Current position of the SSV Corwith Cramer. Click on the vessel to view position history. Use the layer tools, top right, to change the map style or to view data layers. Dates and times use GMT (Greenwich Mean Time).
SEA Currents: SSV Corwith Cramer
November 14, 2017
So Here We Are
12°14.1’N x 060°24.5’W
Description of location
70 nm west of Grenada
300° per ships compass
Weather / Wind/ Sail plan
Easterly trade winds, force 3, occasional squalls, running under the course, top’sl and raffee
“SO, here we are, running before the wind under the topsail and course…” Jesse, sailing intern and current C watch J-WO says to A watch clustered around him on the quarterdeck. His voice comes from a silhouette plastered against a backdrop of stars. “The wind is from the East, force 4. Course ordered is 300 degrees….” he continues. And so began last night’s evening watch.
In some form or another, every turnover from the mate on watch (or now JWO) to the oncoming watch begins this way: “So here we are, sailing under….” But how do we know where here is? Yes, we do have (multiple) GPSs on board but once we left Woods Hole Captain Jason covered the GPS display in the doghouse with a piece of cardboard that says “seek guidance elsewhere!” The electronic chart on the doghouse computer also always has our GPS position, but we haven’t used it to plot our position on the paper chart since the day we left Woods Hole.
So how do we determine where here is? How do we know exactly where we are beside somewhere in the middle of the western Atlantic ocean?
While we could answer that question with one simple look at the electronic chart, SEA Semester curriculum is based on determining and plotting our position with techniques that have been used long before the invention of GPS and computers.
At the top of every hour, when the Doghouse clock bell chimes, someone yells “get the ding!” The watchstander tasked with getting “the ding” rushes over to the port rail on the quarterdeck where the dial for the taffrail log is mounted and reads off the number displayed there. A taffrail log is a weighted metal torpedo-shaped object with a fixed propeller. It is attached to the end of a line that we stream behind the boat. The weighted end spins and works twists into the line which spin a pin in the display mounted on the rail. Kind of like a clock, gears slowly turn the dial or hands of the display, recording how many nautical miles, we have traveled, or what is called the log. We use this information to tell us not only how far we have gone, but also how fast we are traveling through the water in knots (nautical miles/hour).
We also ask the helmsperson (the person who steers) what they have been steering for the past hour. With this information we plot our Dead Reckoning position (or DR position) using our direction traveled and how far we have traveled since the previous plotted position. Every hour we plot a DR position on the chart and the result is usually a pretty good estimation of where we are. But DR can only do so much. DR does not take into account many variables (like current and drift) that could impact the course we made good over the past hour.
So, when we can, we use celestial navigation (using the stars, sun, moon, and planets) to get a more accurate position (or “fix”) plotted on the chart. During the day we can “shoot” the sun to get a celestial fix—“shooting” means using a sextant to measure how high a body (sun, starts, planets) is above the horizon in degrees, minutes, and tenths of minutes. Combining this information with the time the body was shot, we can do calculations that allow us to plot a “line of position.” Our position is the intersection of multiple LOPS. Every morning and evening we can also shoot stars during twilight—a window of time where it is dark enough to see stars and planets but light enough to still see the horizon.
Getting the hang of using a sextant and shooting the sun and stars is tricky and takes a lot of practice. Getting good shots is only the first step—you then have to use the nautical almanac to reduce your sights with a series of calculations and corrections that are pretty confusing at first. This is my fourth trip with SEA and I am only now starting to get more comfortable with the whole process of shooting, reducing, and plotting a sextant sight.
What a lot of work to find out where we are--especially when GPS positions are readily available! Celestial navigation is not just an interesting skill to learn but also one of my favorite parts about sailing with SEA. Being able to use the sun and stars—natural bodies that have existed long before our time—rather than electronics to find our position feels like just another way we are more connected to our surrounding environment out here than on land. Last but not least, knowing where we are is important!
SO, here we are…. running before the wind under the stack of square sails: the course top’sl and raffee, with only one more day of student project presentations left. We have spent the last few days sailing west towards the southeastern Caribbean and bets are in for when we will see land…all signs point to the fact that the end of the trip is drawing near.
Whenever I have a moment to take a step back and reflect on this trip, I can’t help but feel so incredibly grateful for how wonderful it’s been. Thanks to all the students and crew for making it such a good time….after all I firmly believe it’s the people who really make a place. And for me, it’s always the people who always make the boat so worth it.