The two 10.5m x 13.5m steel gates have been constructed to withstand a one-in-200-year storm event, and will be capable of reducing a 4m wave outside the harbour to just 400mm inside the marina.
They were installed by specialist marine civil engineering contractor Land & Water, with design services provided by Opus International. Ainscough Crane Hire provided the lifting muscle.
The £4m King Point Marina project is being developed by waterfront regeneration specialist Sutton Harbour Holdings. Exeter-based construction company Devon Contractors is building the shoreside facilities and the piling and installation of pontoons has been carried out by Walcon Marine.
Completion is scheduled for September 2013.
King Point Marina will provide sheltered berths for vessels from 5m to 25m in length. The two-storey shoreside building will provide amenities for berth holders.
The wider Millbay area is being developed by English Cities Fund (ECf), which is a joint venture between Muse Developments, Legal & General Property and the Homes & Communities Agency.
"The installation of the wave gates at King Point Marina is a major milestone for the project, and a truly impressive feat of engineering - the last time anything like this was carried out in Plymouth was the installation of the lock gates at Sutton Harbour back in 1993,” said Sutton Harbour Holdings chief executive Jason Schofield.