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What is "Phantom Float"

29 replies [Last post]
Thu, 2009-03-12 12:42
Francis Aborot
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When I explore the internet, I encountered Phantom Float term... Its not clear for me, but I want to develop my skills in planning...Pls help me...

When I develop a plan, my problem is how to minimize total float but maintaining the proper logic specially in high-rise building where the links between floors is not allowed. When I used resource leveling, it gives me stange result and I cannot control the activities itself... How to develop a baseline plan which is theoretically and contractually valid while maintaining it to be a workable program for the site people.

Pls. email me, thanks: francis_planning@yahoo.com
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Replies

Tue, 2009-03-17 05:31
#1
Safak Vural
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Dear Sirs,

My syggestion about manual resource leveling is introducing the crews in to the job. Neither CLIENT nor CONTRACTOR(maybe not) will allow some crews to sit over in the site and do nothing. You can create some dummy links and activities that you can explain to your managers by detailing of the crews that are going to complete the tasks (I know that I am writing the description of resource levelling!). You will need to hear your site engineer or construction managaer about what they are going to do in real. Anyway you need to do this for everything in your plan also.

Regards,

Safak
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Mon, 2009-03-16 09:14
#2
R. Catalan
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Francis,

I suggests that you go back to the basics of planning & scheduling and actual P/S practices that works on site to improve your P/S techniques.

- realistic scheduling parameters (proper links, logic, etc.)
- limitations of duration to 2 weeks or less (easy to track - good practice)
- effective tracking and control of work constraints (materials, labor, shop drawings, etc.)
- make sure that night shifts are allowed in the contract (Contractor side)
- and other day to day effective project management

I agree with the Planner that some activities have no primary links between floors like FF Blockworks is not dependent to GF Blockworks, finishes, etc.. But other activities should have FS link between floors (i.e. concrete works, MEP, External Envelope,..)

Cheers,
R. Catalan
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Sat, 2009-03-14 01:30
#3
Charleston-Joseph...
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In conclusion,

Phantom Float as i surf in the net is only a technical description derive from the mind of someone who got pressure to come up with something to justify his leisure hours and post in some technical and/or professional magazine.

It has no meaning in day to day and practical activities of planer, planning keyboard jockeys. It will only complicate the lives of above average planning and scheduling engineers.

Company and consultant will not go to that extent of looking for phantom float because it is just a waste of time and money.

Nobody takes it seriouly, also the author hence it never reach the mainstream of planning and scheduling activities.

Cheers,
Happy Planning and Scheduling
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Fri, 2009-03-13 11:37
#4
Francis Aborot
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Hi Se,

The result of global financial crisis is catastrophic... The origin of this discussion will not come into this level when there is no crisis... Arguments of project management team boils down to the purpose of holding any payment and giving to contractor the fault if there is delay....

Good Relations with the client is not enough....

Thnx and more power,
Francis
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Fri, 2009-03-13 11:22
#5
Se de Leon
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Understandably, consultant should protect the client. But, unreasonably protecting the client to me, is a contractual issue. There is such thing as onerous provisions in the contract. This is one of those.

IMHO
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Fri, 2009-03-13 11:09
#6
Francis Aborot
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Hi Se,

The intention of the owner representative is clear,,,,JUST PROTECT THE CLIENT at any cause... Thats why you know, Im suffering from doing multiple plans for different use... I have the following...

1. Contractual Schedule
2. Site Construction Schedule- where I used soft logic and resource movement....
3. Management Schedule- Head Office

I also have Progress %

A. Owners Representative
B. Site Monitoring and Control

Thnx and more power,
Francis
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Fri, 2009-03-13 11:03
#7
Stephen Devaux
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If soft logic is used, however, it is crucial to compute its DRAG and relate it back to the bottlenecked resource that the soft logic was input to obviate. Otherwise we will continue to confute work logic delays with resource availability delays.

Francis, I don’t know how to get rid of float -- I only know that by far the best way to justify additional resources is to compute the dollars of delay cost caused by the resource bottleneck and compare it to the cost of resolving the bottleneck with additional resources.

Finally, there is, in theory, absolutely NO difference between theory and practice!

(Unfortunately, in practice there often is a difference.)

Fraternally in PM,

Steve Devaux
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Fri, 2009-03-13 10:56
#8
Se de Leon
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Hi Francis,

Your consultant considers floor to floor logic as soft link. So what would stop him from telling you to allocate resources to all floors at the same time? that’s why mike described it as ludicrous. This is the problem when consultants can interfere in the means and methods of the contractor.

Check again what your contract says. Or maybe check your original intent when you bidded for the project.

Perhaps this is one of those instances when consultants get too far.
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Fri, 2009-03-13 10:45
#9
Francis Aborot
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Hi Mike,

But how can you explain that it is best to plaster(GF) after you plaster(1F)...It is soft logic...Sorry if Im so detailed, but they allow logical links at all and perform the program of unlimited resources in accordance to our contract conditions.

Any more bright ideas?

Anyway, this section is all about Phantom Floats...

Thnx and more power,
Francis
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Fri, 2009-03-13 10:45
#10
Vladimir Liberzon
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Hi Mike,
I still do not believe in manual levelling but in any case if the schedule does not include existing links/constraints then it could not be used.
Soft logic usually describes some management decisions like what direction of work will be selected - from the right to the left or vice versa. And these decisions shall be taken into account. I do not call these links as resource driven.
It is useful to create several scenarios (work from the right to the left, from the left to the right, etc.) and choose the best. But some soft logic shall be selected.
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Fri, 2009-03-13 10:22
#11
Mike Testro
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Hi All

Lets keep it simple shall we.

A properly prepared and resource modelled programme will have one critical path through the activities and one set of total float.

Resources can be levelled manually - Vladimir and I had a spirited discussion on this topic sometime back - and then monitored.

Any delay to the project will then cause a change in the critical path and available float.

The base of the problem is that programmes are not linked up proerly.

Francis has the ludicrous situation where the employers engineer refuses to allow resource driven links between structure levels - just tell him to get stuffed and do it properly.

I don’t know how Newton got into this discussion but my philosophy is based on the principal that it is best to plaster a wall before you paint it - otherwise the plaster drops off.

Best regards

Mike Testro
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Fri, 2009-03-13 10:18
#12
Vladimir Liberzon
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If resources are limited then you shall rely on resource-constrained schedule and resource-constrained floats. RCS drives the dates in realistic manner – if you have only two cranes then your schedule shall take it into consideration. If CPM schedule suggests to use 10 cranes simultaneously then this shall be called unrealistic. And there is no reason to regret that this unrealistic schedule will be destroyed by applying real life constraints.

Variability of resource numbers and productivities may be covered by risk simulation, creating different project scenarios and adding project buffers. I think that this is separate theme.

Regards,
Vladimir
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Fri, 2009-03-13 10:06
#13
Francis Aborot
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Hi Vladimir,

CPM and float is very clear in Management Science....Im sorry if I mislead you with my words float issue....What Im trying to express is my desire to reduce the floats of activities expecially in high-rise construction industry...

In a project where strict guidelines is being implemented, e.g. the use of soft logic like link of work packages between floors is not allowed (Only hard logic or logical link) and resource leveling is being inspired, excessive floats will be encountered in CPM. RCS techniques gives a different value of floats and will drive the dates of activities in an unrealistic manner... As one of our colleague here said, it will distroy your schedule in nanosecond once you perform RCS...In my view, yes, because resources no. and productivity is extremely variable...

So what’s the solution?...That’s why Mr.Se said, an explosion of new theories rise.......

Thnx and more power,
Francis

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Fri, 2009-03-13 10:01
#14
Se de Leon
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That’s why it’s called theory. Maybe in the near future I we’ll find the Newton among us here in PP. But so far, everything about scheduling is just theory and best practices.
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Fri, 2009-03-13 09:47
#15
Francis Aborot
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Hi Se,

You are correct.. But even though there is an explosion of new theories around the world, researchers, programmers, and planners find it difficult to integrate those theories in a software. And if they do so, sometimes theoretical in nature and too hard to execute, manage, and maintain in a real world setting....


Thnx and more power,
Francis
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Fri, 2009-03-13 09:44
#16
Vladimir Liberzon
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Hi Francis,
what do you mwan by float issue?
Resource Constrained float has nothing common with CPM total float.
Activities that were critical in CPM schedule may have floats in resource-constrained schedule, activities with total floats in CPM schedule may become critical in resource-constrained schedule.
I never met phantom float and do not understand its definition.
Best Regards,
Vladimir
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Fri, 2009-03-13 09:37
#17
Se de Leon
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I think this is the result of having an imperfect system in using scheduling techniques like CPM and Earned Value Analysis. The result is, an explosion of scheduling theorists around the world. I guess this is one of those terms that sounded very strange when you hear it first but when you come to realize it, you already know it but maybe defined in another way.

Google it, and you will find that there is such thing as Phantom Float.
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Fri, 2009-03-13 06:48
#18
Francis Aborot
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Hi Stephen,

Do you have other technique to resolve float issue?..other than resource leveling?.....

Thnx and more power,
Francis
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Fri, 2009-03-13 06:39
#19
Stephen Devaux
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Francis wrote:

"According to my understanding, SOMEBODY CORRECT ME IF IM WRONG, the difference of CPM Float and RCS Float is called Phantom Float... If anybody has a high level understanding, please discuss."

Francis, I’ve never heard of phantom float, so I don’t know what the difference between CPM Float and RCS Float. But the difference between CPM DRAG and RCS DRAG is a very important metric! In Total Project Control, it’s called Resource Availability DRAG. RAD is the amount that the project is being delayed from its CPM completion date by resource unavailability.

In TPC, the idea is that, as much as possible, we’d like to separate delays in the CPM schedule (delays due to Newtonian physics, if you will) from delays due to lack of resource availability. It’s a LOT easier to change availability than it is to change Newtonian physics!

Obviously, sometimes the resource critical path will be different from the CPM CP due to resource delays. The cost to the project (in schedule incentives, marching army costs, etc.) due to completion delays caused by resource unavailability can be tied to specific resources, and is the Cost of Leveling with Unresolved Bottlenecks.

In turn, the CLUB is a dollar (euro?) figure that you can use to justify the cost of the additional resource(s) to reduce the resource availability DRAG.

Fraternally in PM,

Steve D.
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Fri, 2009-03-13 04:08
#20
Francis Aborot
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Hi Mike,

Honestly I dont know Phantom Float.. But I found out only in the internet site at the research library of the American Society of Civil Engineers when I was looking on the ways on how to minimize total float without compromizing the logical relations of activities..

It suggested to have the Resource-Constrained Scheduling (RCS) technique which is resource leveling instead of the classic Critical Path Method (CPM) neglecting the effect of limited resource which is realistically and theoretically correct. But Obviously resulted in strange result specially if your using computer containing thousands of activities. According to my understanding, SOMEBODY CORRECT ME IF IM WRONG, the difference of CPM Float and RCS Float is called Phantom Float... If anybody has a high level understanding, please discuss.

Please, If somebody has a great technique in optimizing scheduling procedure, please advise.

email me at
francis_planning@yahoo.com


Thanx and more power,
Francis
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Fri, 2009-03-13 03:25
#21
Mike Testro
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Hi Francis

If you know what it is will you please tell the rest of us.

Best regards

Mike Testro
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Fri, 2009-03-13 01:33
#22
Francis Aborot
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Hi charles,

No, Im serious, Phantom Float is a project management term...

Thanx,
Francis
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Thu, 2009-03-12 19:42
#23
Charleston-Joseph...
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Francis,

I have not encountered this word.

I did work in Dubai and it could be similar to the beautiful bridge along the Dubai Creek:

Floating Bridge.

Cheers,
Happy Planning and Scheduling
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Thu, 2009-03-12 17:01
#24
Francis Aborot
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Hi Mike,

Thanx for the advise,
Anyway, I open your training aid but the PDF opens blank...

Regards,
Francis
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Thu, 2009-03-12 16:42
#25
Mike Testro
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Hi Francis

You are in a very difficult situation.

I would suggest that you resort to manual resource levelling - this is a method the I use in PowerProject software and is probably suitable for for other types.

This is a section of a paper that I submitted to the CIOB as part of their "Best Practice Guide to Time Management"

Best regards

Mike Testro.

5. Resource Levelling
5.1 Operating by Software.
5.1.1 Just because the software has a facility to produce a resource levelled programme it is not guaranteed that it will produce the required result.
5.1.2 To put it simply – Never Use It because:
1. When you press the button you have no control over what is happening.
2. It will distort the programme more radically and quicker than any unsupervised trainee scheduler on day release can hope to achieve.
3. It will take an age to discover what changes have been made.
5.1.3 If you are going to do a resource levelling exercise it is quicker and safer to do it manually with total control of the exercise.
5.2 Manual Resource Levelling
5.2.1 The main reasons for levelling resources are to:
1. Smooth out peaks and troughs.
2. Eliminate over deployment.
5.2.2 One method of carrying out a manual resource levelling operation is to start with the first work package on the programme and:
1. Set up a view of the project showing:
1.1 A filtered view of the Work Package tasks.
1.2 The available Total Float.
1.3 The planned gang size.
1.4 The resource histogram showing:
1.4.1 Peaks and troughs
1.4.2 Over deployment as a red band.
5.2.3 First select the tasks that are contributing to the Over Deployment and reduce the gang size.
5.2.4 Reschedule and check the available float and effect on the histogram.
5.2.5 Continue until the Over Deployment has been eliminated.
5.2.6 If the tasks turn critical before the Over Deployment has been eliminated then:
1. Review the criteria that set the maximum deployment.
2. Consider a logic adjustment to create more float.
3. Consider a resource adjustment in other work packages to create more float for this package.
5.2.7 If none of these options are available or effective then prepare for a contract over run.
5.2.8 When all the Over Deployment has been dealt with do a similar exercise to level out the peaks and troughs.
5.2.9 Continue the exercise until all work packages have been dealt with.
5.2.10 It is good practice to review the changes from the first package so that further adjustments can be made if necessary
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Thu, 2009-03-12 16:13
#26
Francis Aborot
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In our contract, it states unlimited resource.. There is no way he will approved the plan unless I perform resource leveling... Or any other method available?... Or else, the floats in activities will go extremely large which is not realistic for site execution.. His argument is this, only logical links are allow, meaning hard logic.. Personally, I don’t like resource leveling because I can’t manage it properly in thousands of activities..
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Thu, 2009-03-12 16:02
#27
Mike Testro
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Hi Francis

Your consultants planning engineer is just plain WRONG.

If your programme has a limited resource of blocklayers then the only way to level the reource is to link between floors.

Unless this requirement is written into your contract then you are not required to follow this unreasonable dictat.

Regarding phantom float being related to the difference between a resourced driven programme and a FS driven CP then again if each activity is properly resource modelled then the two systems will work together - giving one result.

Phantom float is just that - a figment of the imagination brought about by ignorance of reality.

Please keep in touch.

Best reagrds

Mike Testro
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Thu, 2009-03-12 14:49
#28
Francis Aborot
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Hello Mike,

Links between floors are not allowed according to our consultant’s planning engineer.

For example

GF Block work ----> 1F Block work relations is not allowed..

ABOUT PHANTOM FLOAT.

According to my source in the internet is the following.

a resource-constrained critical path method (RCPM) technique that capitalizes on and improves the existing critical path method (CPM) and resource-constrained scheduling (RCS) techniques. A traditional CPM schedule is not realistic, because it assumes unlimited resources, some of which are highly limited in practice. Although traditional RCS techniques can consider resource limitations, they do not provide the correct floats and critical path, as the CPM does. The difference between the theoretical remaining total float and the real remaining total float is referred to as "phantom float"

Thanks,
Francis
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Thu, 2009-03-12 14:24
#29
Mike Testro
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Hi Francis

Why do you say links between floors is not allowed?

My advice regarding resource levelling is Never - Ever use the software it will screw up your project in nanoseconds.

Go and have a look at the training section - you may be interested in my Bottom Up worked example of a concrete structure.

As regards Phantom Float i have never geard the term before but I can imagine that it is something like excessive float that springs up when a link is missing.

Every activity must have at least 1 outgoing link to some other activity.

Best regards

Mike Testro
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