Could P50 Be Your Biggest Hidden Risk in Project Scheduling?

Offshore wind farm construction schedules can fail for one simple reason: teams rely on P50 without understanding what it hides.

You can build the most realistic model in the world:

🔶 Detailed activity sequence,

🔶 Weather windows & Safe-to-Safe windows,

🔶 Multiple weather datasets

🔶 Vessel interactions

🔶 Port constraints 

…and still give your leadership team the ‘wrong’ answer.

Imagine they ask ➡ “When should we charter the vessel to finish before year‑end?”

You run the simulations, look at the results, and select the P50 duration.

 It feels sensible, not too optimistic, not too conservative.

But here’s the trap: 𝐏50 𝐨𝐧𝐥𝐲 𝐭𝐞𝐥𝐥𝐬 𝐲𝐨𝐮 𝐭𝐡𝐞 𝐦𝐢𝐝𝐝𝐥𝐞 𝐨𝐟 𝐭𝐡𝐞 𝐝𝐢𝐬𝐭𝐫𝐢𝐛𝐮𝐭𝐢𝐨𝐧.

 It tells you nothing about the 𝐬𝐡𝐚𝐩𝐞 of the risk or the impact of considering only the P50. 

When we plot project durations using violin plots, the story becomes clearer. (Swipe through the slides) 

🔹March–July: the distribution is wide around P50 → delays have minimal impact to schedule as range between P10 and P90 is small. 

🔹October–November: the distribution narrows around P50 → delays may shift the outcome towards the P90 case.

▶ In other words:

Your project is likely to finish 𝐞𝐚𝐫𝐥𝐢𝐞𝐫 𝐨𝐫 𝐦𝐮𝐜𝐡 𝐥𝐚𝐭𝐞𝐫 than the P50 suggests.

 And the cost of being late is usually far greater than the benefit of being early.

So perhaps the better question isn’t 

➡ “When should we charter the vessel to finish before year‑end?”

But instead: 

➡  "When should we plan to start operation, and what is the impact of less-favourable weather scenarios?" 

At Scott Marine Consultants, our in‑house marine modelling software Cicada, powered by offshore engineers, is designed to go beyond raw percentile outputs. We combine real‑world context and real-world operational insights helping teams understand not just what the schedule says but where the real risk sits and what this means for your project.