Dear bottle2480,

The efficiency of a grab crane can be represented by: actual capacity/theoretical capacity.

or,

GrabCraneEfficiency = (actual travel distance * actual grab velocity) / (theoretical travel distance * theoretical grab velocity * volumetric usage of grab)

Investigating the terms in the formula will lead to a the factor, which is hampering your tts capacity.

Travel distance of grab:

Is the operator maneuvering the grab over the shortest distance?

(Hoisting, slewing, luffing at the same time. This is called square operating or round operating)

Actual grab velocity.

Is the operator using the highest possible winch speeds and accelerations without any waiting time?

(Aggressively controlling the machinery will speed up the unloading operation, providing that this behavior does not cause damage to the crane nor the ship)

Volumetric usage of the grab.

Is the operator able to fill the grab to the maximum load as much as possible?

Over loading the grab and then opening the grab a little to decrease the grab load, causes loss of cycle time and reduces the grab crane efficiency by reducing the overall grab velocity.

In the clean-up phase, this factor is very much depending on the auxiliary clean-up equipment and the use of that equipment in combination with the clean-up strategy and the skill of the operators.

Other influencing factors are the type of ship and the nature of the unloaded commodity.

In short:

Investigate where time is lost and where the equipment is not fully used to its limits.

Divide the unloading process (closing grab, hoisting grab, slewing, luffing, opening grab and return to hold) and check the efficiency of these steps separately.

Perform this investigation for the various phases of the unloading process. (free digging, clean-up, shifting, mobilizing and de-mobilizing clean-up equipment, etc.)

Also check the mechanical condition of the grab crane.

Modern cranes have PLC controllers to take care of the grab movements from the moment of lifted above the hatch coaming to the material dump and back to just above the hatch coaming, where the operator takes over again for filling the grab again.

A grab crane performance is made by the crane operator in combination with the clean-up operators.

Consult well-known crane builders.

Have a nice day

Teus ■

Hi bottle2480,

Teus said everything already.

Maybe you should check also how the "rated capacity" of the ship-unloader was calculated, especially with what kind of grab type?

There are different grab types and some types are faster and more effective, some less.

This could explain at least a part of the missing capacity...

But keep in mind that all calculations are theory...

Regards

Sigvard ■

Originally Posted by Sigvard

Hi bottle2480,

Teus said everything already.

Maybe you should check also how the "rated capacity" of the ship-unloader was calculated, especially with what kind of grab type?

There are different grab types and some types are faster and more effective, some less.

This could explain at least a part of the missing capacity...

But keep in mind that all calculations are theory...

Regards

Sigvard

Dear Friends,

The ship unloader capacity is a hot subject.

This forum has discussed this subject earlier also. Pl go through earlier correspondences in this forum.

Normally for coal, clam-shell type grab is used.

The efficiency as per JIS standard is 50% to 60% depending upon many factors,main one is Size of the Ship,Parcel size etc.

Achieving 50% is not that difficult,going above 50% requires lot of care and input.

In modern unloaders,except grabbing all activities are PLC controlled-automatic.

An experienced operator can give better out put by trying to achieve maximum out put.

At least 60% of the cargo unloading should be at rated capacity.

Balance can be as follows,

25% at 50% rated capacity and balance 15% at 20%rated capacity.

A lot of time can be saved by adopting best mopping of last 15% use good and sufficient numbers of equipments for last clean up

Rgds,

Narayanan Nalinakshan. ■

Were you satisfied with the tender value?

Can you find out who approved it?

How long did it take for the shortcoming to appear? (Should have been inside the handover period.)

According to the example figure in the previous thread it should be possible to load out at 54% efficiency. (With a lot of care and input because >50%)

If you are experiencing a 20% shortfall despite attempted remedies throughout and beyond handover then there is reason to question the procurement process.

Would you care to name names or keep quiet, struggle on and forget it?

When you modify the unloader you have to unload the next available ship and the demurrage cost can go either way. ■

Efficiency can be 100% and you can still end up with an inadequate machine. What you are really after is tonnage. h

Besides, How does the Jap standard account for standing walls? These can play havoc when the shovels are called in at the bottom of the holds.

Lets take a dig at unloading.

On the subject of standing walls who decides how they were formed? Are they assumed to be remote from the loading process in which case the additional demurrage might be to the shippers account? It is difficult to justify charging the importer for demurrage if the cargo was declared safely loaded and then a tight shipping schedule produced a rough voyage and the cargo became partly consolidated. Nevertheless the importer must recompense the shipper or so it seems. What flexibility covers such cases?

What's the meaning of this reply? Well, if your import contract contained the right small print perhaps you could blame unloading delays on the shipper and so avoid paying out. Then you wouldn't have to worry about your truly meaningless unloader efficiency after all. ■

Originally Posted by johngateley

Efficiency can be 100% and you can still end up with an inadequate machine. What you are really after is tonnage. h

Besides, How does the Jap standard account for standing walls? These can play havoc when the shovels are called in at the bottom of the holds.

Lets take a dig at unloading.

On the subject of standing walls who decides how they were formed? Are they assumed to be remote from the loading process in which case the additional demurrage might be to the shippers account? It is difficult to justify charging the importer for demurrage if the cargo was declared safely loaded and then a tight shipping schedule produced a rough voyage and the cargo became partly consolidated. Nevertheless the importer must recompense the shipper or so it seems. What flexibility covers such cases?

What's the meaning of this reply? Well, if your import contract contained the right small print perhaps you could blame unloading delays on the shipper and so avoid paying out. Then you wouldn't have to worry about your truly meaningless unloader efficiency after all.

First I thought I will ignore this,

I have also have few years of experience in material handling in Ports (47 years) and have handled many ,many ships with all sorts of equipments.

When some one asked for achievable efficiency,I have given my latest experiences. Nothing more. I don't like to reply if you have any other sarcastic remarks.

For your kind information,in modern Indian Ports all stevedoring activities are the responsibility of the Port,demurrage and despatch are to the account of the Port.

With best Regards,

Narayanan Nalinakshan. ■

I fail to see sarcasm by suggesting that efficiency is meaningless if the machine itself is inadequate. It was simply implied that an achieved distance at an achieved speed with a full bucket gives 100% efficiency and yet the machine still cannot do the job as promised in the tender specification.

My comment on standing walls is quite reasonable and I plead the case that an importer should not be automatically charged demurrage when the cargo is unsuitable due to shipping factors beyond his control. Personally I would prefer to see unloading times rewarded with bonuses. Indian shipping business practice is not my concern. In fact no shipping practice concerns me. I just see things for what they are or could be.

Finally, my criticism of the relevance of efficiency and the accuracy of the procurement procedure was directed to the thread starter, still is and is valid and well intended. I don't like to see folk worried by what they can't change. Especially if they are not really responsible in the first place. ■

Originally Posted by johngateley

I fail to see sarcasm by suggesting that efficiency is meaningless if the machine itself is inadequate. It was simply implied that an achieved distance at an achieved speed with a full bucket gives 100% efficiency and yet the machine still cannot do the job as promised in the tender specification.

My comment on standing walls is quite reasonable and I plead the case that an importer should not be automatically charged demurrage when the cargo is unsuitable due to shipping factors beyond his control. Personally I would prefer to see unloading times rewarded with bonuses. Indian shipping business practice is not my concern. In fact no shipping practice concerns me. I just see things for what they are or could be.

Finally, my criticism of the relevance of efficiency and the accuracy of the procurement procedure was directed to the thread starter, still is and is valid and well intended. I don't like to see folk worried by what they can't change. Especially if they are not really responsible in the first place.

Thank you Sir,

I agree to your experience on standing walls.

Let us impart the lessons we have learned, toiling so many years with bulk material handling, to the new comers and less experienced engineers.

With due Regards,

Narayanan Nalinakshan. ■

Originally Posted by Teus Tuinenburg

Dear bottle2480,

The efficiency of a grab crane can be represented by: actual capacity/theoretical capacity.

or,

GrabCraneEfficiency = (actual travel distance * actual grab velocity) / (theoretical travel distance * theoretical grab velocity * volumetric usage of grab)

Investigating the terms in the formula will lead to a the factor, which is hampering your tts capacity.

Travel distance of grab:

Is the operator maneuvering the grab over the shortest distance?

(Hoisting, slewing, luffing at the same time. This is called square operating or round operating)

Actual grab velocity.

Is the operator using the highest possible winch speeds and accelerations without any waiting time?

(Aggressively controlling the machinery will speed up the unloading operation, providing that this behavior does not cause damage to the crane nor the ship)

Volumetric usage of the grab.

Is the operator able to fill the grab to the maximum load as much as possible?

Over loading the grab and then opening the grab a little to decrease the grab load, causes loss of cycle time and reduces the grab crane efficiency by reducing the overall grab velocity.

In the clean-up phase, this factor is very much depending on the auxiliary clean-up equipment and the use of that equipment in combination with the clean-up strategy and the skill of the operators.

Other influencing factors are the type of ship and the nature of the unloaded commodity.

In short:

Investigate where time is lost and where the equipment is not fully used to its limits.

Divide the unloading process (closing grab, hoisting grab, slewing, luffing, opening grab and return to hold) and check the efficiency of these steps separately.

Perform this investigation for the various phases of the unloading process. (free digging, clean-up, shifting, mobilizing and de-mobilizing clean-up equipment, etc.)

Also check the mechanical condition of the grab crane.

Modern cranes have PLC controllers to take care of the grab movements from the moment of lifted above the hatch coaming to the material dump and back to just above the hatch coaming, where the operator takes over again for filling the grab again.

A grab crane performance is made by the crane operator in combination with the clean-up operators.

Consult well-known crane builders.

Have a nice day

Teus

Dear Mr Teus

Sir

We have planned to use level luffing crane with unbuilt hopper for coal unloading . There is general perception that level luffing crane gives efficiency 45%

I understand , in unloading process there is loss of time and cycle. Would you please list out the all interuption to be considered between rated capacity and average capacity

RB ■

Originally Posted by NarayananNalinakshan

Dear Friends,

The ship unloader capacity is a hot subject.

This forum has discussed this subject earlier also. Pl go through earlier correspondences in this forum.

Normally for coal, clam-shell type grab is used.

The efficiency as per JIS standard is 50% to 60% depending upon many factors,main one is Size of the Ship,Parcel size etc.

Achieving 50% is not that difficult,going above 50% requires lot of care and input.

In modern unloaders,except grabbing all activities are PLC controlled-automatic.

An experienced operator can give better out put by trying to achieve maximum out put.

At least 60% of the cargo unloading should be at rated capacity.

Balance can be as follows,

25% at 50% rated capacity and balance 15% at 20%rated capacity.

A lot of time can be saved by adopting best mopping of last 15% use good and sufficient numbers of equipments for last clean up

Rgds,

Narayanan Nalinakshan.

Dear Mr Narayanan Nalinakshan

You have referred to JIS standered , would you please forward the same to my mail ID chaubey.07@gmail.com ?

Further , would you explain all the interruption to be considered to arrive efficiency ?

You told A lot of time can be saved by adopting best mopping of last 15% use good and sufficient numbers of equipments for last clean up , would you suggest , what measure shall be take to meet this provision ?? ■

Dear Teus,

I appreciate you for giving detailed explanation of the problems of this material handling world on this Forum. You know in India, most of the time,the selection of such a critical items done on the basis of cost and the commercial guys has their final say at the time of finalization of orders.At the time of placing order,their main job is to save money and make BIG BOSS happy. Serious technical discussions takes place/ starts after the equipment gets in to action.

Anil Seth

QUOTE=Teus Tuinenburg;78824]Dear bottle2480,

The efficiency of a grab crane can be represented by: actual capacity/theoretical capacity.

or,

GrabCraneEfficiency = (actual travel distance * actual grab velocity) / (theoretical travel distance * theoretical grab velocity * volumetric usage of grab)

Investigating the terms in the formula will lead to a the factor, which is hampering your tts capacity.

Travel distance of grab:

Is the operator maneuvering the grab over the shortest distance?

(Hoisting, slewing, luffing at the same time. This is called square operating or round operating)

Actual grab velocity.

Is the operator using the highest possible winch speeds and accelerations without any waiting time?

(Aggressively controlling the machinery will speed up the unloading operation, providing that this behavior does not cause damage to the crane nor the ship)

Volumetric usage of the grab.

Is the operator able to fill the grab to the maximum load as much as possible?

Over loading the grab and then opening the grab a little to decrease the grab load, causes loss of cycle time and reduces the grab crane efficiency by reducing the overall grab velocity.

In the clean-up phase, this factor is very much depending on the auxiliary clean-up equipment and the use of that equipment in combination with the clean-up strategy and the skill of the operators.

Other influencing factors are the type of ship and the nature of the unloaded commodity.

In short:

Investigate where time is lost and where the equipment is not fully used to its limits.

Divide the unloading process (closing grab, hoisting grab, slewing, luffing, opening grab and return to hold) and check the efficiency of these steps separately.

Perform this investigation for the various phases of the unloading process. (free digging, clean-up, shifting, mobilizing and de-mobilizing clean-up equipment, etc.)

Also check the mechanical condition of the grab crane.

Modern cranes have PLC controllers to take care of the grab movements from the moment of lifted above the hatch coaming to the material dump and back to just above the hatch coaming, where the operator takes over again for filling the grab again.

A grab crane performance is made by the crane operator in combination with the clean-up operators.

Consult well-known crane builders.

Have a nice day

Teus[/QUOTE] ■