Dependent task - "Hammock task"
A colleague of mine presented me with a problem in a MS Project. He wanted to create a "Project management" task that lasts as long as the project last, so he could point out that the whole project process is being supervised by PM staff. In this case the perfect solution is a "hammock" task.
A "hammock" task is a task that is dependent on external dates for both its start and finish dates and, ultimately, its duration. The name, hammock task, is derived from the way a hammock's shape is determined by the distance between the points to which it is attached. As scheduled dates in other tasks change, the duration and start and/or finish dates of the hammock task change as well. In other words, given three tasks A, B, and C, task B must start on some date from task A (date A) and task B must finish on some date from task C (date C).
But enough with the theory, let's get down to practice:
Setting a "hammock" task in MS Project:
- Create a new task
- Click on the finish date of the task that will drive the finish date of the newly created "hammock" task
- Copy it (Ctrl+C, Edit->Copy Cell)
- Go to the finish date of "hammock" task and do the following: Edit->Paste Special and select Link
- Repeat the steps 2-4 for the start date.
Notes and cautions:
- Do not specify a predecessor for a hammock task. Only Paste Linked dates will determine start and finish. You may specify predecessors for the tasks from which dates are paste linked into the hammock task.
- A negative duration (finish date is before start) is not allowed. Depending on the source of the dates, the hammock task may turn into a milestone (zero duration) or erroneously calculate duration before the finish date or after the start date.
- An OLE update is different from a calculation. You may not see expected changes in the hammock task after calculating project. From the Edit menu, click Links to edit/update OLE links (Paste Links). Alternatively, press the F9 function key twice.
- Because the hammock task relies on other tasks for start/finish information, anything that affects those other tasks (resource leveling, constraints) will ultimately affect the hammock tasks dates.
- If the hammock task is a child to a summary task, it may inherit predecessor behavior from the summary task that may affect its duration and/or start and finish dates or create a circular relationship