One of the great tools for schedule management is the analysis by a CPM/PERT network of what will or could happen. Not only does it help in planning, but it gives us information about the impact of schedule changes on the time aspects of a project.
This article is about one of the many kinds of information that can be generated, namely that mysterious and yet wonderful thing called “Float.”
Free Float Is Important
Some schedule reporting systems only report the Total Float (Slack). Without information on the Free Float, you could have team members interfering with each other's schedule. That costs dollars and teamwork. You also could be losing out on a great tool for negotiating best deals, having meaningful penalty clauses, resource load leveling, coping with urgent unscheduled tasks, control of cash flow, and improving technical results. When you set up a schedule information system, be sure that you are receiving reports on Free Float.
Two Kinds of Float
Suppose a subproject, ABC, includes three sequential tasks: A, B, and C. For reasons of waiting on other tasks prior to B and C, or because the resources are not available on demand, they are scheduled as in Figure 1. Free Float on a task (FF) is the time it can be late in finishing without impacting the start of a following activity. Total Float on a task (TF) is the time it can be late in finishing without impacting the end date of the project (even though some tasks may be rescheduled). Many schedule systems use the word “slack” for what is called Total Float herein.
Negotiate the Best Deal
Normally a planning schedule assumes that a task will be able to begin at its earliest start. However, if we have not yet obtained commitments on tasks, we can perhaps negotiate “best deals” for finishes that include the FF or TF (See Figure 2). For example, in Figures 1 and 2, Task A can be performed any time up to the end of TF (= x + y) if B has not yet been contracted. Ask for two quotes: first, up to the end of the FF; and second, up to the end of the TF. (Of course, you may subtract a bit of time from these just to be on the safe side.) Contractors can benefit from these options by choosing the best workers, choosing an optimum crew, avoiding overtime, working as the materials arrive, choosing the best weather, using it as fill-in between other key jobs, make instead of buy, etc. Give your contractor a chance to use the schedule to make money just as you are hopefully doing.
Within your own organization, “best deals” need not be dollars on your project. The good will of resource managers is important. Give them flexibility for tasks with FF so they will give your critical tasks the attention they need. “Best deals” can also be used in procurement. If the Float is known to the buyer, he may be able to get a better price from a vendor who is allowed to deliver a bit later, but still within the FF, or even TF if the price is right.
Level the Resources for Multiple Projects
Unless the resources are elastic, you can minimize cost and schedule impacts by leveling the load on a team which has an upper limit on the number of employed persons.
In Figure 3, the Float is used to level the load by performing some tasks later, but within the FF or TF. Suppose A, B, and C are attempted by the same resource group, and this results in an overload. Float may facilitate the prevention of this overload.
Negotiate Meaningful Penalty Clauses
Even when there is Float, an incentive for finishing on time is to avoid a penalty for being late. Start the penalty at the end of the FF, because later than this can cost money to negotiate a new start date for a following activity. Then escalate the penalty at the end of the TF, because you may need to negotiate changes in all of the following tasks, and the end date will be in jeopardy. The contractor is sometimes made liable for the consequences of a late finish of a task or subcontract, except for a “force majeure.” In some areas, a bonus must accompany a penalty. This can be handled by making the contract price plus bonus equal to the estimate, and subtracting the bonus after the FF is exceeded (See Figure 4).
Control the Cash Flow
Sometimes the float is many months long. By scheduling completion dates later rather than earlier, but still within the Float, the payments will be later in the project. An advantage of this procedure is a gain in the interest on the money you do not have to pay. This advantage also applies to major capital equipment delivery dates. Use the Float to control the cash flow, but monitor these now nearly critical tasks and equipment deliveries by a number of milestones. Try for an early delivery, but without an early payment. Likewise, schedule the material deliveries close to the need and reschedule them if the project has a serious delay for other reasons.
Monitor FF to Protect Teamwork
When all the tasks on a project are allocated and have commitments, the project team can proceed and complete the job. However, delays will happen (Murphy's Law). Should any task be delayed more than the FF, then it impacts the commitment of another team member, who may be less than enthused about the crisis affecting his or her planned workload. If this happens often, and the end date is in jeopardy, there could be some unproductive finger pointing at the guilty parties. Nobody wins if the whole project is late; therefore, monitor the FF. Do not be misled by having only information on TF, which is often more than the FF. One organization had a terrible lack of teamwork because they only reported the TF on tasks. People thought they had “Float” and acted accordingly, causing disruptions in the work flow.
Avoid Impact Losses
Suppose a task has only one week of FF, but a generous four weeks of TF. If the task is one week late, no problems may be created. But suppose it is two weeks late. That is one week over the FF. Then what? The following activity is affected and loses at least a week. Because of other commitments, tasks may now be three weeks late in completion. Then the following activity is impacted by three weeks and, perhaps when activities are clarified, they and you have lost six weeks. In a large organization the multiple impacts can kill you. One organization attempting an $80 million expansion found that the average cost of a schedule impact was $100,000; therefore, be sure to finish each task before the FF is used up.
Improve on the Technical Results
Why rush a task that has Free Float? Give people a chance to use this time to double check their calculations, drawings, and test results; the extra cost could be trivial in comparison to the improved quality of the work. Many procedures, such as additional life tests, simply take more time but not more manpower.
When a Critical Task is Late, Turn it into an Opportunity
Unexpected delays can make you climb the wall, tear your hair out, or jump out of a window. Hold it! Is there a string of parallel activites which now have extra float? Get in there, analyze the new schedule, and find creative ways to turn that Float to the project's advantage. Money or resources saved now can be used to make up time later.
Exceptions to the Need for Free Float Reporting
There are two cases where knowledge of only TF (or slack) is adequate:
1. The tasks in a sequence are all under one resource manager: If one task is a little late, the manager can assign the impacted person to other useful work and make up the difference later by doubling up on a following task.
2. On construction jobs where the labor pool is large: Generally in a large city, the workmen and subtrades can be turned on and off like a tap. As one trade finishes up, another is called in.
Nevertheless, even in these cases knowledge of FF, as well as TF, will allow the project to be run smarter and smoother.
Keep These Tips Close to Your Chest
This article outlines 7 major uses of float. In seminars, I usually try to elicit 10 uses of float by means of group discussions. Every once in a while we come up with some really unique ones; so keeping looking.
It should be clear now that to reach for excellence in project management, you need to have data on both Free Float and Total Float.
Sydney Love is a consultant in project management and effective time managemant. He is the President of Advanced Professional Development Institute in Los Angeles.
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