Barge Crane

[280474]

Dear All,
I have a bidder's document to be reviewed regarding the subject. They offer a barged mounted crane with the following specification :
Barge Dimension = 150' x 50' x 10', draft=4.5' completed with ballast system
Crane = Crawler Manitowoc 4100 (Serial 41383) with LaticeBoom 200T capacity (Boom Length = 150ft and 180ft)

According to its load chart, the crane barge is able to lift safely 42 Tons of load at 45' working radius (150 ft boom length and 76.8 deg angle)with crawler extended.

Looking to the layout of crane barge, actualy the crane is not located at the center of barge. In fact, it is located 1.6 meters from barge center line.

What I need from you guys, if you ever have experience using such as barge mounted crane, please share to answer my question.... is it possible to lift 42T of load at 45’ working radius with that specification and layout..?

Looking forward for your response

 

[StephenA]

To work it out properly, you will need to know the metacentric height of the barge and therefore the C of G of the crane and barge.

It is certainly not overly large (our barge is 60m x 20m) but a lot will depend on where it is working: at sea? calm water? and whether he is lifting 360 degrees.

Is the crane 1.6m from the barge centreline along the short or long axis.

StephenA

 

[280474]

The crane barge will be used at very calm sea water in front of our Dock. It will be used for Loading arm lifting activities with maximum 100 deg lifting scheme. The offset of 1.6m is along the short axis.
My further question, is it valid if I assume that movement center gravity of crane barge due to 1.6m offset can be compensated by water ballast system as long as its trim can be maintained below 5 deg..?

Other thing, is there any rules state that crane must be located at barge center line along short axis..?

regards

 

[280474]

Stephen,
Do you have any sample calculation regarding crane barge stability during lifting ? What is the limitation..? what is the acceptance criteria..?

regards

 

[StephenA]

The critical point with water ballast is that whichever ballast tank is used it must be full. Partially filled tanks are very dangerous as they reduce the metacentric height.

I will check up on the other questions

StephenA

 

[tincan]

Have used similar arrangements. 42T is not too heavy a load. Play with the numbers. At 150 x 50 x 4.5 displacement W = 150(50)(4.5)(64)/2000 = 1,080T. The average pressure on the bottom is 4.5(64) = 288psf. 42T direct loading will increase the displacement an average of 42(4.5)/1080 = 0.175 feet(assuming a uniform loading)
A 42T @ 45'==>3,780,000'-lbs
S = lw^2/6 = 62,500 ft^3
p = M/S = 60.5 psf.

Its not naval arch but you get an idea of the barge capacity. Have seen the front awash during salvage operations (with a calm sea)
Best, Tincan.

 

[StephenA]

5 degrees is about the normal limit for the list, although as tincan says salvage work can be almost anything, although having the front awash would be worrying as the wetted perimeter reduces and hence further load can cause overturning.

If you really want to calculate whether the barge will be stable you need to calculate the position of the metacentre and then the metacentric height. My 1968 Fluid Mechanics for Civil Engineers has the formulae, so I imagine most books would and then it is a simple spreadsheet for all the various weights.

The metacentre is positioned at a distance I /V above the centre of buoyancy where I is the second moment of area of the waterline surface about the central axis and V is the volume of water displaced.

The metacentric height is the distance from the centre of gravity to the metacentre. The metacentre must be above the centre of gravity for stability.

I am not sure how to attach a file to a reply (or even if is possible?) but I could scan the pages if you wish.

StephenA

 

[280474]

Since I has a C.G chart for the specific 4100W series from Manitowoc, I believe the formulae will be very helpful to calculate the crane barge stability at many lifting schemes.

I am very glad if you could scan the pages and send to me via email at nasrul@badaklng.co.id

Thanks in advance.