Big cruise lines are increasingly requiring passengers to pick a boarding time in hopes of streamlining embarkation on large ships.

The idea is to offer a smoother, more tranquil first day onboard.

In the past year, Carnival Cruise Line, Royal Caribbean International and Norwegian Cruise Line have all rolled out staggered check-ins on some or all of their ships.

Norwegian is the furthest along. Last June, it began enabling guests on the 4,000-passenger Norwegian Breakaway to select their arrival time when they downloaded documents as part of the online check-in process. Guests select a half-hour window to board between 11 a.m. and 3 p.m. The line continued to expand the idea to its other ships; by November, almost anyone on a Norwegian ship departing from a U.S. port was able to take advantage of staggered check-in.

The only exceptions are Norwegian’s Hawaii-based Pride of America, due to later departure times, and its Anchorage/Seward itinerary because of cruise-tour complexities.

Carnival says it strictly enforces the staggered times and will ask guests to return to the terminal later if they show up early. Norwegian is less strict.

Carnival’s version started last year in Galveston, Texas. The line extended it to two of its New Orleans-based ships, the Carnival Elation and Carnival Dream, and is targeting Miami next, beginning March 4. The Carnival Triumph, also based in New Orleans, is scheduled to begin staggered check-in this April.

Royal Caribbean’s staggered check-in program is currently limited to the Anthem of the Seas. Royal assigns arrival times, rather than enabling guests to choose.

Andy Stuart, president of Norwegian, said staggered check-in helps break up the “big block” of passengers who tend to arrive around noon.

Stuart said that so far the idea has been a qualified success: “I won’t say it’s perfect; I think it’s improved it. It has started to spread people out a little more effectively.”

One important difference between Carnival and Norwegian is the policing of early arrivals. Carnival says it strictly enforces the staggered times and will ask guests to return to the terminal later if they show up early.

However, if guests show up later than their assigned times, “we allow them to come in and check in,” Carnival spokesman Vance Gulliksen said.

Norwegian is less strict, Stuart said. “We don’t force anyone to sit and wait. People embark as quickly as we can get them on,” he said.

“There are people who are rule keepers,” Stuart continued. “They say ‘OK, I was told to arrive between 11 and 11:30, and that’s what I’m going to do.’ And then there are rule breakers who say, ‘I don’t care what you tell me; I’m going to get there for lunch.’ So we like the rule keepers, but we don’t penalize the rule breakers.”

Stuart said Norwegian is working on other ways to speed the process of embarkation.

“Nobody books the trip to be on the embarkation; they book the trip to be on the ship,” he said. “We think investments in technology and automation to accelerate the process will continue to improve that experience.”