As a result, former Stanford researcher, Frank Lossaso-Petterson, who helped build the university's fluid sim engine that has assisted ILM, was hired on staff to create the Maelstrom. "We needed to simulate a lot more water and for the Maelstrom sequence there were a lot more shots that had to be done," explains the fluid sim expert. "It became clear early on that the resolution needed was above and beyond anything we or anyone else had done before. With respect to R&D, we needed a way of getting all that visual detail on the surface that director Gore [Verbinski] wanted and at the same time be able to run in a short enough time to get a few iterations. The first couple of simulations that we ran in the traditional, Poseidon way, in parallel and on the newest machines, revealed that we would've needed another 10x the amount of time to attain the required resolution. So it became clear that we needed some technological changes.

"The Stanford engine allows us to run a basic photorealistic simulation. However, it's been extended at ILM to allow for greater control for art direction and rendering. So I've developed a lot of tools to make that work on top of the basic engine, as well as other tools in order to make the engine more accessible to a lot more people. One of the new tools focused on manipulating data, so that if the director wants it to go a little faster or spin faster in certain areas, we could handle this in a quick turnaround. That led to us having to deal with other challenges, such as manipulating the data of water underneath a ship that is interacting with this water. So we developed technology where we could add in the ship interaction after running the general overall water motion, which had a lot of advantages. Not only could we manipulate the overall water motion and then add the weight afterwards but we could also run a single simulation for half the shots and then another simulation for the rest of the shots. We could also run individual simulations for highly detailed shots with greater resolution.

"On the rendering side, one thing that was a little strange was that because the Maelstrom was bowl shaped, you end up looking at the water from a shallow angle up close or from an over the top view farther away. The rendering challenge was that we would have to deal with this level of detail change for water that is just a couple of feet from the camera to water that is several hundred yards away from the camera. You obviously have to handle the water differently if most of it is obscured by other waves when you see everything from a top down view.

ILM took on 750 of the most difficult shots, including work on Captain Jack Sparrow's bizarre hallucination as the wall encrusted member of The Flying Dutchman. The hard part was getting all the texture and doing all the paint work.

"Distances were in the thousands of feet. Just a rough calculation that we came up with for the amount of water that we were simulating for this was the 15 billion gallon mark. And if you need resolution down to just a few feet per cell, or even less than that, you can't just brute force that computationally, even with all of the parallelism that we have and state-of-the-art computers. This is where the ability to supplement simulation with wake and detailed sims comes in handy.

"One technique that we used was... to simulate the Maelstrom as though it were flat and basically perturb gravity... because the surface is what matters. Instead of sloping down, the gravity was really pointing inward. And then part of the post process tools that we have would be to deform the surface into the shape that we wanted. All the art direction is being established while we run these shots. All these advancements made feasible what otherwise would've taken 40-45 weeks to render. And with parallelism across 40 processors, you take that down to a few weeks. And then running the simulation in a flat domain, as I've just described, brought that down to a few days."

As Knoll explains, the ability to composite two simulations at different resolutions and then apply deformations and overriding animations, enabled Verbinski to achieve important visual clarity. "It was important to Gore to really read that the water spins faster and faster as you go farther down into Maelstrom," Knoll adds. "The story points required you to see certain moments clearly: When The Flying Dutchman and The Black Pearl are on opposite sides of Maelstrom and The Flying Dutchman cuts down lower latitude into the faster water, it takes this faster track to close the gap and pull in right behind The Black Pearl. But when we actually ran a fluid simulation with all the correct mathematical calculations, it may have been physically correct but it wasn't dramatically correct. Because when you framed up a shot, Gore didn't think the water lower in frame was moving sufficiently faster than the water at the top of the frame to convey his story points."

Another unexpected moment occurred during the Maelstrom sequence when there wasn't a sufficient number of Flying Dutchman crew to fight. At a certain point in the sequence, the two ships connect and their masts become entangled, and you have crusties fighting on both ships. "Having built 17 members of Davy's crew for Pirates 2, we didn't think we'd need additional characters for Pirates 3," Knoll continues. "But as we began laying out the choreography of Maelstrom and figuring out who's where and when, we came up short when we split up the Dutchman crew. We didn't realize until we began shooting this in December. We added around 10 more Dutchmen. And they are very labor intensive to build and paint and set up."