Posted by Peter McCurdy on 25 November 2014 | Comments
The Auckland steam ferry Toroa is a large vessel, a ship, of composite construction in the old sense of composite construction – timber planking over steel framing and bulkheads. Much of the original steelwork was badly corroded and has had to be renewed virtually throughout the hull.
And to preserve integrity of structure and shape, renewal of the steelwork must be done from the inside out, before tackling restoration of the hull and deck planking. And so, an extensive body of restoration work has been invisible to the passing motorist.
Renewed steelwork in Toroa’s hull aft of the engine room. Steel bulb-angle frames (ribs) have been bent to shape and bevel while heated to above red heat. Bulkheads have been hot-riveted with 16 & 20 mm diameter mild steel rivets. The steel deck beams in this area have yet to be tackled.
The new steel frames are of bulb angle 120 mm x 75 mm, extruded by Dent Steel of Bradford, Yorkshire to match the original 5” x 3” rolled bulb angle. Bulb-angle frame was commonly used in 19th-century composite vessels – the planking is fastened by bolts through the flange and the bulb increases the section modulus and the stability of the web in bending over those of a plain angle section.
Bending the frames meant reviving and adapting 19th-century techniques. After cold-bending proved unsuccessful, bending the bulb-angle to a pattern on a traditional cast-iron dog-slab was employed, heating the steel to above red heat with a large oxy-acetylene torch gradually swept along the frame, and pulling the frame progressively into the pattern. In successive sweeps the flange was bent outboard to match the bevel required by the planking at the particular station of the hull.
Steelwright Andrew Macbeth & Jackson Brown of ADM Contractors Ltd adjust the bevel in the flange of a bulb-angle frame already bent to pattern.
New frames in the port after-quarter of the hull. Here there is reverse curvature and up to 20° of bevel in the flanges.
Toroa’s large triple-expansion steam engine is housed to the north of the ferry and has been repaired, de-rusted, painted and reassembled. Apart from some work on journals and valves and auxiliaries it is in a state to be lifted back into the hull when that is ready.
The two wheelhouses have been rebuilt using original materials and methods of construction, and one has had its equipment and fittings restored and re-fitted.
The restoration of the Toroa is guided by a comprehensive conservation plan based on well recognised heritage conservation principles and protocols. The purpose of the project is to restore the steam ferry to an authentic and seaworthy state to operate again on the Waitemata. To this end, materials, methods and arrangement are being restored as closely as possible to the original state of the vessel, modified only where necessary to comply with the current maritime regulations, and to meet the requirements of longevity and the need to generate income to fund ongoing maintenance and preservation.
Many organisations and individuals contribute, and have contributed, to this maritime and social heritage project. Substantial grants have been provided by the Lottery Grants Board, the ASB Community Trust and TTCF: Waitakere Licensing Trust, and the Society is supported financially and in materials and services by many others. See Help Us for a list of contributors and for how to join in supporting the restoration of the historic steam ferry Toroa.
Photographs: P.J. McCurdy