Creating Hammock Tasks in Microsoft Project 2000

By Bernard Cadwell, Pcubed, Inc. (member, United Kingdom)

A “hammock” is a task that derives its start and finish dates through links pasted from other tasks in the project. In other words, it assumes the duration of the span of the linked tasks, and can expand or contract in duration dependant upon progress. A hammock task 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. For example, given three tasks A, B, and C, task B must start on same date from task A (date A) and task B must finish on same date from task C (date C). For an illustration of this task B, see the example below.

Example – Hammock Task B

The span of time between dates A and C dictate the available time to accomplish task B. As Date A changes, the start date for task B changes as well; If date C moves, task B must finish appropriately. The difference between dates A and C is the duration for task B.

To build the hammock task:

  1. Create or determine three tasks that correspond to A, B, and C in the example above.
  2. Highlight the cell that contains date A (the date that will determine when task B starts).
  3. On the Edit menu, click Copy (Cell).
  4. Highlight the cell that contains the Start date for task B (the hammock task).
  5. On the Edit menu, click Paste Special, and click Paste Link.
  6. Highlight the cell that contains Date C (the date that will determine when task B finishes).
  7. On the Edit menu, click Copy (Cell).
  8. Click the cell that contains the Finish date for task B (the hammock task).
  9. Click Edit, click Paste Special, and click Paste Link.

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.