posted 10-31-2009 10:04 PM ET (US)            

http://www.woodenboat.com/forum/showthread.php?t=99253

posted 11-01-2009 05:38 AM ET (US)         

This company dockwise moves some stuff like this 59500 tonne semi-submersible, the overhangs are at least 40ft and the whole vessel is sunk to offload the semi-submersible cargo

http://www2.dockwise.com/projects/node/432

posted 11-01-2009 09:23 AM ET (US)            

I know they rely heavily on stabilization systems. In the past these stabilization systems were huge retractable gyro controlled and hydraulically powered fins which stuck out at an angle from the curve of the hull.

We had a smaller version of these on our somewhat "topheavy" Hatteras 58 cruising boat and they reduced roll about 80% but did not eliminate it. Of course this type of system is useless unless the vessel has boat speed through the water. The speed required is a function of how large the fins are and how "tall" the vessel is. These cruise ships have several sets of very huge fins.

I'd like to know more about the stabilization systems on the latest cruise ships like the one you are referring to. Have they come up with systems that don't require forward motion? Also what are the operational limits as to sea state?

Are they mandated to avoid forecast wave height of a certain magnitude?

What would happen if one of these ugly monsters lost all ability to power ahead and got caught in the troughs of some rogue waves in a storm?

Maybe there is a marine architect on this site who can help discuss this interesting question

posted 11-01-2009 09:28 AM ET (US)            

You sure got that right, Jim. UHHGGGG-LEEEEEEE!

posted 11-01-2009 09:52 AM ET (US)            

Although these ships appear to look top heavy, the effect is counteracted by weight of the machinery and tankage mounted low in the ship, in addition, ballast tanks are also incorporated into the design to ensure stability.

(I do this for a living, so this is not opinion, its fact)

Much like an Aircraft Carrier, that also looks "top heavy", it seems that there is more "mass" above the waterline than there is below, but the lowest point in the ship is called the "Tank Top", when you look into the "bilge", especially on very large ships, you are not seeing the actual bottom shell plating of the hull, but the top of ship service tanks that reside above the keel.

These tanks are fuel, black water (sewage), gray water (bath and sink)and seawater ballast tanks, and run the entire length of the hull. The volume of these tanks, in conjunction with the machinery spaces provide enough longintudinal stability to offset the structure above the main deck. In addition, fluid transfer systems are installed to direct fluids of each of these tanks to maintain stability as these fluids are generated (waste water) and consumed (fuel, freshwater) to maintain the required stablilty.

posted 11-01-2009 01:27 PM ET (US)            

Can you comment on whether the "safety envelope" (again, sorry for the lay term) of these new cruise ships is different from other vessels, such as a tanker or bulk carrier when those are loaded?

posted 11-01-2009 04:50 PM ET (US)            

I`ve never been on a cruise ship before. It arrives in Florida in November for its maiden trip. It would take a seven day cruise just to walk around this ship. One of the video`s comments thats not long enough to visit all the restaurants on board.

posted 11-01-2009 08:52 PM ET (US)         

I think you mean vertical centre of bouyancy and not longitudinal or even transverse centre of bouyancy.

They all have an effect on the overall stability (pitch, roll heave etc etc) of the vessel but as we are talking top heavy it's the vertical thats the most important.

As further the total mass CoG is below the displacement CoG at a given draft, the greater the stability, generally and excluding any additional bilge keels and external stabilisers.

Although the total lightship mass and CoG may well be quite high when the total global ship mass and CoG is calculated which includes all the operating and ballast loading this can be considerably lower.

I too do this for a living and I am resposible for these calculations although the dynamics are not done by me.

As a point of interest many aircraft carriers and sub marines carry a considerable ammount (100's of tonnes) of concrete and/or lead ballast in thier keels to ensure there is a sufficent negative differential between the total mass CoG and the displacement CoG, this is what gives the righting bouyancy and stability.

This is why in my example by Diockwise that is carring 59.500 Tonnes is offset by several 100,000 tones of mass below the waterline by ballast

It looks wrong but it works

Regards
Steve

posted 11-02-2009 01:01 AM ET (US)         

Correct the loading plan and design will be tailored for it's intended cruising ground

All ships have an incluning experiment which enables you to verify the CoG.

This is achieved by calculating the deadload mass and CoG plus a ballast plan.

The LCG and TCG can then be back calculated from the draft marks.

To get the VCG by adding a known weight (concrete/lead blocks)to the port then to staboard and recording the draft marks around the ship for each case the VCG CoG can be verified.

posted 11-02-2009 10:06 AM ET (US)            

Steve, I stand corrected, I meant to say "Vertical Center of Buoyancy" vice Logitudinal.

Capt. Jim, you are also correct in that there is a distinct difference between a "Cruise" ship (e.g. Carnival) vice a full sea-going vessel, a Liner, such as the QM II.

As such, these hulls are designed differently for sea-states for which they are anticipated to operate in. The vessel being discussed here seems to me like she will be used in the cruise market, much like a Carnival ship. (Steve, please correct me here if I'm mistaken).

Boat Dryver, vessels such as tankers and bulk carriers are designed much the same way most other large vessels are, based on their intended service.
Once this is established, the factor of safety is determined around one emperical design factor, and that is known as the full load waterline for commercial ships and full combat water line for military vessels. Once these parameters have been determined, the factor of safety is then "compounded" into the intial design calulations in order to ensure a sufficient factor of safety. In other words, the ship is designed for the "worst case scenerio" (full tanks, max. loading, and maximum intended sea-state, then the factor of safety is derived once this has been determined)

posted 11-02-2009 08:29 PM ET (US)         

No problem :)

dnh

Yes the VCG is high but this is the compromise you pay for having decent radar defelectors on board :) ( Sorry in advance Jim)

posted 11-02-2009 11:52 PM ET (US)            

Based on the rated 4500 gallons of #2 diesel fuel burn rate per hour at cruise (30mph?) that works out to 1 gallon of fuel every 45' of travel.
Just a little worst then my 23 Conquest with a 225 Merc hanging off the transom.

By the way this Royal Caribbean cruise ship has an amazing combined 30,000 hp in the bow thrusters alone.

posted 11-03-2009 12:16 AM ET (US)            

quote:

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Does this Zodiak look topheavy based on the passenger's center of bouyancy?
http://continuouswave.com/whaler/images/suzukiDF60TwinCams.jpg

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posted 11-05-2009 12:20 PM ET (US)            

Year Built 2009
Tonnage 220,000 tons
Registry Bahamas
Length 1,181 feet
Beam 154 feet
Passenger Capacity 5,400
Crew Size 2,150
Total Inside Cabins 496
Total Outside Cabins 2,210
Cabins & Suites w/ verandas 1,956
Suites 166

To compare to the newest Nimitz Class carrier: USS George H. W. Bush