Work to transform Weymouth & Portland's sailing facilities for 2012 is "racing towards the finishing line", the Olympic Delivery Authority (ODA) said.
The new Weymouth & Portland National Sailing Academy will host the Olympics and Paralympics sailing events.
In March, contractors, Dean & Dyball, began constructing a new 250m (820ft) slipway, along with race-boat parking, lifting and mooring facilities.
The world class venue is expected to be completed in November.
The authority said the work was "well over the halfway stage".
About 70,000 tonnes of Portland stone will be used to form the new slipway.
A 200m (656ft) breakwater to protect the new facilities has been completed and work is also well underway on a new pier, offering two yacht-lifting cranes and a new pontoon to provide 70 berths for race-boats.
The news follows the British sailing team's success at the Beijing Olympics with six medals won, four of them gold.
ODA chief executive, David Higgins, said: "Weymouth & Portland was the first venue for 2012 to start construction work so reaching the final stages of the project is another important milestone.
"The huge progress we're making at Weymouth & Portland means we're on course to finish work ahead of schedule."
Sebastian Coe, chairman of the London 2012 Organising Committee, said he was "delighted" that the work at Weymouth & Portland would allow sailors "to train well ahead of 2012".
Weymouth and Portland Borough Council gave planning permission for the £21m Portland Marina at Osprey Quay in June 2007.
The plans include a 560-berth marina, which will be sheltered by the stone breakwater.
There will also be an on-shore reception centre with washrooms, showers and laundry facilities and a restaurant bar overlooking the harbour.
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