The Merchant Marine Act of 1920, which is also known as the Jones Act, prohibits foreign-flagged ships from embarking and disembarking passengers in U.S. ports unless they call in another country on the way. Because it’s much less expensive to register ships in countries other than the U.S., nearly all cruise vessels these days are foreign flagged. So they can’t embark passengers in Seattle and disembark them in Alaska, unless they stop in Canada.

That’s why most Alaska cruises, and most Alaska repositioning cruises, begin or end in Vancouver. Which isn’t a bad thing. Vancouver is one of the most beautiful, vibrant cities in the world. And this year, it’s getting a facelift for the 2010 Winter Olympics.

One of the nice things about Alaska repositioning cruises is you can usually find one that suits your needs. They range in length from 3 to 20 days. And you can often disembark in more than one port. Because the shorter sailings are often sold at a very deep discount — fares as low as $99 per person aren’t unheard of — they’re also a good way for first-time cruisers to “test the waters.”

Holland America repositioning cruises to Alaska.

On April 18, 2010, Holland America’s Ryndam leaves Tampa on a 21-day voyage to Vancouver. She calls at Grand Cayman and Columbia before transiting the Panama Canal. After passing through the canal, she visits Costa Rica, four ports in Mexico, San Diego, and Victoria before arriving in Vancouver on May 9. With a two-level dining room, an exhibition kitchen with plasma TV monitors, and just 1,266 passengers, Ryndam is a lovely place to spend three weeks. Passengers can also embark in San Diego on May 5 for a four-night cruise.

Holland America fans who don’t have much time for vacation can board their Zaandam in San Diego on April 21, 2010. En route to Vancouver, she calls at Catalina Island, Astoria, Oregon, and Victoria, BC. During the days at sea, passengers can enjoy a pool with a retractable roof, a jogging track, tennis and volleyball courts, and the Ocean Spa. With fares starting at just $399 per person, it works out to less than $135 per couple, per day.

Ryndam’s sister ship, Statendam, sails from Fort Lauderdale on April 25, 2010 and calls at Aruba before entering and crossing the Panama Canal. After that, she visits Costa Rica, Guatemala, four ports in Mexico, and San Diego, before ending the voyage in Vancouver on May 16. A 26-foot splashing fountain in the three-story atrium greets passengers as they board. Those with less time can board in San Diego on May 12.

Cruisers who love days at sea can join Holland America’s Amsterdam in Los Angeles on April 29, spend three nights aboard and disembark in Vancouver on May 2nd. The 1,380-passenger Amsterdam is a sister ship to the Rotterdam.

On May 4, 2010, the 1,918-passenger Zuiderdam sails from San Diego to Vancouver. Passengers can disembark in Vancouver four days later. But those who want to see Alaska can remain aboard and cruise the Tracy Arm, and then visit Juneau, Skagway, Glacier Bay, and Ketchikan before leaving the ship when it returns to Vancouver on May 15.

Princess Cruises repositioning cruises to Alaska.

Coral Princess is 1,974-passenger cruise ship with a demonstration kitchen, a ceramics lab, and a swimming pool with a retractable dome roof. She sails from Fort Lauderdale on April 21, 2010 and transits the Panama Canal, arriving in Vancouver on May 10. As an alternative, passengers can board in Los Angeles on May 6, call at Victoria, BC on May 9, and arrives in Vancouver the next day. This four-night getaway is a nice break for west coast cruisers, and with fares from $349, it’s very affordable.

The 2,600-passenger Golden Princess has four pools, nine whirlpools, an adults-only Sanctuary, 17 lounges, and more than 700 balcony staterooms. She sails from Los Angeles on May 9, overnights at Catalina Island, and visits San Francisco, and Victoria before ending in Vancouver on May 14.

Royal Caribbean repositioning cruises to Alaska.

Sailing from the opposite direction, Royal Caribbean’s Rhapsody of the Seas sails from Honolulu on April 27, 2010. She spends two full days in Maui and then visits Kona and Hilo on the Big Island before crossing the Pacific en route to Vancouver. Five days at sea give passengers plenty of time to enjoy the spa, fitness center, and rock climbing wall. Special deals for California residents start as low as $899.

On May 8, Radiance of the Seas sails up the west coast from San Diego to San Francisco. After a couple of days at sea, she visits Ketchikan, Juneau, Skagway, Hubbard Glacier, and Sitka in Alaska, and then Nanaimo and Victoria in British Columbia. Passengers leave the vessel in Vancouver on May 21.

Because of the Merchant Marine Act of 1920, also known as the Jones Act, cruises that originate in U.S. ports cannot end in U.S. ports unless another country is visited.  As a result, Alaska cruises that begin in the U.S. usually end in Canada, and vice versa.

Vancouver is the departure port for most cruises that end in Alaska.  And it’s the city of departure for most repositioning cruises leaving Alaska at the end of the season.

Many Vancouver repositioning cruises can be taken for different lengths of time.  You can take a 3-night cruise aboard the Coral Princess from Vancouver to Los Angeles,  with no stops in between.  Or, you could stay on board, transit the Panama Canal, and disembark 18 nights later in Fort Lauderdale.

Perhaps the least expensive cruise ever is the three-night cruise aboard the Sapphire Princess from Vancouver to Los Angeles.  Inside cabins for this late September sailing are going for as little as $99.  And you can upgrade to a balcony stateroom for  $100 more.

Princess also offers a 17-night cruise from Vancouver to Fort Lauderdale aboard the Island Princess.  This relatively small ship — 1,900 passengers — offers 24-hour buffet, bistro, and room service.  Three restaurants serve steaks, Italian, and Cajun food.  And the Sanctuary Spa provides a relaxing retreat.

The ship calls at San Francisco, and several ports in Mexico, Costa Rica, Panama, Columbia, and Aruba, before arriving in Fort Lauderdale.

Royal Caribbean’s Serenade of the Seas goes north to Alaska before heading down the coast for San Diego.

After visiting Sitka, Juneau, Skagway, and Ketchikan, the Serenade calls at Seattle, Astoria, Oregon, and San Francisco before arriving in San Diego two weeks later.  Fares start around $100 per night.

Those who want to try cruising without spending much money can put their toe in the water on Norwegian’s 7-night cruise from Vancouver to Los Angeles.   One of the least expensive repositioning cruises out there, fares aboard the Norwegian Star start at just $349.

Guests aboard the Norwegian Pearl can sail from Vancouver to Los Angeles in five nights, or  travel down the Mexican coast and through the Panama Canal to Miami in nineteen nights.  Because of the popularity of Panama Canal cruises, this voyage isn’t the bargain that many others are.

The Big Daddy of all repositioning cruises from Alaska is aboard Holland America Line’s Volendam.  The ships leaves Vancouver in late September and arrives in Hong Kong 46 days later.  En route, you’ll call at six ports in Japan, South Korea, seven ports in China, and three in Viet Nam.  What’s more, the ship overnights in Tokyo, Beijing, and Shanghai.

With  twenty sea days, there’s plenty of time to relax and enjoy the amenities aboard the ship. If you have the time, this is a great itinerary.  And fares are currently about 50% off the rack rate.

Find out about Panama Canal cruises here.