Drawbridge v2
Equipment
- 4 x 5m (15ft) spars
- 6 x 4m (12ft) spars
- 2 x 2m (6ft) spars
- 2 x 1.5m (5ft) spars
- 7 x 1.2m (4ft) spars
- 6 x 1m (3ft) spars
- 1 log approx 2m (6ft) long
- Lashing lengths
- Pulleys – 1 single and 2 double (at least one with a hook)
- Light line
- 1 x 15m rope and 1 x 40m rope to fit pulleys
- Spars to form a temporary ladder 3 x 2m (6ft)
- Pegs, mallet, 1 picket and a maul or sledgehammer
Method
Prepare an A frame using 2 x 4m (12ft) spars and 1 x 2m (6ft) spar
2 x 5m (15ft) spars should be lashed approx 1m (3ft) below the sheer lashing at the apex of the A frame. These lashings should be slightly loose as, when the A frame is standing upright, the spars need to slope down to the ground.
1 of the 1m (3ft) spars is then lashed to the 5m (15ft) spars just above the lashing joining them to the A frame and a second 1m (3ft) spar lashed to the A frame as close to the previous 1m spar as possible. Take care to allow enough space for the 5m (15ft) spars to move.
Tie guy ropes to the top of the A frame.
Stand the A frame upright and support it by resting the 5m (15ft) spars on the ground. Guy in place.
Lash 2 x 4m (12ft) spars on top of the lower bar of the A frame, in the corners. These spars should stick out beyond the A frame by about 1m (ft). Lash the other ends to the 2 x 5m (15ft) spars.
Join these 2 x 4m (12ft) spars with 1 x 2m (6ft) spar. This spar should be inside the triangle formed at the side by the A frame, 1 x 4m (12ft) spar and the sloping 5m (15ft) spar.
At the corner of the side of the frame, stand a 1.2m (4ft) spar on the ground. It should be close enough to the corner that it can be lashed to both the bottom spar and the sloping one. This will provide some bracing for the frame and also be another point of contact with the ground.
Repeat on the other side of the frame.
Prepare a tapering ladder using 2 x 4m (12ft) spars and the remaining 1.5m (5ft) and 1.2m (4ft) spars. At the wider end, the first rung should be approx. 1m (3ft) from the ends of the 4m (12ft) spars.
With the rungs on the top of the ladder, lash the log under the wider end of the ladder between the first rung and the ends of the 4m spars.
Rest the log on the ends of the 4m (12ft) spars where they stick out beyond the A frame, close to the A frame but allowing sufficient space for the log to pivot as the gate is opened. Lash a 1.5m (5ft) spar to the end of the 4m (12ft) spar and the A frame to form a triangle to contain the end of the log. Repeat of the other side.
Lash 3 x 2m (6ft) spars onto the A frame to form a temporary ladder and, using this, climb up to attach one of the double pulleys to the centre of both of the 1m (3ft) spars lashed to the A frame.
Take the 15m rope and pass both ends through the suspended double pulley so that the resulting bight is facing away from the river/ravine. Tie of the ends of the rope to the far ends of the ladder.
Using a catspaw, attach the remaining double pulley (the one with the hook) to the bight in the 15m rope.
Mouse the hook.
Drive the picket in 8m (25ft) behind the structure and attach the single pulley to it.
Use the 40m rope to reeve between the single and double pulleys in the usual way.
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
