How Big Is It?

One other thing that is done on a sea trial is to actually measure the physical size of the ship. For a cruise ship, the most important measure is not its weight or the weight of its cargo, but the space available onboard. And just to confuse matters, space is measured as “gross registered tons” or “grt”. The history is interesting, at least to me.

Originally, a key measure of the carrying capacity of a ship was not how much it weighed, but how much space it had available for cargo. And a common cargo was wine, which was shipped in large casks called “tuns”. A tun held 8 barrels of wine or about 242 gallons. Soon they started measuring the area onboard based on how many of these boxes or tuns you could fit in. Thus, a ship that could transport 8,000 barrels of wine was known as a 1,000 tun ship. “Tun” evolved into “ton” and then into “Gross Registered Ton”. To give you a sense of scale, Clipper Ships in the mid-1800’s were built ranging in size from 400 grt to 4,000 grt.¹

The advent of steel hulled ships and steam engines allowed them to build larger and larger vessels with the Titanic measuring a whopping 48,000 grt. Aircraft carriers have to be particularly large, and today aircraft carriers measure as large as 100,000 grt. Imagine if all that space were filled with wine.

And then there is Oasis of the Seas. Our original designs called for Oasis to be a little over 200,000 grt. Early additions quickly increased this to about 220,000 tons but these were just early estimates. One of the duties of the classification society is to measure the actual space onboard the ship and to certify its grt. DNV performed its preliminary calculations during the sea trial and calculated that the grt of Oasis of the Seas is closer to 225,000 grt. This is slightly higher than estimated, but well within the expected margin of error for such estimates. This figure is still preliminary and isn’t final until DNV finish their measurements and calculations closer to delivery.

All this is why shipping people cringe when someone says that a particular ship “weighs this many gross tons.” There are other measures of a ship’s weight, the most relevant of which are:

Lightweight Tons The easiest measure to explain is the lightweight tonnage. This is simply the physical weight of the ship when it is light i.e. with no cargo onboard. If you could pick up the ship and put it on a scale, what would she weigh? This measurement is not particularly relevant to most ships and is mainly used to calculate how much steel the yard needs to build the ship and the value of the scrap steel at the end of a ship’s life. The lightweight of Oasis is about 88,600 lwt.

Deadweight Tons The deadweight tonnage of a ship is mainly used for cargo ships and is a measure of how much cargo the ship can carry by weight. Thus a 50,000 dwt coal carrier can carry about 50,000 tons of coal. To be precise, it’s slightly less than 50,000 tons because the ship’s fuel, water, crew, etc. are also considered cargo for this purpose and have to be deducted to calculate how much cargo the ship can carry.

On a cruise ship, the numbers are dramatically less then for cargo ships. For cruise ships, the “cargo” is mainly the fuel and the water that the ship carries. Passengers and crew as well as luggage and musical instruments are trivial. The deadweight tonnage of Oasis of the Seas is 17,100 dwt, most of which is allocated to fuel and water. Interestingly, this is much more deadweight capacity than we need but this gives us a cushion for changes. For example, if we put a heavy sculpture on the top deck, this would cause a reduction in the ship’s deadweight. By designing the ship with “surplus” deadweight, we have more room for such changes.

¹ Although a tun is simply a measure of volume (about 100 cubic feet), there is a connection to measures of weight. A tun of wine holds 242 gallons which weighs about 2,240 pounds. The English developed something called a “long ton” which is also 2,240 lbs. Thus, if you filled up a 700 tun ship with wine, the cargo would also weigh 700 long tons.

14 Responses to “How Big Is It?”

  1. RCL4ever says:

    What about the horn??? Did u all create a “new” horn like the Queen Mary 2 for the world’s new largest passenger vessel?


  2. Per Arne says:

    Thanks for the interesting historical background to the ton. For me it’s great to see that you are not only the CEO of a cruise line, but obviously have a real appreciation of ships. Maybe that’s why Royal Caribbean has some of the most handsome ships afloat today; not only floating versions of Las Vegas but ships that honor maritime tradition. Keep up the good work and thanks for sharing it with us on this blog.


  3. Steve Schrobo says:

    I have been on numerous cruises and my wife and I Diamond members on Royal Caribbean. I also work for the US Navy and have work in the Aircraft Carrier Program Office.
    When the Navy provides “weights” of ships it is in long tons displacement. An aircraft carrier displaces about 102,000 long tons. When asked of your Chief Engineers on your Voyager Class they would displace about 68,000 long tons. Since the weight that you site is a measure of volume your can then stated that your Oasis Class “weights” over 225,000 tons. I am curious – what does the Oasis of the Seas displace in long tons?

    From an article I found on the Internet by Dick Plano, Professor of Physics emeritus, Rutgers University:
    There is no clear definition of displacement and tonnage. The clearest (which may be right) is in “The tonnage of a ship is not a weight, but a volume. One ton is 100 cubic feet. The total internal volume of a ship is its gross tonnage, and if we subtract all the volume not used for cargo, we get the net tonnage.” As for
    displacement, “The total weight of the ship and everything in it is
    the displacement, measured in long tons of 2240 lb. A long ton is only a
    little larger than a metric ton of 1000 kg,but is considerably larger than
    the US short ton of 2000 lb.” Therefore the displacement is the total weight of the ship and contents no matter what units you use!”


  4. 417rogers says:

    Thanks for the info and educational background of “tun”, never knew that. Can’t wait to get on this ship!


  5. barrygibson says:

    Dear Mr.Fain,
    Fascinating…..I thought I knew a lot about ships….have been traveling by sea (from Venezuela to New York, and India to the UK, and later from Africa to the UK) since I was 2 years old…one line was called “The Anchor Line”…….anyway, I never heard the story of the “tun”, and the co-relation of weight of wine to the English Long Ton…..thanks, nice to learn new things.
    I think the Oasis is amazing and HAVE to travel on her.


  6. Anita44 says:

    Very interesting. Thank you so much for sharing these facts. I am always describing the weight of the ship to people because we love sailing on “the big ones”. “The bigger, the better” is what I always say! Now I can impart some knowlege into my description… :-)


  7. Cruiseaholic says:

    I just think that Oasis is going to be “tuns or tons of fun”


  8. leesatiff says:

    Hi! I am interested in becoming a Cruise Director, and I have 15 years of experience in the hospitality industry. I have wanted to be a cruise director since I went on my first cruise ten years ago. I am talented, energetic and very hard working. I have a great resume and I have got what it takes to be the best!
    I have applied for job postings, but I havent gotten anywhere just yet.

    Any thoughts or guidance?

    Tiffany Abrahams


  9. eroller says:

    I just receive the new ALLURE and OASIS OF THE SEAS brochure. Nice job as always! One thing I noticed are the private poolside cabanas are missing from Deck 16. They are no longer on the deck plan or in the poolside renderings.

    What made you change your mind about these?



  10. Hans-Georg says:

    Dear Mr. Chairman,
    I took one of the images from “downloadable images” for my weblog, hope this is ok for you. If you do not agree please let me know and I will remove it.
    There is one point I found in your explanation re. ships measurement to which I do not fully agree:
    May I draw your attention to the fact that you are talking about GRT but since a couple of years this has been changed to GT. As far as I know this is not a change of the name only but even a change in the way of measurement. The figures of GT are much higher than the figures of the old GRT.
    You may correct me if I am wrong.


  11. Texino says:

    I don’t think that the cabañas will ever be found on deck #16


  12. Robkna1 says:

    Great stuff! We are sailing on the Oasis in July, and are very excited! I have a question, rather hoping for a better idea about size. I see that while the tonnage of the Oasis is quite-a-bit more then even your more recent Freedom class, however the actual dimensions seem to be somewhat similiar. Does the minor increases in actual dimensions and adding a few decks make that much more room for almost an additional 2000 guests capacity over the Freedom class? Do you worry about crowded areas of the ship? I remeber my first cruise on the Mariner of the Seas, and thinking that 3000 guests would seem crowded, but suprisingly, it did not feel that way at all. Just wondering if this is a concern. Thanks, and we CAN NOT wait to step foot on this new ship!! Great job!!


  13. “The lightweight of Oasis is about 88,600 lwt” <— so is there 1 ton equal than 1000 kilograms or 2240 lbs. or equal than 2000 lbs or what? thank you. this question is from finland.


  14. Camping says:


    [...]How Big Is It? | chairmans-blog[...]…

Leave a Reply