a log bridge.  A safety chain, labeled in the photo, is used to secure the legs of the tripod to keep them from spreading too far apart.
Figure 7--One portable tripod can be used by itself when lifting heavy
objects, such as one end of a log bridge. The safety chain around the
bottom prevents the legs from spreading too far apart. Hooks welded
near the bottom of each leg hold the chain in place.

Assembling and Setting Up the Tripods

The part numbers are shown on MTDC Drawing No. 1035 (PDF - 759 k). Before assembling a tripod, gather all the parts. Run the cable through the snatch block and choose a location where the cable can be anchored near each of the tripods.

Assembly Steps

  1. Attach the eyebolt (No. 11) to the top plate assembly (No. 7).

  2. Attach the three legs (No. 1) to the top plate assembly (No. 7) using the hitch pins and hairpin cotters (No. 14).

  3. Attach a sleeve (No. 2) to the bottom of each leg (No. 1) using a hitch pin and hairpin cotter (No. 14). The sleeve allows the length of the tripod's legs to be adjusted.

  4. Depending on the type of ground under the tripod, attach the foot and plate assembly (No. 4) to each leg (No. 1) using a hitch pin and locking hairpin cotter (No. 14).

  5. Attach the snatch block (with the cable running through it) to the eyebolt.

  6. With the assembled tripod lying on the ground and with plenty of slack in the cable, have one person pull one leg of the tripod forward while two persons push the other two legs up until the tripod is standing.

  7. Adjust the lengths of the legs until the tripod head is relatively level, keeping the legs evenly spaced.

  8. Using a level, make small adjustments to the legs so the tripod head is level, keeping the legs evenly spaced.

  9. Attach the chain to the hook on each of the foot and plate assemblies. The chain prevents the legs from spreading.

  10. After completing the rigging setup (connecting the cable to the anchors, attaching the Griphoist to the cable, attaching the load to the snatchblock, and attaching a tether line to the load) load the cable slowly and gently. If the tripods shift, repeat steps 7 and 8 until the tripods are loaded and level.

Drawing

MTDC Drawing No. 1035 (PDF - 759 k) shows how to construct the portable tripods.

About the Author

Bob Beckley received a bachelor's degree in political science from the University of Montana in 1982. He began his Forest Service career as a timber technician on the Nez Perce National Forest. Bob was a smokejumper when he joined MTDC in 1990. He works as a project leader, public affairs specialist, and blaster.

Additional Information

Single copies of this document may be ordered from:

USDA Forest Service, MTDC
5785 Hwy. 10 West
Missoula, MT 59808-9361
Phone: 406-329-3978
Fax: 406-329-3719
E-mail: wo_mtdc_pubs@fs.fed.us

Electronic copies of MTDC's documents are available on the Internet at:

http://www.fs.fed.us/t-d (Username: t-d, password: t-d)

For further technical information, contact Bob Beckley at MTDC:

Phone: 406-329-3996
Fax: 406-329-3719
E-mail: rbeckley@fs.fed.us

Forest Service and Bureau of Land Management employees can search a more complete collection of MTDC's documents, videos, and CDs on their internal computer network at: http://fsweb.mtdc.wo.fs.fed.us/search.


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Updated: 04/14/2014
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