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Ever marvel at how exactly ships float? It seems impossible, considering today's cruise ships are gigantic steel-encased cities carrying thousands of passengers and crew, not to mention tons of food, fuel, water, poker chips, bingo cards, pizza pies, beer bottles, lobster tails, and some, even rock climbing walls and billiards tables.

To get technical for a few moments, according to Archimedes' principle, a ship floats because it's hollow and its total weight is equal to the weight of the water displaced at a given draft. A ship sinks when it's heavier than the water it's displacing. It's obviously crucial for the naval architects who build ships to understand all of this. Especially considering all the wacky features being designed for new cruise ships these days -- giant hot tubs and bowling alleys to name just a few -- weight issues are a naval architect's biggest challenge and a ship's weight is constantly being estimated throughout the building process.

Fuel and water, for example, take up an enormous amount of weight. A ship like the 160,000-ton Liberty of the Seas, for example, hauls along about 2,500 tons of fuel at the start of a 7-night cruise and consumes about 1,500 tons of water each day.

In case you're taking notes, keep in mind there are various ways to measure the weight and carrying capacity of a vessel. The lightweight is the actual weight of the ship itself, completely empty, without cargo, fuel, ballast, fresh water, food, drinks, passengers, crew and baggage. According to my sources, the total lightweight of Royal Caribbean's Liberty of the Seas, for example, is about 60,000 tons. On the other hand, the ship's deadweight tonnage is the actual weight of the cargo (fuel oil, fresh water, diesel oil etc), passengers and crew and so on -- it's the difference between the lightweight and total displacement weight. This would be about 10,000 tons at the start of a week-long cruise on Liberty of the Seas. However, the standard measure of a ship's size quoted more often is its gross registered tonnage, or grt. The longer, wider and higher a ship's hull and superstructure are, the more volume it has and the higher its grt will be. Generally, a gross ton is approximately equal to one hundred cubic feet of space enclosed.

Once seaworthy, a ship's weight is balanced and stability is maintained by moving ballast around. Typically, ballast takes the form of tanks of sea water and fuel that can be pumped in and out of different locations in the bilge (the bottom of the vessel) to keep a ship on, as they say, an even keel.

Are you still awake? The point is, cruise ships are darn big these days and they can sure hold a lot of stuff.

Currently, the biggest ships topping 100,000grt are:

Freedom and Liberty of the Seas (www.royalcaribbean.com)

  • 160,000grt, 3,634 passengers double occupancy.
  • Over-the-top features: outdoor water park, full-sized boxing ring, surfing simulator, and a pair of over-sized hot tubs cantilevered 20 feet out over the side of the ship.
  • Another sister coming in 2008, Independence of the Seas.

Voyager, Explorer, Adventure, Navigator and Mariner of the Seas (www.royalcaribbean.com)

  • 142,000grt, 3,114 passengers double occupancy.
  • Over-the-top features: ice-skating rink, rock-climbing wall, miniature golf course.

Diamond and Sapphire Princess (www.princesscruises.com)

  • 116,000grt, 2,670 passengers double occupancy.
  • Over-the-top features: miniature golf course.

Caribbean, Crown and Emerald Princess (www.princesscruises.com)

  • 113,000grt, 3,100/3,080 passengers double occupancy.
  • Over-the-top features: giant outdoor video screen; also, a private sundeck with a $15 cover charge called The Sanctuary has lounge chairs, trees, and private cabanas for quiet cocktails or massages.

Costa Concordia and Serena (www.costacruises.com)

  • 112,000grt, 3,000 passengers double occupancy.
  • Over-the-top features: a high-tech Grand Prix driving simulator.
  • Another sister coming in 2009.

Carnival Conquest, Glory, Valor, Liberty and Freedom (www.carnival.com)

  • 110,000grt, 2,974 passengers double occupancy.
  • Over-the-top features: huge kids and teens facilities, plus a giant video screen on the pool deck.

Grand, Golden and Star Princess (www.princesscruises.com)

  • 109,000grt, 2,600 passengers double occupancy.
  • Over-the-top features: private teen sunbathing deck; giant video screen on deck (Grand).

Costa Fortuna and Magica (www.costacruises.com)

  • 105,000grt, 2,720 passengers double occupancy.

These giants will soon be plying the oceans and seas:

Carnival Splendour (www.carnival.com)

  • 112,000grt, 3,006 passengers double occupancy.
  • Over-the-top features: water park and humongous kids facilities.
  • Slated to debut in late 2008, 2009 and 2010.

Fantasia and Serenata (www.msccruises.com)

  • 133,500grt, 3,300 passengers double occupancy.
  • Over-the-top features: water park and humongous kids facilities.
  • Slated to debut in late 2008 and 2009.

Solstice, Equinox & Eclipse (www.celebritycruises.com)

  • 118,000grt, 2,850 passengers double occupancy.
  • Over-the-top features: water park and humongous kids facilities.
  • Slated to debut in late 2008.

Project Genesis (www.royalcaribbean.com)

  • 220,000grt, 5,400 passengers double occupancy.
  • Slated to debut in late 2009.

Unnamed NCL pair (www.ncl.com)

  • 150,000grt, 4,200 passengers double occupancy.
  • Slated to debut in 2009 and 2010, with option for third sister in 2011.

Carnival Dream and Magic (www.carnival.com)

  • 130,000grt.
  • To debut in 2009 and 2011.

Unnamed Disney pair (www.disneycruiseline.com)

  • 122,000grt.
  • Slated to debut in 2011 and 2012.

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