The Burma bridge is basically a three-rope suspension bridge -- one rope for the feet and one for each hand. It might look like something designed as a special effect for an Indiana Jones movie, but it is a popular elevated element in military training courses and commercial adventure experiences. A serviceable demonstration Burma bridge of prepared materials that will support up to 700 pounds can be assembled in under an hour, using basic rope-handling skills such as the clove hitch and square lashing.
Items you will need
- 4 pine or oak 2-by-4 boards, 8 to 10 feet long
- 2 2-by-4 boards, 3 feet long
- 2 2-by-4 boards, 4 1/2 feet long
- 2 2-by-4 boards, 6 feet long
- 1 natural fiber foot rope, 1 inch in diameter and 100 feet long
- 2 natural fiber hand ropes, ½ inch in diameter and 150 feet long
- 14 lengths of braided polyester rope, ¼ inch in diameter and 12 feet long, for lashing
- 15 lengths of braided polyester, ¼ inch in diameter and 10 feet long, for stringers
- 1 3X block and tackle expandable to 10 feet
- 2 burlap bags, 22 by 36 inches
- 2 wood stakes, 3 inches in diameter and 5 feet long
- 1 short heavy rope to attach block and tackle to anchor point
Select SiteStep 1
Pick a place to assemble the bridge that offers two natural anchor points -- stout trees, large rocks and/or utility poles -- about 60 feet apart.
Use a holdfast if a second anchor point is not available. A holdfast is a wooden or metal stake about 3 inches in diameter and 5 feet long that is driven at least half its length into the ground and angled at 15 degrees away from the angle of pull.
Unload and lay out all materials in the sequence they will be used.
Build TrestlesStep 1
Lay two long 2-by-4 boards on the ground and cross them at about one-third of their length to form a lopsided X.
Lay one of the 6-foot 2-by-4s across the bottom of the X so that the ends extend beyond the long boards at least 6 inches on each side. Lay one of the 4 1/2-foot boards across the middle of the larger part of the X with the ends extending the same distance. Lay one of the 3-foot boards across the lower part of the X between the long boards above the middle board but below the crossing point of the X with its ends extending the same distance.
Lash each of the seven points where the boards cross each other with a 12-foot length of braided polyester rope, using square lashing.
Assemble the second trestle with the remaining 2-by-4s and lashing ropes.
Lay Out Long RopesStep 1
Secure the ends of the foot rope and the two hand ropes to the first anchor point at the chosen height above ground level, using a round turn and two half-hitches.
Stretch all three ropes out along the ground to the second anchor point.
Attach the block-and-tackle to the second anchor point with the short heavy rope and lay it out toward the first anchor point.
Form a loop in the footrope at the point where the footrope and the block-and-tackle meet, with a bowline knot or a figure eight and a half. Avoid using an overhand knot, as it will be difficult to loosen later.
Connect the footrope to the block-and-tackle.
Attach TrestlesStep 1
Lay a trestle under the long ropes with its bottom toward the first anchor point and its top about 10 feet from it. Fasten the hand ropes to the tops of the long 2-by-4s, using a clove hitch. Raise the top of the trestle until it forms a 45-degree angle with the ground with the bottom cross-piece at 90 degrees to the first anchor point. The trestle should be leaning away from the first anchor point. Check the hand rails to ensure that they bear equal tension. If they do not, adjust the clove hitches until the hand ropes match.
Place the second trestle under the ropes in a similar position, with its base toward the first anchor point and its top about 10 feet from the second anchor point. Check that the bottom is perpendicular to both anchor points. Tie the hand ropes to the tops of its long 2-by-4s with clove hitches. Raise this trestle to 45 degrees, leaning toward the first anchor point. Make any necessary adjustments in the hand ropes between the trestles to create matching parallel curves by slipping the clove hitches.
Pass the end of each hand rope around the second anchor point above the block-and-tackle and secure it with a trucker's hitch. Leave about 2 inches of space between the hand ropes as they pass around the second anchor point, so that they do not interfere with each other, but still remain on the same level.
Reposition the second trestle so that it is leaning away from the second anchor point and the hand ropes are about 5 feet off the ground but can still be reached by someone standing on the ground.
Fold a burlap sack in half and lay it lengthwise through the upper side of the crossing point of each trestle's long 2-by-4s to protect the lashing there from abrasion by the foot rope passing over it.
Add StringersStep 1
Tighten the block-and-tackle on the foot rope until it stretches parallel to the hand ropes in a matching curve.
Begin a spot in the lowest point of the curve of the ropes and select a 10-foot stringer rope. Tie one end to a hand rope with a round turn and two half-hitches. Pass the stringer vertically to the foot rope and tie a clove hitch around it at the center of the stringer rope. Carry the free end of the stringer rope back to other hand rope and secure it there with another round turn and two half-hitches. The stringer should now form a V with the knots at the hand ropes as the upper points and the foot rope as the lower point.
Add another stringer at the approximate midpoint between the center stringer and one trestle.
Add another stringer at the approximate midpoint between the center stringer and the opposite trestle.
Continue adding stringers by halving the distance between one stringer and another and between stringer and trestle at each end. This should provide a stringer every two feet or so on a bridge approximately 30 feet long.
Raise BridgeStep 1
Reposition both trestles to fully upright by swinging the bases toward the center of the bridge.
Tighten the hand ropes evenly and individually with the trucker's hitches until they have no curve and will support the weight of a person hanging by the hands.
Swing the base of each trestle toward the nearest anchor point about 5 degrees to ease the climb up to the bridge.
Tighten the foot rope with the block-and-tackle until it is rigid and will support the weight of a person.
Tips & Warnings
- The crew must be familiar with the parts of the bridge and know how to tie all the knots specified to be able to assemble the bridge in the specified time -- practice and teamwork are needed.
- This is a good project for a scout troop, with plenty of adult supervision.
- In a demonstration, have a team member walk on either side of each person crossing the bridge.
- Check all knots frequently during a demonstration.
- Examine all materials for wear or weakness at the end of each demonstration and replace as necessary.
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