This is probably more than you wanted to know, but it this excerpt, from about.com, will enlighten us all. The names don't do much for me either but.....
In the over 130-year-history of Holland America Line, there are many traditions and practices. When the ms Zuiderdam, ms Oosterdam, ms Westerdam, and ms Noordam entered service they carried on the storied tradition of naming passenger ships with the "dam" suffix. Coupled with the "dam" ending has been a famous river, mountain, sea, city or town and often directional bearings.
Holland America ship names also draw from the historic log of ship names, allowing the company to bridge its past with its future growth. The Zuiderdam, Oosterdam, Westerdam, and Noordam respectively named for the south, east, west, and north points of the compass are no exceptions.
The first vessel with the "Zuider" prefix launched in 1912 as the cargo ship Zuiderdijk ("dijk" or "dyk" was the suffix used for cargo vessels; "dam" is used for passenger ships). At 5,211 tons, she sailed between Rotterdam and Savannah, Georgia, for Holland America through 1922, with a brief stint during World War I as a transport.
In 1941, the 12,150-ton Zuiderdam was launched from a shipyard in Rotterdam for outfitting. However, a month later the ship was damaged during a British air raid and capsized. The hull was raised and later sunk by the Germans to block the port of Rotterdam to Allied access. After World War II, the Zuiderdam was again raised, yet the ship never saw completion.
The only ship to bear the "Ooster" prefix was the 8,251-ton, one-prop Oosterdijk. She began service in 1913, also sailing from Rotterdam to Savannah. During World War I, the ship served the Allied war effort.
The second Westerdam sailed on 643 voyages for Holland America Line during a career spanning more than 13 years with the company.
The ship, which began service as the former Home Lines' Homeric in 1986, was named the Westerdam and officially entered service with Holland America Line on Nov. 12, 1988.
The Westerdam's arrival expanded the fleet to four ships and signaled the beginning of a new era of growth for Holland America that continues today. In 1989, the Westerdam underwent a notable $84 million renovation at the Meyer Werft shipyard in Papenburg, Germany, where it was originally built. During an extended drydock, it was "stretched" by a then-cruise industry record 130 feet, increasing its capacity 1,000 to 1,494 guests and its size from 42,000 gross tons to 53,872.
After carrying more than a million guests on Caribbean, Panama Canal and Alaska cruises, the ship left the Holland America fleet on March 10, 2002, transferred to sister company Costa Cruises, where it continued its career cruising European waters as the Costa Europa.
The first Westerdam sailed for Holland America Line from 1946 to 1965. A combined cargo/passenger ship, with five cargo holds and accommodations for 143 first-class passengers and 126 crewmembers, the ship made the Atlantic crossing twice a month between Rotterdam, The Netherlands, and New York City. The 12,149-gross-ton, twin-propeller ship and its sister ship, Noordam II, took eight days to make the crossing.
The Westerdam was a survivor of three sinkings during World War II before it ever made its maiden voyage.
Its keel was laid in Rotterdam on Sept. 1, 1939, at the Wilton Feyenoord Shipyard, but construction was suspended when the Germans invaded Holland in 1940. On Aug. 27, 1942, the half-completed ship was bombed by Allied forces at its berth and sunk. German troops raised the ship, but in September 1944, it was sunk by Dutch underground resistance forces. Raised again by the Germans, it was sunk for the third time by the Dutch underground on Jan. 17, 1945.
After the war, the Westerdam was raised by the Dutch and construction was completed. On June 28, 1946, the Westerdam departed Rotterdam on its maiden voyage to New York. It continued regular trans-Atlantic service until it was sold to Spain for scrap on Feb. 4, 1965.
The newest Noordam is the fourth Holland America ship to bear this name. The previous Noordam III had sailed for the fleet since 1984. In 2005, the Noordam III was sold to Louis Cruise Lines, which chartered her to Thomson Cruises.
The latest Zuiderdam arrived in December 2002, followed by the Oosterdam in July of 2003. The Westerdam was delivered in spring 2004, and the Noordam completed the compass points in February 2006.