Load cells in cranes - Ian Rogers, maybe you could...

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atferrari

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Load cells in cranes.

When for any reason the cargo runner (the wire lifting the hook) in a crane, is not pulling in the actual vertical direction (as in the case commonly found when working in 2-cranes lift modality) do the load cell sense the higher component involved or just the true weight?

This question comes from the so many times that when handling weights with vessel's equipment, as I said, in 2-cranes lift, Ch. Officers complain that the weight is higher than declared.

I started to suspect that the laod cells are actually detecting the (obviously higher) component when the wire is not in the exact vertical.

Ian, maybe you could chime in?
 
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That depends where your measuring... It you are monitoring the line pull ( the wire lifting the hook ) Then No... The weight felt on the wire rope is the true weight PLUS any friction and the acceleration of the weight..

What tends to happen on port side cranes when they are offloading / loading the ships... The weight ( say 32 tonnes ) will feel like 40 tonnes as the acceleration of the sidewards movement is felt...

When we monitor the load... I have to factor in the friction and any acceleration.. so the weight seems stable... Trouble with that is... The crane IS being overloaded at that point.

Drivers, especially those on piecework, whine when the alarms sound when operating the cranes.... The fact is that this EXTRA force does break the cranes....
The weight displayed will be correct.

If the load is sensed by moment.... That's a different story. This gives an accurate measure of the load lifted.

If two cranes are used... Theoretically they share the total load EVEN if the wire rope isn't vertical... The force is always in the direction of the wire rope.

Sorry scratch that!!! With TWO cranes there will be a lower reading on each if the wire isn't vertical..... (Not much though)
 
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You've got me thinking now........ How much off the vertical are you talking!! up to 10 degrees! Or more?
 
Ian

I have to disagree with some of that.

The force (tension) in a single crane wire which is making a vertical lift will be

F = mg + ma

where
F = force in Newtons
m = mass of the load in kilogrammes
a = acceleration of the load in m.s^-2
g = acceleration due to gravity (9.81m.s^-2)

If two cranes are sharing the load equally with vertical lift wires, the force in each wire will be
F = (mg + ma)/2

If the two cranes are sharing the load equally with lift wires at an angle θ (same angle on both crane wires), the force in each crane wire will be
F = (mg + ma)/(2 x Cosθ)

If the wires are at an angle of 60 degrees to the vertical, the force in the wires will be double (ie x2).

JimB
 
Jim... Sorry I should have updated my stance..... I have been PM'ing Atferrari... I was talking about one crane using two winches... Two cranes is a different matter... If the wires ARE at 60° ... Get the hell out of there.... A vertical deflection of 10° is 2% more than the load... I hate myself for doing the thing I tell other not to do.... Keep it in the forum.

Of course your loadings add up..... In our business we stay clear of tandem lifts if possible..
 
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If the wires ARE at 60° ... Get the hell out of there....
Click to expand...
Just a numerical example!
If I saw that in real life, what steps would I take?
Bloody great big ones in the opposite direction!

Tandem lift?
Bread and butter in the offshore oil industry.
How about this bad boy:


JimB
 
I find the lift very impressive.... I have seen quite a few GOOD lifts the most impressive wasn't the heaviest....

Baldwins have a 1200 tonne crane... but we erected it on an airstrip down in Lincolnshire ( near Grantham ) The test lift was only 40 tonne but it was around 300 meters away, we drove from hook block to the drivers cab.... The test lift was for a job in Sellafield nuclear power station...
 
Hola Ian,

Thanks for replying.

I know that the component for a wire pulling out of the vertical is higher.

So you confirm my suspicion: the load cell senses higher value thus the display in the driver's cabin shows more than expected.

For me, in the activity with project cargo vessels, some of them with cranes of up to 450 MT SWL, 2-cranes lift is common. But never with the cargo runners out of the vertical what should be immediately corrected.

BTW, (few) multipurpose vessels have their cranes on starboard side, what for the uniformed soul could make to berth the lady on the wrong side. Seen that a few times already. (It happens mostly with vessels chartered for a voyage only where the operator doesn't realize that cranes are "on the other side").
 
Additional questions, Ian

I have ships in mind here.

1) What precision could I expect in common cranes for the weight as shown in the display?

There are vessels with a big size display showing weight (MT) and outreach, visible from inside the holds. Very useful.

2) Do you know any technique to know how much is the cargo runner out of the vertical?

Gracias for your time.
 
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We get around 300kg for cranes up to 35 -40 tonne... @1 tonne for cranes around the 100 tonne mark..

What is your ADC precision?

When we make displays for dry docks... You need an angle sensor to gauge the angle of the wire ropes that cradle the boat for different widths.
Perhaps you could do the same...
 
Ian Rogers said:
We get around 300kg for cranes up to 35 -40 tonne... @1 tonne for cranes around the 100 tonne mark.
Click to expand...

Impressive. How do you calibrate a load cell for hundreds of tonnes? Not easy to carry the testing weight with you, I guess

Ian Rogers said:
You need an angle sensor to gauge the angle of the wire ropes that cradle the boat for different widths.
Click to expand...

Ian, I am an interested frequent user, not intending to develope anything of real size but eventually, a small model for a proof of concept. How this angle sensor could be implemented in a small model (tabletop scale)?

Additional comment: When working with a Danish Supercargo at Punta Quilla (Argentina) discharging project cargo, we discussed how to minimize the "out of the vertical" condition of cargo runners in 2-cranes lift. He told me that somewhere in Europe they did some attempts using a laser pointing downwards but the results were not good.
 
If the loads are large... ie over 10 tonnes we have the customer supply a known weight ( they need to take it to a weigh bridge ) if the crane is small we have 10 tonne load links to cal with...
 
Thanks for replying Ian.

Could you say something about the question below? Gracias!

atferrari said:
Ian, I am an interested frequent user, not intending to develope anything of real size but eventually, a small model for a proof of concept. How this angle sensor could be implemented in a small model (tabletop scale)?
Click to expand...
 
There are small angle sensors available on electronic wholesale sites.... I buy from RS components... small SOIC devices that suits my needs... A tad expensive for ""One Off's" though.

Search inclinometers...
 
I run mobiles and crawler cranes for the past 18yrs now.
In that time I've noticed that despite the planning done until its on the hook no-one can be absolutely certain what loads will be attained.
Two crane picks ,generally, are planned as not to load either crane more than 75%.In this fashion,dynamic loading ,out of plumb loading,pushing ,pulling can be accounted for as extra load.
If its only going straight up and down with both cranes free,the worst of the loading is if one crane gets ahead of the other ,as the load tilts the crane on the high side gets more load.
Now where a two crane pick requires the load to be swung,its generally the two operators that decide which crane is pulling and which crane is pushing,both cranes are in free swing ,when one crane comes around it takes the other crane naturally, at the height of the swing the second crane will boom down or up and the first crane finishes its swing and chase's the load ..
hope you get the jest ,,but its kind of hard to describe feel and experience,theres alot of things happening at once,and staying on top of them all,its like conducting an orchestra
what needs to be avoided neither crane is being dragged(holding the swing brake),this can add up to a lot of extra weight ,fast,
 
@ More coffee.... I used to work for Loadwise ( you must have heard of them )... They did a controlled lift in Scotland... Four cranes (Lampson's) Rolling an Oil rig.... This was before wireless.... We ran cables from each crane to a central hub, so the foreman could oversee the lift!!! Once we had it up and running... Some numbty rolled an excavator through all the wiring..... Caused days of upset!!!
 

Hola MC,

All my experience was made in vessels. In some ports it is me who conducts the operation.

There, the sole thing I leave sometimes to the more experienced drivers is to correct the out of plumb condition by themselves.

There is a port where the driver of each crane changes every 75 minutes. Tere are 14 guys in the list. Since I use their name and not the crane's, keeping in mind who's where at any step of the handling is a good excercise to keep Alzheimer away...

In other port, where I work most of my time, the two best drivers work alone without exchanging a single word.

I just tell them the initial precautions I like to take prior lifting and that's all to it.

Vessels add the extra concern of the listing as you swing. Anti-heeling systems not always
work properly.

Anxiety in all this doesn't count for me, and yes, the feeling is nice!

BTW, now I know what is the name (in English) of a crawler crane... (wondered that for years).

Be well.
 
Its an interesting day,but you guys are absolutely right, seasoned operators can usually set the load anywhere you want just show them where the load is and where you would like to see it put, all a signal person really should have to do is watch tolerances if the load is tight to an obstruction and finalize the final resting place.

Ian Rogers
Ive heard of Loadwise, and Lampsons,,were you guys using transilift's...by the way when its four cranes on the load its no longer a pick its ballet
 
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