Modelling Expected Breakdown

In yesterday’s entry about modelling breakdown, I introduced the idea that from next week, Mermaid enables the modelling and analysis of technical breakdown. The new feature that we’re releasing is called “Occasional Tasks”.

An Occasional task or group is one that only happens for certain repeats of its parent group. So, take this very simple task diagram for a survey job to start with:

We’ve got 60 survey lines to complete, and each one takes an hour and a half. Our “Survey One Line” group is repeated 60 times to show this. Mermaid can analyse this operation, and produce a set of weathered results.

But, what if your survey equipment isn’t well suited to the conditions you are operating in, and it fails 10% of the time? In that situation, you need to head back to port and fix the equipment. So we add a new task, “Repair Survey Spread” and place it in-line with the existing run. This needs to be done back in the port we mobilised out of, so we can give it that location. Remember, Mermaid automatically inserts transits so that our vessel gets to where it needs to be.

Next we need to ensure that it doesn’t happen for every survey line, so we click the new option that we’ve got in the “Repetition” section of our task details window:


Here, we can specify a number of items:

  • When the task first occurs: We don’t want this task happening the first time out – equipment checks will have been done during mobilisation, we wouldn’t expect it to fail straight away.
  • How often the task occurs
  • The maximum number of times the task occurs: This isn’t so useful for our present application.

Now, looking at the task diagram, we see that the Occasional task is marked out with dashed lines:

And in the Gantt Chart we can see that for the first few repeats, the repair task doesn’t occur:

But as you get into later repeats, the task appears. Notice that the transit back to port is automatically inserted, and has a significant impact on the schedule.

And this demonstrates nicely the way in which we can model breakdown in a long job where we expect to see breakdown on a regular basis. Maintenance job, crew changes, etc. can also all be scheduled in this manner.

Mermaid will weather the repair task, and transits to/from port in just the same way as if the task were a normal task; so weather-limited repair tasks will only be carried out where they are wanted. If a repair task can be carried out offshore, then you can simply leave the location at the Group’s location and it will happen there.

Furthermore, if a repair is more sophisticated than a simple task, you can make a whole group Occasional:

In summary, you can use Mermaid to model repair strategies in as much detail as you wish, allowing you to get real confidence that your long-term projects will complete when you expect them to, and no later.