Cornwall's National Maritime Museum has launched an appeal to raise £4m over the next 10 years.
The museum in Falmouth, which opened in 2004, receives no government funding, although in the past it has been awarded EU and lottery money.
It attracts more than 100,000 visitors a year and employs about 20 full and part-time staff.
A banquet to launch the appeal and mark the museum's 10th anniversary was attended by Princess Anne.
Spokeswoman Tamsin Loveless said it was the Princess Royal's fourth visit to the museum.
"She's a good friend to the museum and we're very fortunate to have her support," she said.
The museum contributes nearly £5m a year to the local economy, Ms Loveless added.