HMNZS Otago patrols in the Southern Ocean and southwest Pacific, and patrols can last up to three months.
The former Gisborne Girls' High School pupil said she joined the navy in 2009 so she could travel and meet new people.
"I had an auntie who had joined for four years, so she kind of talked me into it, and I haven't looked back.
"I've been to Singapore, Vietnam, Guam, the Philippines, New Caledonia, Antarctica, and heaps of places in Aussie as well."
Ms Keenan has even been to the Rim of the Pacific exercise, the world's largest biennial international maritime warfare exercise, in Hawaii.
The 85m Otago will be berthed from 10am to 4pm at Captain Cook Wharf on Saturday and from 10am to 3pm at Queens Wharf on Sunday. Visitors will be able to take 30- to 40-minute tours of the ship and meet crew members.
During the Anniversary Day Regatta on Monday, the Otago will act as the guard ship.