The Timeball Station in Lyttelton is to be dismantled.
The New Zealand Historic Places Trust (NZHPT) said it has taken the step "with enormous regret" but said public safety is paramount.
The Timeball Station is a Category I historic place and is internationally significant because of its maritime history.
NZHPT said its decision is based on specialist engineering information and guidance, but added the work will pose problems because of the steep site.
"People around the world have seen images of the extensive damage caused by the quake on 22 February, which has compounded damage sustained in the earthquake on 4 September last year," chief executive Bruce Chapman said.
"The Timeball Station is too damaged and too dangerous for us to consider anything other than dismantling.
"This is an extremely difficult site. It was chosen as a building site over 135 years ago for the Timeball Station because of its elevated position, allowing ships to see it clearly from the harbour. That's now working against us," Chapman said.
He said workers are constrained by issues of access and also the risk of injury to anyone involved.
"We are not prepared to put anyone's life at risk."
But Chapman said if they can they will find a way to dismantle the Timeball Station that retains as much of the building's materials as possible.
"This site remains significant and we would hope that in future we can do justice to this important building."
NZHPT is hopeful the Timeball mechanism can be recovered.
About the Timeball Station
From 1876 to 1934 a ball dropped from the Timeball Station's mast on its stone tower, signalling the time to ships in Lyttelton Harbour. Visual time signals were important features of many of the world's ports, being necessary to correct ships' chronometers and ensure accurate navigation.
The timeball apparatus came from the well-known German firm Siemens Bros, and the astronomical clock from Edward Dent & Co. of London, who had made the Big Ben clock.
Use of the timeball was discontinued in 1934 when it was replaced by radio signals, though flag signals continued until 1941. The flags, which predated the Timeball Station, were used on the flagstaff nearby to signal to ships and to communicate shipping advice to the town.
After the dropping of the timeball and flag signalling ceased due to the increasing reliance on radio communications, the Lyttelton Timeball Station was occupied by the New Zealand Army in 1942-43. It was then inhabited by various staff members (and their families) of the Lyttelton Harbour Board until 1969 when the Harbour Board began to question its continued ownership of the station. The Lyttelton Maritime Association leased the Timeball Station from the Harbour Board, and began to restore it.
By 1973, it became obvious that the task of maintaining and restoring the property was too great for a volunteer organisation and it was agreed that it would be gifted to the NZHPT. The Ministry of Works and Development took over the restoration of the station, the timeball and its mechanism in 1975, working with the NZHPT. The restoration project was completed by the end of 1978 when the Timeball Station was officially reopened.
A fine example of Victorian technology, until the earthquake the
Timeball Station was one of only five in the world known to be
still in working order - making it a rare piece of maritime
Quake appeals have been launched. Find out more here.
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