There are multiple museum ships you can explore in Los Angeles from the Queen Mary oceanliner to the USS Iowa Battleship, as well as several nautical and maritime museums that focus on different aspects of the life of a mariner and seafaring technologies over time and the age-old tradition of model ship building.
The Queen Mary Attraction and Hotel in Long Beach, CA is a floating museum that interprets the ship's history as a luxury ocean liner and a war transport ship during WWII. The ship also hosts short-term and long-term traveling exhibits. In addition to the exhibits, the Queen Mary operates as a hotel, with multiple shops, restaurants and nightlife options.
Scorpion Russian Foxtrot Submarine
The Scorpion Russian Submarine is located adjacent to the Queen Mary and can be visited as a combo ticket with the Queen Mary or on its own. It's a self-guided audio tour that is not handicapped accessible. You have to be able to climb down the hatch to visit.
The SS Lane Victory is a WWII merchant cargo ship located in San Pedro, CA, operated as a museum ship by the United States Merchant Marine Veterans of World War II. The cargo holds of the ship now contain museum exhibits on the life of a mariner as well as the tools used by sailors in the 1940s.
USS Iowa Battleship Museum
The USS Iowa Battleship Museum is located at Berth 87 at the LA Waterfront in San Pedro, CA. The ship served as a US battleship from 1940 to 1990 from WWII through the Persian Gulf War. The museum is operated by the Pacific Battleship Center.
Los Angeles Maritime Museum
The Los Angeles Maritime Museum is located in the former Municipal Ferry Terminal building on the San Pedro waterfront near Ports O' Call Village. The museum has photos and artifacts from the USS Los Angeles as well as exhibits on commercial diving and the areas cannery history.
Southern California has a dozen historic and replica Tall Ships from Oxnard to San Diego, some of which can only be admired from shore. Others offer tours or weekend sails to the public. Additional Tall Ships from other ports visit LA harbors every year for various special events and battle reenactments.
Since you're here looking at the list of museum ships and maritime museums, I thought you might be interested in getting out on the water yourself, so here's a list of LA area boat tours, ferries and cruises.
I don't normally list things that are in San Diego since it's about a 2-hour drive from Los Angeles, but for ship fans, the biggest collection of ships from Navy vessels to tall ships that you can visit all in one place in Southern California is at the San Diego Maritime Museum.