The immediate success of the first slipway led the
Wellington Provincial Council to investigate building a bigger slip that could handle larger ships. In December 1863, the New Zealand Government passed empowering legislation authorising the Superintendent of Wellington to compulsorily acquire an area of land up to at Evans Bay for the construction of a larger Patent Slip. The Wellington Provincial Council was keen to have a slip capable of taking large vessels to increase the attractiveness of
Wellington Harbour for the shipping trade. However, the Provincial Council was unable to fund the construction, and decided to grant a
concession for a slipway to be built and operated. The concession was granted to Kennard Bros., of London. Kennards manufactured and delivered hundreds of tons of machinery to Wellington in 1866. In 1871 Wellington businessmen formed the Wellington Patent Slip Company and bought the equipment from Kennards. Construction began in 1871 and was completed in May 1873. The Evans Bay Patent Slip, the first in New Zealand, was a major engineering achievement. A 200-ton, cradle moved on wheels along parallel rails. Two chains were used for hauling vessels out of the water and lowering them back down. The chains ran over a cogwheel winch powered by two steam engines. The main 'hauling up' chain was long and weighed 62 tons. Each link was long and made of iron thick. One end of the chain was attached to the cradle and the other dropped into a well beneath the winding gear. The smaller 'lowering out' chain was a loop with links thick. This was used for lowering ships down the slip and for bringing up the empty cradle. This was the first large-scale underwater construction in New Zealand. A jetty was also erected to improve communication with ships. Along with housing for the winches and boilers required to operate the slipways, there were some houses, a store, an inspector's office, a carpenter's shop, a
messroom, and a blacksmith's shop. A small vessel could be raised up the slip in about 20 minutes, and a larger ship could be raised at a rate of . By the late 1890s there were calls for a
dry dock in Wellington, amid claims that the Patent Slip could not cope with the increased size and number of ships visiting Wellington. Early in 1908, the
Union Steam Ship Company (Union) acquired 90% of the shares in the Wellington Patent Slip Company. In July 1908, after months of meetings and negotiations with the Patent Slip Company and Union,
Wellington Harbour Board acquired the property where the slip was located. Under the agreement, the Patent Slip Company would continue to manage the slip for the next 25 years and build a second slip if required. This was constructed in 1922. In 1961, Union chose not to renew its lease, so the Harbour Board took over management of both slips until 1969. At that time slipway No. 1 was taken out of service and slipway No. 2 was upgraded. The slipway closed on 31 July 1980. The site was demolished and various equipment scrapped, sold or given to museums, and land was filled in for a new housing subdivision. The site was listed as a Category 2 historic place in 1982. Wellington City Council had the site rezoned as a heritage area in 2003, and the area is now known as Cog Park. ==Incidents at the slip==