Board member and volunteer skipper Tim Buckley said the unit was just under $100,000 short of the $440,000 it needed for the "stripped down, basic version'' of the Warren & Mahoney-designed building.
The unit's board had taken "backwards and forward steps'' in the past few months as funding promises expired and others were renewed, which meant the project had to be retendered in a time of high building-cost inflation.
"We've ended up in a situation of chasing shadows. The money we've got in hand probably would have built the place 18 months ago.''
Now operating from a storage shed at the back of a Scouts building at Frankton Marina, the unit was granted consent in 2012 to lease a vacant neighbouring site for the build.
The new base will house rescue equipment, serve as an operations base during search and rescue missions and be a training centre for community boating and water safety courses.
Mr Buckley said that after three years of fundraising, the unit's 18 volunteers were "chomping at the bit'' to get the build started.
The unit provided a service equivalent to volunteer fire brigades, St John and LandSAR, so he hoped the community would help it raise the remaining funds.
Major contributors so far are the Central Lakes Trust with $250,000, the Community Trust of Southland with $42,000 and the estate of former Lake Hayes resident Peter Wilding, which contributed $50,000.
The unit had also been offered a $50,000 interest-free loan by the Queenstown Lakes District Council, although it was considering applying for the loan to be converted to a grant.
Funds already raised by volunteers would cover the costs of consultants, consents and administration, so all funds from external sources would be dedicated to the build, he said.
