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River Science: Water Depth

When traveling through uncharted waters, one of the most basic questions a ship's crew needs to be able to answer is also one of the most important: How deep is the water? In fact, as Juet's journal entries show, Captain Hudson and his crew repeatedly faced the danger of running aground while exploring the river that would later bear his name.

When in doubt, we take soundings (measure the water's depth) with the same tool Hudson's crew would have used: a lead line (or sounding line). Flags attached to the lead line mark depth in 6-foot increments (fathoms). The Half Moon has a draft of 8-1/2 feet (extending that far underwater), so it needs at least a fathom and a half of water to stay clear of the bottom.

Monitoring water depth is just as important for us on board the Replica Ship Half Moon. Of course, in 21st century the Connecticut River has been throughly charted and (unlike Captain Hudson) we have experience navigating this river, but that doesn't mean there are no uncharted waters for us to explore. On this voyage, we moored at the Goodspeed Opera House dock for the first time. The evening before we arrived, we sent a scouting party to sound the dock with a lead line, and discovered that the water was just deep enough for the ship's draft.

In addition, once the ship arrived the next day, we temporarily installed a depth finder to mark the tidal changes until our arrival, less out of scientific curiosity and more out of practical necessity! We're glad to say, however, that in the end the Goodspeed Opera House dock was indeed deep enough to safely house our ship.

In Hudson's day, crews would even use their lead lines to take samples of the river bottom. They could fill a small hollow on the bottom of the line's lead weight with tallow or grease, then see what stuck to this goo when they retrieved the line. Silt or sand made for a fine anchorage, but clean tallow warned of rocks lurking below, making anchorage dangerous if not impossible.

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