So you want to send a message in a bottle, and you’re hoping that someone, somewhere, will find your missive and still be able to read what you’ve written.There’s a strategy involved, and while some of it’s obvious (choose a dark bottle), other aspects require a little more forethought.

Inspired by the recent discovery of a postcard from 1913 bobbing in the Baltic Sea, an MIT expert consulted by Popular Mechanics breaks it down:

“It depends entirely on where it’s thrown into the ocean,” says Thomas Peacock, professor of mechanical engineering and fluid dynamics at MIT. “Some parts of the ocean have very steady, predictable currents, but others tend to meander a bit.”

Fortunately, this 101-year-old bottle bobbed into the Baltic Sea, a far more predictable body of water. The Baltic is essentially a closed basin bounded by nations including Sweden, Finland, and Estonia, with water that flows in a neat, counterclockwise pattern at a relaxed rate of 1 cm per second. “It looks like it would take a bottle about three years to circulate around the Baltic,” Peacock says. “So we’re basically saying that, over 100 years, it would have made something like 30 trips.”

Popular Mechanics also spoke with David Holland, professor of mathematics and oceanography at New York University’s Courant Institute of Mathematical Sciences, who advises “rolling the paper inward” and using the darkest-possible bottle to avoid fading the message in the sun. Oh, and avoid any spots that seem overpopulated with barnacles:

Holland says that the sea is not only full of chaotic currents, but also teeming with marine life. “When we put any equipment in the ocean, life grows on it quite voraciously,” he says. “In the case of a beer bottle, whether life makes it sink or float would depend on whether the life form is buoyant or not.”

Image via Shutterstock