Odysseas Froilan, a marine engineer, lowered a GoPro camera over the side of the hull on a line while a cruise liner was anchored in water that seemed from the deck to be any other picture-perfect blue Caribbean bay somewhere in the Bahamas. A few meters below the waterline, the footage did not show what most individuals standing at that barrier would have anticipated. Fish gathering close to the anchor chains, remoras clinging to the hull plating, pike-like shapes moving through the structural shadows, and at nite, sharks emerging from the shadows outside the ship’s frame, circling, passing, and swiftly vanishing back into the water that the footage made appear extremely dark and deep.
The video went viral because it revealed something that people were unaware they were standing just over. Cruises are taken by millions of people. They see blue sea and possibly a far-off shoreline as they stand at the railing and gaze out at the ocean. Looking up at a hull that extends farther than you might anticipate and fades into shadow at an angle that makes the scale difficult to comprehend, the camera depicted how the ocean seems from the opposite direction.
The anchor system alone, which is recognizable as a mechanical fixture from deck level, takes on a distinct appearance when it vanishes into the water below. The response on the internet was predictable in the same way that responses to truly frightening things usually are: a combination of fascination and a particular kind of discomfort that has its own name. The fear of massive submerged man-made items, known as submechanophobia, was more common than most people believed until the video gave it a tangible trigger.
In fact, those who research marine biology are not as surprised by the footage as the broader audience was. Fish are drawn to large vessels. The barnacled plate and anchor chains provide attachment surfaces for smaller species, the hull adds structural complexity and shade to an otherwise featureless water column, and the subsequent food chain—small fish attracting larger predators—is a predictable outcome. Sharks are known to patrol the shadow zones surrounding anything big enough to offer cover, and remoras are known to cling to huge moving objects. For a marine biologist, none of this seemed noteworthy. The video was noteworthy because it revealed to non-specialists what they had been thinking about but were unable to visualize.
The footage relates to a safety aspect that cruise lines and maritime safety organizations take very seriously when it comes to the wake and thruster dynamics. The water immediately surrounding the hull of a cruise ship in operation is not calm. Strong, directed water jets are produced by thrusters used for port maneuvering. When the main propellers are operating, they create a screw wash, which is a high-velocity helical current that extends far behind the ship and causes turbulence at a scale that makes the near stern zone actually dangerous.
The churning, aerated water reduces buoyancy, the turbulence prevents directional swimming, and the visibility for rescue teams looking into white water from above is practically zero, so a person entering active propeller wash has very little chance of being recovered. This is not primarily due to the propeller blades themselves.
The propeller wake environment plays a major role in the poor survival statistics profile of man overboard occurrences at sea. The size of the ship’s hull and the depth of the water apparent in the footage made the hazard more understandable to general audiences than any safety briefing could, even if Froilan’s footage did not clearly document this—the ship was at anchor, not at speed. A different kind of comprehension results from seeing the depth of that anchor system and the amount of structural mass beneath the waterline than just reading about it.
