John Thurman was Camp Chief at Gilwell Park during the 1950’s. Whilst on a visit to Tasmania he was very taken with the bridge across the harbour at Hobart. This was a great crescent shaped floating pontoon with a lifting section adjacent to the quay to allow ships to pass through. The Hobart bridge inspired the design for “Tassie” which can be tailored to suit the width of any river, and, for narrow rivers, you could just build the lifting section.
- 4 x 5m (16 ft) spars
- 2 x 2.4m (8ft) spars
- 3 x 4m (12ft) spars
- 11 x 2m (6ft) light spars
- 12 lashing lengths
- 1 x 15m (50ft) rope to fit blocks and 1 x 12m (40ft) rope to fit blocks
- 1 single wheel pulley
- 1 double wheel pulley
The pontoon consists of two parallel lines of drums supporting a ladder constructed out of spars and light spars. It can be whatever length is necessary to reach from the bank opposite the lifting section to the lifting section.
- 2 long spars for the sides of the ladder (or several smaller ones)
- light spars for the ladder rungs 1.2m (4ft) long
- lashing lengths
- 2 stakes or pickets
Prepare the two sides of the pontoon either by selecting long spars of suitable length or by lashing spars together with sheer lashings to provide the required length.
Lash 1.2m light spars between the two side spars using square lashings at approx 0.3m (12″) centres to produce a ladder. Ensure all the light spars are on the top of the ladder.
Turn the ladder over and lash further 1.2m light spars across the ladder in alternate gaps between the rungs.
Lash each drum separately to the sides of the ladder. The drums should lie along the length of the side spars of the ladder, starting approx 1m (3ft) from one end and be spaced evenly.. There are a number of ways for tying the drums onto the spars and you should use whichever works for you – we suggest a clove hitch round each end of the drum then the ends of the ropes tied to the spars as tightly as possible using a round turn and two half hitches.
Turn the ladder over so that the drums are underneath.
The pontoon is then placed in position with one end firmly on the bank. Stakes are driven in on either side of it and it is firmly lashed to them.
A weight must be tied to the river end of the pontoon to prevent it floating away – several engineering bricks (the ones with holes in) on a length of rope should be sufficient – remember to allow enough rope for the rise and fall if your river is tidal.
Using 4 x 5m (16ft) spars and 2 x 2.4m (8ft) spars, prepare two identical A frames with the cross bars as high as possible (you will need to walk underneath them).
Prepare a ladder using 2 x 4m (12ft) spars and 12 x 1.5m light spars. The last rung of this ladder at the pontoon end should be some 0.3m from the end of the side spars. The bridge rests over the end of the pontoon when lowered.
Lash a 4m (12ft) spar between the top of the A frames.
Hang a double pulley from the spar which joins the A frames at the bank end and the single pulley from this spar at the river end, using a round turn and two half hitches.
Thread the 15m (50ft) rope through both pulleys and tie it off to a loop attached to the river end of the ladder. Thread the other rope through the double pulley and tie off to a loop at the bank end of the ladder. These loops should be fairly long as you will need to climb through them when using the bridge, but short enough to allow the bridge to be raised.
Manoeuvre the A frames into position and embed the feet of one into the bank. The other A frame should stand over the end of the pontoon. Guy as necessary.
By standing on the bank the bridge can be raised and lowered by pulling the ropes through the pulleys – remember to tie them off securely once the bridge is in the required position.
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