Using sonar technology and old records from the NSW Department of Public Works and Royal Australian Navy, self-confessed history “nut” Scott Willan found the wreck about 6.5kms directly east of the Macquarie Lighthouse, near Watsons Bay.
The wreck, which is about 28m long sits upright in 73m of water.
Photos show the rudder and bow of the iron-hulled ship which are clearly distinguishable, despite being covered in seaweed and shellfish.
Mr Willan, who dived the wreck last week, said he is 95 percent sure he can identify the vessel.
“Based on reinterpreted data I have from Public Works and more recent data from a survey by the Navy in the area, I think it’s the SS Yamba, a tug boat that was used in Sydney Harbour,” he said.
Records show the Yamba was a 104-ton iron-hulled, steam-powered tug built by Altas Engineering in 1920 for J. Fenwick and Co., an old Balmain-based tugboat company.
Mr Willan said she was stripped down and then scuttled in 1942.
On its website the NSW Office of Environment and Heritage described the Fenwick Tug Boat Company as the “earliest and pre-eminent tugboat operator on Sydney Harbour.”
“You’ve got to remember this was a time when ships were moving away from steam to diesel powered engines,” Mr Willan said.
“To strip out the old steam boiler to put in a diesel motor would have been expensive.”
After the discovery Mr Willan had to report the find the NSW Office of Environment and Heritage as well as the federal government’s Australian Hydrographic Service, which maintains and produces navigational charts.
Photos: Damien Siviero