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River Science: Current Speed

Current speed is a major factor for any waterborne vessel. When we sail with the current, the water travels with us, speeding us along. When we move against the current, the oncoming water pushes against us, slowing us down. In addition, the Hudson River is an estuary and is thus affected by ebb and flood tides, causing the river's current to slow and even reverse itself several times a day. Keeping track of the current is vital for ships looking to make good time on the river. This was even more true in the 17th century, when attempting to sail against the current's strength could easily prove futile.

On this voyage, the research team of Grace and Abigail measured current speed and direction for their presentation project.

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 toss a biodegradable wood chip (or a banana peel, as the case may be) 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.

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