Cruising Tips: Understanding Set and Drift Tactics

Publish date:
Social count:
Attempting to sail the 114 degree course

Attempting to sail the 114 degree course to Gun Cay, the boat must head up into the current to avoid being set north

An understanding of the effects of set and drift is vital for coastal sailors; it can make the difference between an enjoyable passage or a struggle to reach your destination against a foul current.

As an example, let’s plan a Gulf Stream crossing from Miami to Gun Cay, Bahamas. You know it is safest not to cross the stream in any wind with a northerly component, so you are excited to hear that south-southeast winds will persist for two days at a moderate 10 to 15 knots. Your course to Gun Cay is 114 degrees magnetic, making you confident that you can sail in the predicted 160-degree wind. With no seas, in a boat that points well, you may be correct—were it not for the Gulf Stream.

The stream averages 1.5 knots where it intersects the route from Miami to Gun Cay. Depending on the speed of your boat, this may have a significant impact on your course, since the current runs almost perpendicular to your route. In a powerboat the effect of the Gulf Stream is negligible, but in a sailboat, especially one wishing to sail rather than motor, this current can make what at first appears to be a pleasant sail into an impractical and unpleasant experience.

Correcting the course to allow for set

Correcting the course to allow for set, the boat must steer 132 degrees rather than the 114 degrees rhumb line

Set and drift are two terms used to describe the effect currents have on your boat. Set is the direction in which the current is flowing—in this case, 18 degrees. Drift is the speed of the current. You need to take both of these into account when taking advantage of a weather window to cross any strong current.

Some sailors mistakenly believe that because they have a GPS to tell them what course to steer, they do not need to understand the effects of a current such as the Gulf Stream. This is simply not true. While your GPS will indeed display the straight line between you and your destination, it will not predict the effects of set and drift, which can change a favorable wind direction into a headwind.

Never forget that a GPS is reactive, telling you how to correct your heading to stay on course. This means that at the beginning and end of your passage, you will be sailing the predicted heading. However, in the middle of the stream, where the drift is strongest, you will have to point further and further into the current in order to remain on your rhumb line. Such a drastic change in your heading also brings the wind further forward so that you will be beating into it and, eventually, motorsailing. Not only does this eliminate the sailing option, it can also make for a less pleasant crossing.

By being able to predict the current’s effect, you can choose a weather window that allows for an easy Gulf Stream crossing under sail. You can use set and drift to plot the course you should steer to arrive at your destination on a more consistent heading, spreading out the effects of the stream across the entire passage, rather than simply reacting to it when it is at its greatest.

Wait for a southerly wind unless you want to motor all the way

It is now apparent that it will not be possible to sail to Gun Cay with this wind direction. Wait for a southerly wind unless you want to motor all the way

1. Find the distance to your destination in nautical miles.

2. Divide this distance by your average speed in knots. (Using your average speed is important. We all like to think our boats sail faster than they really do, so it is important that you be honest here.) This gives you the length of time of your passage.

3. Multiply this time by the average speed (drift) of the current. (The Gulf Stream averages 1.5 knots across this Miami-to-Gun Cay route.) This gives you the number of nautical miles in the direction of the current that you would be swept if you did not correct at all.

4. From your destination, plot the set of the current.

5. From your destination, measure the distance you found in Step 3 along the line you plotted in Step 4, in the opposite direction of the current. This gives you a point to use to find your course to steer.

6. Measure the bearing from your departure point to the point you found in Step 5. This is your course to steer.

By following this method, the bow of the boat will be pointing in the heading you found in Step 6, but the current will sweep you along the line that takes you to your original destination.

Let’s look at the numbers for the Miami to Gun Cay example.

1. Distance: Miami to Gun Cay is 47 nm.

2. 47 divided by our average boat speed of 4.5 k equals 10.44 hours.

3. 10.44 hours times 1.5 knots of current equals 15.67 nm.

4. Plot the current at 18 degrees through Gun Cay.

5. From Gun Cay, measure 15.67 nm in the direction opposite the current: 198 degrees.

6. Determine the course from Miami to this new point. The course to steer is 132 degrees, though the bearing to Gun Cay is actually 114 degrees.

With the wind coming from 160 degrees, it now becomes apparent that it is impossible to sail to Gun Cay. You will have to wait for a more southerly wind in order to sail across the Gulf Stream between these two points. The other option is to depart Florida at a point farther south. But be sure to calculate the set and drift and determine your new course to steer, which will differ for every location. 

Connie McBride and her husband, Dave, are meandering around the tropics on their Creekmore 34 Eurisko

December 2016



The ICW North Bound Migration Begins

As the northbound migration begins, we are getting some early reports on conditions along the ICW. The overall impression this spring is that after the damages caused by the hurricanes, the winter storms have apparently not made too many additional changes. There is even some more


Charter: Historic Croatia

Heaps of history—that’s not usually what comes to mind when you plan a sailing charter, but if you like a bit of culture mixed with your cruising, Croatia is the place to go. Caught between two worlds, (the whitewashed laid back vibe of the Mediterranean and the brash demeanor of more


Gear: Pan-Pan man-overboard Locator

There He Goes!The Pan-Pan man-overboard locator won a Pittman award for 2017 as a great idea, and now it is in production as the Weems & Plath CrewWatcher. It’s a two-part system that employs a smartphone app to locate a small personal beacon that triggers automatically should more


SAIL 2018: Reader's Photographs

Are you out there sailing, cruising and living the sailing life? If so, we’d love to see it. Send your sailing photos to sailmail@sailmagazine.comAnd don’t forget to sign up for our free eNewsletter.Check back for updates!This was taken from half way across the 26 mile crossing more

Landing Page Lead

The Volvo Returns to the Southern Ocean

Since the Volvo Ocean Race’s inception, the Southern Ocean has made it what it is. And no part of the race says “Southern Ocean” like Leg 7 from Auckland, New Zealand, to Itajaí, Brazil. The 7,600-mile leg, which starts this Sunday, is not only the longest of the event, but far more


SAIL's Tip of the Week

Presented by Vetus-Maxwell.Got a tip? Send it to sailmail@sailmagazine.comTeak deck paradise  I had a call recently from the man who replaced the deck on my Mason 44 five years ago. He was worried about the way people are wrecking their teak decks trying to get the green off. more


Gear: ATN Multi Awning

THROW SOME SHADEAmong the many virtues of cruising cats is the large expanse of netting between their bows, which is the ideal place to hang out with a cold one after a hard day’s sailing and let the breeze blow your worries away. Only trouble is it can get a bit hot up there more