Hobart's Floating Bridge
The floating bridge alongside the Tasman Bridge prior to its completion
The original bridge which spanned the Derwent River where the Tasman Bridge now stands between 1943 and 1964 is unique in that it was one of if not the only permanent floating road bridge ever built in Australia. The first plans for bridging the Derwent River close to Hobart date back to 1832 but a hurdle to overcome would always be the width of the river here. A solution birthed back then and used in the original Hobart Bridge many years later came from Captain Jacobs who proposed a floating timber structure consisting of short spans linked by barges anchored across the river.
The Bailey bridge was built and opened in 1943, however it varied from Jacobs' design by having a lift span on the eastern shore to allow vessels to pass upstream, and a floating arch section of two reinforced concrete sections anchored to the abutment and lift span. The lift span weighed 350 tons and could be raised 46 metres in two minutes. From 1943 until 1948 a toll of 2 shillings (20 cents) applied to cars until 1946 when it was reduced by 1 shilling. Utilities were charged 1 shilling 6 pence (15 cents) and passengers over the age of 14 were charged 3 pence (3 cents).
The Gothic, which brought the Queen and Duke of Edinburgh to Hobart in 1954, passes under the lifting arch of the bridge. Photo: Trams Downunder Archive
Considerable grow of the suburbs of Hobart on the eastern side of the Derwent River resulted in the bridge having reached a severe level of congestion by 1955, particularly when the lift span was raised for shipping. Over the years, the bridge had been battered by numerous storms and after one particularly bad storm, a careful examination of the floating part of the arch bridge revealed it had sustained sufficient damage to limit the life of the bridge were it to stay in its present position.
A decision was then made to replace it with a larger bridge. Construction of its replacement, the Tasman Bridge alongside it, commenced in April 1960. By February 1964 only a small gap had to be finished. The Tasman Bridge was finally opened to traffic on 17th August 1964. The floating arch of the old Hobart Bridge was removed on 18th and 19th August, 1964. Both sections were towed and stored at Geilston Bay pending a decision on their future.
In early November 1970, one of the moored half-arches of the Hobart Bridge sank in Geilston Bay. It was successfully raised on 23rd February 1971. Each half-arch was cut into three lengths of 161 meters long and weighing 4000 tonnes. The three sections from the raised half-arch were disposed of, two sections on 24th and 25th May 1971 at Betsey Island, and the third section on 16th July 1971 off Droughty Point in Ralphs Bay. Two of the three remaining sections from the second half-arch were disposed of by sinking them off Betsey Island on 16th and 17th November 1971. The final section was positioned and sunk at Alonnah on 27th June 1972 and remains as a breakwater.
Today the only reminders of the bridge are the remants of the bridge's east side on-ramp, the eastern foot of the lifting section which is still in place, and the preserved locking pin.
Photo: Trams Downunder Archive
Length of roadway between shore abutments, 1.16 km
Approximate cost, 500,000 pounds
Construction Commenced, 1938
Lift span opening, 55 m between pier protections.
Vertical clearance of lift span, 44.4 m at Mean Water Level.
Weight of towers and lift span, approximately 900 tonnes.
Weight of lift span only, 350 tonnes.
Weight of steel in lift span towers, 280 tonnes.
Weight of steel in lift span, 192 tonnes.
Roadway width on lift span, 6.7 m
Time taken to lift opening span, 2 minutes.
Arch floated into position, 22nd October 1943.
Damaged by storm, 4th December 1943.
Opened to toll traffic, 22nd December 1943.
Tolls abolished, Midnight 31st December 1948.
Bridge closed to traffic, 17th August 1964.
Arch removed and stored, 18th and 19th August 1964.
Lift Span Machinery: Two 50 H.P., 600 R.P.M electric motors in operating house over centre of span. There were also auxiliary motors for opening in case of power failure.
Floating Arch: Consisted of two reinforced concrete sections anchored to the eastern shore abutmentand lift span. Joined at the centre by one 33 cm vertical pin, each half of the arch was cast in ten x 40 m lengths, with one x 38 m and one x 42.2 m The average weight of each length was approximately 1,000 tonnes. The weight of each length was approximately 25,000 tonnes. The length of roadway on arch is 961 m. Overall width of arch at deck level is 12.3 m including roadway, footway, kerbs and ledges. Total concrete used in arch, 8,410 cubic metres. Total steel used in arch, 3,100 tonnes.