Crossing the Stream
We are, of course, talking about the Gulf Stream - that stream which is part of a world-wide system of ocean currents. Our discourse here is about the various methods of crossing the Gulf Stream - specifically about crossing the Gulf Stream from Florida to the Bahamas.
There are two methods from which to choose: Rhumb line and Rum line.
The definition of Rhumb line - n. The path of a ship that maintains a fixed compass direction, shown on a map as a line crossing all meridians at the same angle.
There are two methods from which to choose: Rhumb line and Rum line.
The definition of Rhumb line - n. The path of a ship that maintains a fixed compass direction, shown on a map as a line crossing all meridians at the same angle.
The definition of Rum line, at least ours, is the path that gets you there most quickly - so you're sitting at the bar, waiting for those who chose the shortest distance rather than the shortest time.
First, let's muddle through a few facts about the Gulf Stream which concern us. If you are not one who believes in facts, or if they frighten you, you can skip this part.
First, let's muddle through a few facts about the Gulf Stream which concern us. If you are not one who believes in facts, or if they frighten you, you can skip this part.
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The Gulf Stream meanders. It is like a river which has no banks. We have seen it as close as a quarter mile from the Florida Coast in spots. Other times you will not encounter it until you are many miles out. |
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The Speed of the Gulf Stream varies. Obviously, in areas where it happens to be narrower it is faster than in wider areas. The speed is up to 2 meters per second. This is equal to 3.88768898488121 knots. (I told my wife I needed a conversion calculator - and want her to know I use it.) You can read a very scientific sounding page on this at: http://kingfish.coastal.edu/gulfstream/p2a.htm. But be warned there are very dangerous words such as 'isopycnals.' I sprained my tongue and injured three brain cells, one of them beyond repair, on that word alone. |
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The Temperature of the Gulf Stream is usually above 80° F. If you have a water temperature sensor and gauge on your vessel, you'll know when you encounter the stream. Check your coastal water temperature when you leave. If, for instance, it is 75° when you leave and it suddenly rises to 78° or 79°, you have entered the stream. It will probably continue to climb until you reach the center of the stream at about 85° F. |
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There are Eddies along the Gulf Stream. These are quite large when you get further north, but we have found smaller ones when traveling along the coast. They can fool you into thinking that you're in the Stream itself - or, if you're on the wrong side of them suddenly carry you off in a direction you didn't anticipate. |
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Wind and Weather have a profound effect on the Gulf Stream. If there is any northerly component to the prevailing wind you will want to wait for your crossing. Wind out of the north against a current which is heading north makes for big, uncomfortable sea conditions. |
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The Gulf Stream is about 30 miles wide off of the coast of Florida - it varies. The distances from points in Florida to points in the Bahamas, as the crow flies, are roughly 45 to 55 miles. So you will be in the stream about 1/2 to 2/3 of the distance. |
For those of you who have money to spend on excellent current charts of what the stream is doing (this may be of great benefit to racer sailors) check this site: Jenifer Clark's Gulfstream
There are two ways to cross the stream, as we indicated above: Rhumb line and Rum line. Look at the pictures below.
Not to be used for navigational purposes
On your left is Florida. On the right, Kokomo, your destination Island in the Bahamas - famed in song. The dotted line is your Rhumb line. In case you have trouble following this dissertation, the dark blue is the Gulf Stream, the light blue is the part you have to cross that's not moving. (Green is land - I'm pretty sure you knew that - if not, I don't know what to tell you.)
Not to be used for navigational purposes
Not to scale - unless your boat is really, really big.
If you insist on traveling the Rhumb line
, your boat will be crabbing along as shown above. Let's assume, for argument's sake, that the total Rhumb line is 60 miles; that your boat can make headway at 6 knots; that the stream is 30 miles wide. We will discount the fact that you are traversing the Stream at an angle, thus increasing your time in the stream. Your time not in the stream is 5 hours. (60 miles total - 30 miles stream = 30 miles; 30 miles at 6 knots = 5 hours)Inside the stream, because you are being set by the current, for every mile you travel toward your destination, you will be set a mile. So your headway will be approximately 3 knots for 30 miles. That's 10 hours you've spent in the stream and five hours out of the stream for a total of 15 hours.
If you travel the Rum line
, you may maintain the same course until you hit the stream, then you set course at a 90° angle to the stream's direction toward the opposite side. You allow the stream to set you. Since it's 30 miles across the stream it takes you, at 6 knots, 5 hours to get across it. But you've been set 15 miles (3 knots current for 5 hours). Traveling directly toward your destination at 6 knots it takes 2½ hours to make up that 15 miles. Add to that the roughly 5 hours to traverse the waters outside the stream and you have a total of 12½ hours. Yes, I know that actually it is even less than that because this calculation assumes right angles to make up the set instead of the diagonal. But I've forgotten most of my high school geometry.So Rum line beats Rhumb line by about 2½ hours.
And depending on your location of departure, you might work it out that you took care of the set a day or more before by choosing your departure location further south and so, if you calculate correctly, make your crossing in even less time. There are many other factors which enter into this calculation - variables mentioned above such as the location, width and speed of the Stream on the day of your crossing; as well as wind direction and speed which may help or hinder you if you are motor sailing. We at the Frugal Mariner are of the opinion that if you have to alter course to take advantage of the wind while crossing the stream, it is most likely to your advantage to drop your sails and just motor across.Above we spoke of a constant speed of the Gulf Stream of 3 knots. Not only does this vary, but it varies from the edges to the center. At the edge it may be only 1 or 1½ knots while at the center you may encounter 4 or 5 knots. If it were to get up to 6 knots, that is, the same as your boat speed, and you still insisted on a rhumb line, you will never get out of it. Until you run out of fuel - or wind.
WARNINGS:
Always, ALWAYS have a deep respect for the weather and a healthy skepticism for the prognostications of the so-called weather experts. Check with several sources. Do NOT rely on others - especially other cruisers. Even if they sound authoritative on the cruisers' net, double check your own sources. NO disrespect for the good they have done, but NOAA's weather forecasts have gotten us in trouble on more than one occasion - caused us to have to call in our one and only Mayday many years ago. (In NOAA's soothing, voice - "waves two to three feet, winds 10 to 15." Outside the boat - breaking waves 10 to 12 feet, winds 50k+ in a 21 foot sailboat and the rudder broke off - but that's another story. Needless to say we lived , and learned a lot!)
FILE a FLOAT PLAN. You are traveling by yourself, well out of sight of land. All kinds of things can happen. Whether you've crossed the stream 100 times or this is your first, File a Float Plan! Check our Float Plan Page.
Time Your Arrival to the Bahamas so that the sun is high. You'll be able to see the shoals and sand bars. These shift faster than charts can keep up.
Entering the Bahamas with a pet? You need the right papers. Check out our Cruising with a Dog or Cruising with a Cat Page.
Make sure you carry enough cash for entry to the Bahamas. They want cash - not check or charge when you clear in.
Check out: Bahamas - Formalities (the emphasis on that word is probably on the FORM part.)
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Notice: While we make every effort to ensure that the information provided on this website is accurate, we can not be held responsible for any mishaps which may occur as a result of your using information found in this website without verification through other, more authoritative sources such as the U.S. Coast Guard. |
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