Portcullis drawbridge - Pioneering projects for the Scouts



This ingenious device is operated by a Scout standing on top of the back section of the gateway and, as the drawbridge is raised, so the portcullis comes down. The drawbridge can be any length provided it does not exceed the height of the uprights.



Equipment


- 4 x 5m (16ft) spars
- 1 x double sheave block
- 30 x 7m lashings
- 18 x 2m (6ft) staves
- 2 x 3m (10ft) spars
- 1 x single sheave block
- 54 x 3m light ropes
- 2 x .6m (2ft) spars
- 8 x 2.5m (8ft) spars
- 2 pickets
- 1 x 30m rope for pulley
- 1 cable drum
- 6 x 1.8m (6ft) spars

Method

Construct 2 rectangular frames using 1 x 1.8m spar and 3 x 2.5m spars (a).

Stand the frames up approx 1.5m apart and join the top corners using 1.8m spars. Attach guys to the top corners of the structure for stability.

Place a 1.8m spar through the cable drum and lash it between the two side frames, approx in the middle of the top spars.

Lay 2 x 5m spars in line with this structure so that the butts fit inside it - when these spars are raised to the vertical they will be lashed to the bottom spars where they extend beyond the main frame.

Lash 1 x 0.6m spar to the top of each of the 5m spars so that the short spar stands vertically and join them by lashing a 1.8m spar between the centres of the short spars.

Construct the portcullis panel using 6 x 1.8m staves. The width of the panel must match the distance between the 5m spars. The cross bracing should be on the underside of the panel.

Lay the portcullis on the 2 x 5m spars and lay the second pair of 5m spars on top of it. Lash the top end of the 5m spars to the short, vertical spars.

Attach guy ropes to each end of the 0.6m spars and raise the 5m spars so that they stand vertically. The butts should fit between the extended bottom spars of the frame, which has already been built and be lashed to them. Peg out the guys.

Next, the side bracing is added to the structure using the 2 x 3m spars. Take care not to allow them to encroach on the space between the vertical 5m spars as this could impede the movement of the portcullis. The other end is lashed to a picket. The vertical side braces are 2.5m long and are placed approx. half way along the structure.

The drawbridge is constructed next. Place a 1.8m spar on the ground between the pairs of 5m spars and then lash 2 further 1.8m spars to it to act as main members. Staves are then lashed on top of these to form the walkway.

The pulleys and cable drum are rigged in accordance with the diagram.

Either a fixed or rope ladder is needed for access and a handrail 1.1m high should be fixed around the platform.

Complete the platform either side of the cable drum using staves.