Science Results : Daily Update

Daily Update | Current SEA Research

June 25, 2010

By Giora Proskurowski

If you look at the location map on the home page of this web site, or the data map on this page, you can see that the cruise track is starting to take form. I want to talk a bit about why our route looks the way it does, but have to be careful in this discussion not to jinx our considerable good fortune with the wind and the weather.

As a sailing vessel that likes to sail – motoring is loud and violent compared with the quiet and mostly rhythmic motion under sail – Captain Chris and myself tried to optimize our cruise track to take advantage of the prevailing winds in this region in July. Just as Kara wrote about two days ago – and the reason plastics accumulate in this region – the winds are typically light and variable near the center of the gyre (30°N), with a higher likelihood of easterly winds (from the east) south of 30°N, and a possibility of westerly winds (associated with low pressure systems moving with the jet stream across the U.S.) north of 30°N. After verifying this theoretical prediction of the winds with actual data compiled in a Pilot Chart of the North Atlantic, Chris recommended that we run east along the 32nd parallel (32°N) for as long as possible from Bermuda, and then turn south from there.

If you've read through the daily updates you'll remember that in the first week we motored for a considerable amount of time, but we also got lucky and caught the bottom edge of a couple of low pressure systems and were able to make amazing progress east. As we turned south at around 41°W the winds backed from the south to the east, which would have been unfavorable for an eastbound voyage, but was perfect for sailing south, west, or north – the directions we want to go. Since we turned south several days ago we have had a magnificent sail. In fact, right now we're nicely heeled on a starboard tack, under all the fore-and-after sails (mains'l, main stays'l, fore stays'l, jib, JT, and fisherman) making 8.2 knots – fast for the Cramer.

In about a half hour the crew on evening watch will strike the JT and fish, and double gybe to get into position for a neuston tow on the starboard side. It is fun for everyone when we are doing a lot of science and sailing hard at the same time: the lab is busy setting up for sampling and processing, as well as helping out when the deck crew needs a bunch of bodies to handle all the sail.

Since we turned south, reaching our easternmost point at 40°17'W, we have begun mapping the concentrations of plastics in a large area of the central Atlantic. The best way to make a map is to design a cruise track with evenly spaced passes, much like the way you would mow your lawn.

Because we need to get back to Bermuda by July 14, and we don't have a warp speed setting (although 8.2 knots is pretty much Cramer warp speed), evenly spaced track lines create a cruise track that is much too long. In order to save miles we decided on a sawtooth cruise track, where we get plenty of coverage (albeit uneven), but also gain miles west on every leg. The first leg of our sawtooth is almost complete, with a southern boundary of 26°N and a northern boundary of 30°30'N sometime tomorrow afternoon.

If the winds moderate as we approach 30°N, we may have to motor along the northern edge of the sawtooth. We'll see if the present conditions persist and our nice sail continues, or if I've jinxed the whole operation by detailing our good luck.