Suspension Bridge (French)

This design is taken from a handbook for French Scouts and was originally designed to use 8m spars but we scaled it down as very long spars are not readily available on campsites.

Equipment

• 13 x 15ft (5m) spars
• 9 x 6ft (1.8m) spars
• 4 x 8ft (2.4m) spars
• 36 Lashing lengths
• 2 x 40m ropes 18mm in diameter (approx)
• 2 x 50m ropes 18mm in diameter (approx)
• 4 x 20m ropes to fit the pulleys
• Miscellaneous ropes for attaching blocks to pickets; drawing deck support across ravine; attaching decking
• 2 double blocks and 2 single blocks to fit your ropes ropes for temporary guys + pegs
• 8 pickets
• Mallet
• Sledgehammer or maul

Method

Make two identical rectangular frames. Each one takes 2 x 15ft (5m) spars, 2 x 6ft (1.8m) spars and 2 x 8ft (2.4m) for cross bracing. The 6ft (1.8m) spar between the butt ends of the 15ft (5m) spars should be approx 1ft (0.3m) from the butts to allow for them to be heeled in when the frame is standing upright. The cross bracing should be as near to the top of the frame as possible.

Using the remaining 8 x 15ft (5m) spars, lash them together in two groups of four. The spars should overlap by 3ft (1m). Use a sheer lashing at the ends of each overlap.

Place the two lengths of 4 spars about 3ft (1m) apart then join them using 3 x 6ft (1.8m) spars. Use a square lashing that goes round both the 15ft (5m) spars to form the bridge deck support.

Attach 4 temporary guys to each of the frames.

Lay the frames in position on the ground with the lower cross members underneath and the butts towards the ravine. Ensure that when these are raised vertically that the deck support will span between them.

Attach one end of 2 of the 40m ropes to the top cross bar of the left hand frame using a round turn and two half hitches. Pass the ropes across the ravine and lay them over the right hand frame. Repeat using the other 2 x 40m ropes, tying them to the right hand frame and taking them over the ravine and across the left hand frame.

Put in 4 temporary pickets and make the ends of the ropes off to them.

Drive two more pickets in on each side, between the temporary ones. Attach a single block to each one.

Lay the 2 x 50m ropes across the ravine so that they lay over the frames. Attach a double block to each end of these ropes. Reeve each of the four sets of blocks (ie using the 20m ropes tie one end to the eye of the single block, take the other end of this rope through one of the pulleys on the double block, then go round the pulley on the single block and finally round the last pulley on the double block. Make off the free end onto the picket to prevent it pulling out).

Raise the two frames so they are facing each other. Heel in the butts so that the bottom spar rests on the ground and peg out the guys.

Pass the deck support between the two vertical frames.

Untie one of the 40m ropes from its picket. Pull it down carefully (don’t let it come off the top of the frame). Tie a clove hitch with the cross over underneath using the two loops method, round the 6ft (1.8m) on the deck support nearest to the vertical frame round which the rope is tied.

Note:
The distance of the picket from the frame should be twice the height of the frame.

The position of the temporary picket should be adjusted accordingly. Tie the end to the picket again.

Repeat for the other 40m ropes.

Once all 4 ropes are in place, make sure that they are pulled tight.

Slacken off the two sets of pulleys on one 50m rope and draw down the centre to tie a clove hitch round the centre deck support, with the cross over underneath as before.

Repeat with the other 50m rope.

Carefully adjust all four pulley systems together to achieve even support for the centre of the bridge.

Make off the pulley ropes to their pickets.

Add your bridge deck using some 50 x 5ft (1.5m) spars or other suitable material.

Helpful Hint:
To fix block to the rope, tie a round turn and two half hitches through the eyelet on the block.

Seize the running end to the main length of the rope using twine or sisal using a sheer lashing.

This ensures that the rope will not work loose from the block during tensioning.

Note: Since the design of the project the principles of Health and Safety have changed dramatically.
Caution should be exercised to assess the risks associated with this build and especially regarding possible falls from height, so handrails or belays and harnesses may be required.

To download the complete plan and design document please Click Here