Set and Drift
Having just finished the chapter on crossing the gulf stream in Steven Pavlidis’ The Northern Bahamas Cruising Guide, I am reminded of the topic of dealing with currents that we covered in the Fast Track to Cruising course that we took last Christmas.
For the benefit of our Blog readers who are not up to speed on plotting courses, it is hardly ever as simple at steering a straight course from point A to point B. This is especially true when crossing the gulf stream, the world’s largest underwater “river.” If, when leaving Florida to travel to the Bahamas, one was to simply steer a straight course, you would likely find yourself some 10 hours later in the middle of the Atlantic with no land in sight. Because the gulf stream is moving northward at a considerable speed you instead need to take into account how much your boat will be pushed in that direction and thus actually set your course in a more southerly direction. How far south? To determine this involves calculations which factor in your starting point, planned destination, your boat’s speed and the speed of the current. Do we remember how to do all this? Ummmm… sort of. Fortunately the above mentioned book discusses the process, and a quick Google pulls up a bunch of resources too. By the time we get to the point where we are ready to cross we’ll have it all figured out.
The two words in this post’s title, set and drift, “are characteristics of the current or the velocity of water over the ground in which a ship is sailing. Drift is the magnitude of the current (typically measured in knots) and set is the bearing in the direction the current is flowing. Bearing is measured in degrees clockwise from either magnetic or true (geographical) North.” (source: Wikipedia)
The way we were taught to remember which word is which is as follows:
Set has 3 letters = 000 (compass bearings have three digits)
Drift has 5 letters = Speed also has 5 letters
The one thing we have read over and over is that the number one factor in having a pleasant crossing to the Bahamas is weather. Specifically, waiting for the proper “weather window.” Even more specifically, you should never attempt to cross to the Bahamas when the wind has any northerly component (N, NE, NW, etc.). Because the gulf stream travels north any wind opposing it can kick up some very ugly waves. So the trick is to hang out in Florida and wait for a suitable forecast. Although this may take some time, if it will help us to avoid spending hours getting tossed around in vicious seas, we’ll be patient.