Granted, we do not call them Hammocks any longer because P6 introduced a new label: Level of Effort. This is of course an activity type. Why Oracle decided Level of Effort is a better description is rather baffling. During our training classes when we talk about Hammocks most people get the analogy of something that spans from one place to another, just like the hammocks you might see in a backyard. Simply put, a Level of Effort activity measures the distance between a predecessor and a successor. Why is that important?
We typically use a Level of Effort activity to measure the project duration. This is the only accurate means of measuring the project duration if more than one calendar is being used. We assign the Level of Effort activity a calendar that matches the calendar used to specify the project duration. So if the project is supposed to finish within 300 calendar days, we give the Level of Effort activity a 7-day calendar with no holidays.
Another excellent use of this type of Level of Effort activity is to represent overhead and profit on a cost-loaded schedule. Since the Level of Effort activity already mimics the project duration, it gives us a per diem distribution of overhead and profit for the life of the project. This is much easier than trying to add overhead and profit to each activity in the schedule.
In the example below, Activity ID 01 is a Level of Effort activity with two predecessors, and two successors. When there is more than one predecessor, the earliest Start date becomes the Start date of the Level of Effort activity and the latest Finish date becomes the Finish date of the Level of Effort activity. For this to work right, the predecessor relationships must be Start to Start and the successor relationships must be Finish to Finish.
Any activities can be linked with a Level of Effort activity, so this is not always about “effort”. We could link the Start date of the first piping task to the Finish date of the last piping task and this would give us the overall duration of piping work. But if we tie the Level of Effort activity to something other than the first and last piping tasks we are not describing the overall timeframe for piping correctly. A WBS Summary activity is another option (which we will discuss later) if the only goal is to show a summary bar. Keep in mind, the duration of a WBS Summary activity may be incorrect unless all the activities it summarizes share the same calendar.