Stability of crane carriers

Vital Sparks
17th March 2011, 13:33
Having just seen one of the Zhen-hua fleet deliver a goliath crane to Rosyth dockyard would be possible for someone to explain (without difficult sums) why they don't roll over. I'm assuming this is one of those counter intuitive situations. See below for a typical example

http://www.shipsnostalgia.com/gallery/showphoto.php/photo/228248/title/zhen-hua-19/cat/518

lazyjohn
17th March 2011, 15:15
I guess correct ballasting, wide hull extensions, good weather routing and not filling the counter balance boxes.

I have worked with heavy lift ships but no loads like that one.

It a funny old world when its cheaper to transport this stuff, than to build it on site.

lakercapt
17th March 2011, 16:03
One of my other concerns would be how do you see where you are going and how the radars would operate.
Bet they had sleepless nights on board that ship!!!

lazyjohn
17th March 2011, 16:51
See what you mean about visibilty.

I sailed on a passenger ship recently where every cabin had a tv. One channel showed the view from the bridge. Would that sort of thing be allowed for manouvering?

The foremast has lots of gear on it but I can't recognise a radar scanner.

Billieboy
17th March 2011, 17:29
Weather routing!

Nick Balls
17th March 2011, 17:29
cr*p design should be the other way around, like dockwise vessels with the accommodation and bridge forward.

Clanline
17th March 2011, 19:57
It is made of polystyrene so is as light as a feather!

Supergoods
17th March 2011, 20:58
The basic issue with this type of vessel is that they are designed to carry a maximum load on deck and still be stable.
As you say intuitively she would be very tender however with a crane load the opposite is usually the case.
With the Ocean America on the Blue Marlin the cargo weight was about 31000 tons and the VCG above the base of the rig was about 27M.
The GM of the vessel as loaded was about 26M so if anything we were a little too stiff for comfort rounding the Cape of Good Hope.
It certainly made the good ole oilfield boys review their behavior in this world and their proximity to the next.
Ian

Hawkeye
18th March 2011, 03:23
The Zhen-Hua ships are converted tankers, so the accomadation was already aft. As a result, they kept the ballasting arrangement for use with the transportation of these cranes. But they were underpowered. One was blown aground from the anchorage of the Hook of Holland some time ago, with cranes aboard. Another one was threatened with bad weather in an anchorage of Felixstowe, so with the previous grounding in mind, they bought her into the port, only for her to break the moorings and ground in the harbour, again with cranes onboard. In this case, there was a lot of damage done to the cranes already there, two of which collapsed when the cranes on the ship hit them.
I'm sure these two had small lookout posts forward of the cargo decks, which would have been manned when loaded. I can't see this on this ship.

chadburn
18th March 2011, 13:40
Is the lookout post not the box shaped structure just behind the guard rail's on the fo'c'sle.

Clanline
19th March 2011, 13:44
It does look like some sort of lookout post on the fos'c'le and there could possibly be a radar on the foremast too.

I bet the cargo played merry hell with the magnetic compass!

Supergoods
19th March 2011, 15:18
I bet the cargo played merry hell with the magnetic compass!

As does any large steel object when carried as cargo.
I question wether anyone, apart from Port State Inspectors, cares if the magnetic compass is usable any more
Ian

Clanline
20th March 2011, 08:11
True enough Ian about the compass, we did not bother with them except to enter it in the log!
That is apart from one ship I was on(Roxburgh Castle) which did not have a gyro so it was all magnetic compass and hand steering!

On most of the ships I sailed on I don't remember having much problems with steel cargo affecting the compasses as mostly the distance from the cargo to the compass was quite a bit wheras those cranes are almost on top of it!

Supergoods
20th March 2011, 12:43
Yes, I remember Brocklebanks Maihar was also Magnetic Compass only when I sailed on her in 1960.

If I remember my compass theory, the magnetic field of the ship was created by the fact that the ship in th builders yard was kept on a fixed heading for a long period and aquired its magnetic field due in some part to the hammering of the riveters.

Modern ship construction which is all welded with major sections being completed on different headings may result in a weaker ship magnetic field than in ships built by traditional methods.

The large deck cargo pieces, be they cranes, oil rigs or industrial process modules may have aquired a more specific magnetic field than the smaller heavy lifts handled in earlier times.

Ian