the British steamer "Rumney" crashed into the French ship "Frigorifique."

Seeing their ship filling with water,

the French crew climbed aboard the "Rumney."

But as they sailed towards the nearest port,

a silent form suddenly emerged from the fog:

the abandoned "Frigorifique."

It was too late to turn,

and the impact was enough to sink the "Rumney."

As the sailors scrambled into the lifeboats,

the empty "Frigorifique" sailed back into the fog,

having seemingly taken its revenge.

In reality, the French sailors had left the engines running,

and the "Frigorifique" sailed in a circle

before striking the "Rumney" and finally sinking.

But its story became one of the many tales of ghost ships,

unmanned vessels that apparently sail themselves.

And although they've influenced works like "Dracula"

and "Pirates of the Caribbean,"

crewless ships aren't the product of ghostly spirits,

just physics at work.

One of the most famous ghost ships was the "Mary Celeste",

found sailing the Atlantic in 1872 with no one aboard,

water in its hold,

and lifeboats missing.

The discovery of its intact cargo and a captain's log that ended abruptly

led to wild rumors and speculation.

But the real culprits were two scientific phenomena:

buoyancy

and fluid dynamics.

Here's how buoyancy works.

An object placed in a liquid displaces a certain volume of fluid.

The liquid in turn exerts an upward buoyant force

equal to the weight of the fluid that's been displaced.

This phenomenon is called Archimedes's Principle.

Objects that are less dense than water,

such as balsa wood,

icebergs,

and inflatable rafts always float.

That's because the upward buoyant force

is always stronger than the downward force of gravity.

But for objects or ships to float when they're made of materials, like steel,

that are denser than water,

they must displace a volume of water larger than their weight.

Normally, the water filling a ship's hull would increase its weight and cause it to sink -

just what the "Mary Celeste's" crew feared when they abandoned ship.

But the sailors didn't account for fluid dynamics.

The water stopped flowing at the point of equilibrium,

when it reached the same level as the hole.

As it turned out, the weight of the water wasn't enough to sink the ship

and the "Mary Celeste" was found a few days later

while the unfortunate crew never made it to shore.

Far stranger is the tale of "A. Ernest Mills,"

a schooner transporting salt,

whose crew watched it sink to the sea floor following a collision.

Yet four days later, it was spotted floating on the surface.

The key to the mystery lay in the ship's heavy cargo of salt.

The added weight of the water in the hull made the vessel sink,

but as the salt dissolved in the water,

the weight decreased enough

that the force of gravity became less than the buoyant force

and the ship floated back to the surface.

But how do we explain the most enduring aspect of ghost ship legends:

multiple sightings of the same ships hundreds of miles and several years apart?

The answer lies in ocean currents,

which are like invisible rivers flowing through the ocean.

Factors, like temperature,

salinity,

wind,

gravity,

and the Coriolis effect from the Earth's rotation

create a complex system of water movement.

That applies both at the ocean's surface and deep below.

Sailors have always known about currents,

but their patterns weren't well known until recently.

In fact, tracking abandoned ships was how scientists determined the shape

and speed of the Atlantic Gyre,

the Gulf Stream,

and related currents in the first place.

Beginning in 1883, the U.S. Hydrographic Office

began collecting monthly data that included navigation hazards,

like derelict ships, whose locations were reported by passing vessels.

So abandoned ships may not be moved by ghost crews or supernatural curses,

but they are a real and fascinating phenomenon

born through the ocean

and kept afloat by powerful, invisible, scientifically studied forces.