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Measuring the current is trickier than it looks. Our crew members learn that waves rippling across the water's surface are actually caused by the wind (and, with practice, can even be used to estimate wind speed) -- but those ripples don't tell us anything about the current's speed or direction.

Waves may not tell us about the current, but debris floating in the water can. To measure the current, students would toss a biodegradable wood chip into the water, then time how long the chip takes to float down the length of the weather deck. Some quick calculations are then needed to determine in what direction, and how strongly, the the water is pushing us.

However, the students' own findings gradually determined that the wood chips were prone to error. Although they had very little surface area, they were so lightweight that they could still be affected by the wind. Starting with this voyage, we have started experimenting with using a tethered "float bottle" as well, which has been weighted to retain just enough buoyancy to remain on the surface. This bottle is retrieved after each speed test.