Friends of the Cerberus and the National Trust Australia (Vic) have had a billboard placed in Beach Rd almost opposite the Half Moon Bay car park entrance to raise awareness of what authorities intend doing to our former colonial flagship HMVS Cerberus.
Billboard Side Panel Detail. Click image for hi-res print copy.
Cheaper than concrete Injecting structural polyurethane under the two gun turrets on Cerberus will not only support the turrets but will also allow the four 18 ton guns to be returned to the turrets. An indicative quote puts the cost of this polyurethane approach at under $600,000 whereas the cost of filling Cerberus with 4,000 tonnes has been quoted by Bayside at $720,000.
On the 24th of October 2017 the Bayside Council was advised by its officers that filling Cerberus with concrete would not provide enough structural support to allow the four guns to be returned to the ship.
Environmentally sound The Technical Date Sheet for the structural polyurethane quoted in the indicative quote states "The product has been independently tested and verified to meet NSF/ANSI Standard 61.5 for contact with potable [drinking] water." The Data Sheet further states "Cured material is environmentally safe".
Reversible Experiences with removing polyurethane from vessels overseas indicates that this can be done with high pressure water hoses and hand mattocks. In spite of Bayside's claim that concrete could be removed from Cerberus the experience of removing it from the Bayou St John in the US state of Louisiana indicates that doing so with Cerberus would cost in excess of $100 million. This assumes that Cerberus was on dry land, which of course it isn't. Effectively, removing concrete from Cerberus is not possible and the process is therefore not reversible.
Article 15.2 of the Burra Charter (the gold standard for conservation in Australia) states "Changes which reduce cultural significance should be reversible and be reversed when circumstances permit. Bayside's submission misquoted from the Burra Charter in order to suggest that the Burra Charter accepted that non reversible changes were permitted in certain circumstances. The blue text below in the notes from article 15 of the Burra Charter was quoted whereas the red text was omitted from Baysise's permit application.
"Reversible changes should be considered temporary. Non-reversible change should only be used as a last resort and should not prevent future conservation action."
As concrete is not reversible and its presence would prevent any future conservation its use is in clear contravention of the Burra Charter and should therefore not be used.
Will prevent collapse The Geotechnical study undertaken by GHD in 2003 indicated that the main factor likely to cause Cerberus to collapse was the looming collapse of the two gun turrets. A continuous layer of polyurethane under each turret would support around 843 tonnes. Even assuming that it is not possible to provide a continuous layer of polyurethane under each turret, as the weight of a gun turret is only about 173 tonnes, there is a huge safety margin.
On the contrary, as stated above, Bayside Council has been advised that filling Cerberus with concrete would not provide enough structural support to allow the four guns to be returned to the ship. Given that Bayside has not done any engineering studies on the effect of concrete on Cerberus it is unlikely that they have concluded that any concrete that does provide support for the turrets can support 173 tonnes but not 209 tonnes that the turrets weigh with their guns. If this is the case then one must conclude that the concrete infill will not support the turrets with or without their guns.
As polyurethane would be injected under pressure under the gun turrets until it pushed upwards against their underside, it would support them. The much denser concrete that did make its way by gravity under the turrets would most likely cease flowing at any obstructions and would in any case not be forced upwards until it hit the underside of the turrets. This is most likely the basis of Bayside's admission for the lack of structural support provided by concrete for the turrets.
Won't damage ship
Polyurethane in-fill provides a viable conservation remedy, wouldn’t damage the ship and would be easily removable in the future as other more permanent conservation efforts are undertaken. Concrete by comparison would likely destroy the Cerberus.
David Johnson is a metals corrosion expert and a registered Objects Conservator with the American Institute for Conservation of Historic and Artistic Works who worked on the conservation of the Bayou St John, an historic Civil War era submarine in New Orleans, USA. The submarine had been filled with concrete in 1934 and modern conservators realised that it was destroying the vessel and needed to be removed.
“Not surprisingly, we found that the concrete caused extensive corrosion.” Johnson said. “There’s a good chance that pouring concrete into a ship like the Cerberus would destroy it over time.”
Johnson has advised that pouring the concrete all at once would place an unsupportable outward load on the hull unless there was extensive and costly bracing. The alternative technique of pouring concrete in stages would increase the likelihood that increased pressure on the hull plate at each stage would allow wet concrete to leach between the hull and the hardened concrete layer below, which would cause increased corrosion.
“Corroded metal occupies seven times the volume of uncorroded metal. A likely outcome would be increased pressure against the hull as the corrosion pushes against the concrete. We’re talking thousands of pounds of pressure developing over time. That would very likely break the hull plates.”
So, the technique isn’t simply unproven, in fact it has been discredited and proven to be disastrous.
Proven method No damage from polyurethane has been reported from the numerous instances where polyurethane has been used to salvage vessels or for ongoing use in vessels. Examples such as the Cutter Suction Barges used in NSW, the USS Frank Knox, the bulk carrier Sidney E. Smith and the barge Lumberjack denonstrated the viability of polyurethane injected into vessels either on the surface or on the seafloor and the relative ease with which it can be removed.
Concrete: a discredited 1930s method.
In 1934, conservators of the historic Civil War submarine, the Bayou St John, filled it with concrete in the misguided belief that it would support the hull. The complicated process of later removing it led conservation experts in the State of Louisiana to describe the use of concrete as an extremely costly mistake.
Greg Lambousy was curator on the project to restore the submarine.
“The concrete was actually destroying the submarine, we knew we had to remove it if we were to preserve it,” Lambousy said. “Doing that took us 6 years and cost over $60,000 ($83,000 AUD) just to remove near a tonne of concrete. Given our experience with the submarine, we wouldn’t encourage others to fill ships with concrete if conservation is the goal.”
This experience in Louisiana shows that filling historic ships with concrete is a very old-fashioned and discredited heritage approach.
After seventeen years of searching for a solution to prevent the collapse of HMVS Cerberus at Black Rock, a meeting was convened in April 2017 to which two of the key stakeholders, Friends of the Cerberus and the National Trust, were not invited. Both uninvited groups had co-nominated Cerberus for inclusion on the National Heritage List while Friends had obtained the $500,000 NHII grant that the National Trust was the custodian of.
From then on three levels of government conspired to implement an unsound heritage solution without consulting the two community groups.
According to the then Mayor of Bayside, the Federal Heritage Department and Heritage Victoria representatives indicated that filling Cerberus with concrete was the way forward and proposed using the NHII grant for this purpose. Friends was informed of the decision of this secret April meeting in late May while the National Trust only found out on the day of the Bayside Council meeting that decided to commence the concrete planning process.
A superior solution of injecting structural polyurethane under the gun turrets was conveyed to Bayside but was not forwarded to the archaeologist writing the application for a permit from Heritage Victoria to fill Cerberus with concrete. Bayside's permit application contained inaccurate claims about the polyurethane solution, misquoted from the Burra Charter (the gold standard of heritage conservation) and omitted relevant information about the shortcomings of the concrete approach.
To their credit Heritage Victoria did allow objections to the permit application but then appeared to take no notice of them. Their reasons for rejecting polyurethane suggest that the submissions were not even read.
Polyurethane is cheaper than concrete, adds no weight to the ship, will support the turrets and allow the guns to be returned to the ship, is environmentally safe, has been used in marine environments since the 1960s and is reversible.
Concrete on the other hand will more than double the weight of the ship causing it to settle, will not support the turrets or allow the guns to be returned and is not reversible. To top it off, the concrete fill approach has been used in the past and deemed a bad conservation practise. A vessel of the same age as Cerberus was filled with concrete in 1934 only to have the concrete removed at great cost in 2000. Because of the location and quantity, removal will not be an option for Cerberus. Future generations will laugh at us and condemn us for implementing such an unsound supposed solution.