A group of Sea Cadets were unable to get a new front door for their hut because companies were too scared to venture on to their island.
Northampton Sea Cadets is based in the middle of the river Nene and its 35-year-old front door was rusted, uninsulated and storm-damaged.
Three door companies refused to quote "due to access and health and safety concerns", Lt Chris Read said.
Northampton University campus workers have now supplied a door for free.
Lt Read said: "Problems with getting to the site means we have difficulties having large materials delivered, or if a company says it can deliver, the price rises significantly so it's out of our reach."
He contacted the University of Northampton which is in the final stages of building its new £330m Waterside Campus across the Nene from Calves Holme Island.
Campus builders Bowmer & Kirkland offered to supply and fit the door for free, despite the "tricky access".
Lt Read said the 130 cadets were "very grateful" and its hut is now "more secure and welcoming".
The Sea Cadets is a maritime charity for young people aged between 10 and 18.