The actual size of the spars used in this project will depend on the size of the obstacle being bridged. If you assume a gully about one metre deep with sloping sides, so that the bottom is 1.5m across and the banks are 4m apart you will need. . .

Equipment

- 2 x spars 3.6m long
- 12 x spars 2m long
- 12 x light spars 1.24m long
- 30 lashing lengths

Method

Make 2 rectangular frames from the 2m spars. The top sections must be able to interlock to form the fulcrum for the see saw. The actual position of the two top spars will have to be estimated on site as the aim is to provide a pivot point about 0.25m above the top of the banks when the trestles are standing in the gully. (a)

The walkway takes the form of a ladder. Place the 3.6m spars parallel to each other with their butts at the same end. They should be spaced so that they will sit inside the top of the trestles. Space out the 12 light spars evenly along the length. Lash the end ones under the ladder and the rest on the top.

To complete the bridge, place the trestles either side of the base of the gully with their tops interlocked in the centre. Lift the ladder on to the top of the trestles and position it so that the ends reach the banks.

Health and safety probably demands a hand rail . . .