Details on Crossing to Bimini

February 5, 2016 by Jesse K on s/v Smitty 9 Comments

Two key factors come into play when crossing the Gulf Stream: the weather and the set and drift.

Weather

The weather is key because any winds from the north will give you wind against current that will result in some nasty conditions in the stream. The prevailing winds in the Miami to Bimini, Bahamas area is typically south east. The south component is good but the east component can stir things up and build up some seas, but typically not as bad as north winds.  But you are traveling in a general east direction so southeast winds typically mean no sailing. If you wait for a perfect window you could get south or west winds that would allow you to sail. We had already waited for a week for anything that would be considered good conditions for crossing the stream.  We weren’t about to wait even longer for a weather window that would give reasonable seas and sailable wind.

Instead we were looking for what is referred to as a trawler crossing.  We wanted the most benign conditions.  We were ok being a motor boat a few more times after our trip down the ICW but we really are itching to sail again. As a sailor you watch the weather more than most.  A sailor planning a passage watches the weather with an obsession that is more a kin to a drug addition.  I can tell you what time each day my four favorite sources update their information. Chris Parker, the weather guru, does a free broadcast at 06:30 EST on the Bahamas on the SSB radio and on a webcast. Our day will typically start by listening to Chris.  While he is covering other areas that we are not currently concerned about, I jump on Windfinder, NOAA Marine and Passage Weather.  If there is time I will also check the Weather Channel, Weather Underground and Accuweather.  We are looking for the combination of winds from a direction other than the north and speeds as low as possible but absolutely below 20 knots.  Even 15 knots can stir things up good. 

These various forecasts seldom agree.  A couple may have the direction the same or the speed but very rarely both.  Eventually you will get a feel for the forecast vs. reality enough to make a decision on a window to go.

Of course this January had a very unstable and difficult to predict weather pattern. We had already gone through several severe weather events in Florida including tornado warnings where tornadoes did touch down in the area of the boat. Some were blaming the strong El Nino. Others just think January is one of those months where weather patterns are less consistent. Regardless, the results were potential weather windows that would appear to be there and then disappear the day before departure. So we waited.

Set and Drift

The set and drift are important to help you determine you departure location and the course you will steer once you do leave. The set is the direction you are pushed off your course.  The drift is the speed you are pushed off your course. The Gulf Stream runs anywhere from less that a knot to 4 knots to the north. Most people use a north set and a drift of 2 knots to calculate their course for a Gulf Stream crossing.  Passage Weather is a good source to look at the actual set and drift of the stream.  But using 2 knots north will get you in the general direction most of the time.  One thing to keep in mind is that the current fluctuates throughout the Gulf Stream.  So you might see less than a knot when you first enter the stream about a mile or so off of the Florida coast, or you might see 4 knots running at the peak of the stream. You can use this to your advantage.

You can calculate a course to steer that accounts for set and drift using a course board.  This is a skill we both have thanks to the navigation portion of our captain’s license course.  Most boaters do this using a GPS and just keep adjusting their steering to keep them headed towards their target.

With slower moving vessels like sailboats you don’t want to simply keep aiming south to keep your boat moving in the general direction of your planned port of entry. This would work with boats that can travel over 10-15 knots.  But in a sailboat the result would be that you would eventually aim almost straight into the current, slowing you down to a snail’s pace and keeping you in the stream longer. As you turn more into the stream your velocity made good to your planned point of entry drops to 1-2 knots. This can result in a crossing that takes you upwards of 24 hours to complete.

Instead, once you know the set and drift you can start to plot your route that will get you across the Stream as quick as possible without pushing you north of your planned point of entry. 

It’s approximately 44 nautical miles from Florida to the Bahamas. We use an average boat speed of 5 knots when planning our routes.  So at 5 knots it would take us approximately 8 hours and 45 minutes to cross to the Bahamas. During that time the set and drift could push you 17.5 nautical miles north of your intended port of entry (8 hours and 45 minutes at an average drift of 2 knots). So that means you should start your crossing about 17.5 nm south of your intended target.  That way you could ride the stream north, rather than fight it go due east.

So for a intended port of entry at North Bimini, Bahamas, you would leave from Elliot Key. This would put your total distanced traveled closer to 55 nm.  But since you would likely see speeds higher than your average as a result of being pushed north by the stream, your total travel time would likely be less than 11 hours.

As I mentioned above, the Gulf Stream has varying currents and you can use that to your favor.  Instead of traveling all the way down to Elliot Key we departed from No Name Harbor on Key Biscayne, about 15 miles north of Elliot Key. We took a heading of 145 degrees mag for about two and a half hours after clearing the flats into the Florida Straight. We were doing about 5 knots at 2000 RPMs. About 1/3 of the way through the stream we changed course to 115 degrees mag. We pickup speed to about 6.8 knots without altering the RPMs. We held that course until we were about 10 miles outside of Bimini. This was just about sunrise. We then just aimed right at the North Bimini harbor entrance. This is the classic S-curve approach that is explained well in the front of the Explorer Charts. It took us just under 9 hours for the crossing.

We caught up to three faster boats (Morgan 38 with an oversized motor, Caliber 40 and Pearson 36) that had left at the same time but just stayed on a course of 115 degrees mag from the time they left the flats. So I think this approach was a good one.

When it came to our weather window, even Chris Parker was struggling to get an accurate forecast. We left at midnight as he had predicted that winds and seas would be best overnight at less than 5 knots of ESE winds. He was wrong. We saw 10-18 knots of ESE winds the whole trip. And instead of calm seas less than 2 feet we had 4 foot seas for most of it with some 6+ foot seas in the middle of the stream. For those that haven’t crossed, if I heard 6 foot seas I would think no big deal its 6 foot swell like you get off the coast in Jersey or New England. It was more like the 6 foot chop you can get in Buzzards Bay or Long Island Sound. That was real surprising to me since you are in thousands of feet of water.

Doing the crossing on a Sunday night added lots of cruise ships. We passed 15 of them. Three of the boats in our group had AIS so we could hail them easy and they altered course to avoid us. Same result with the American based cargo ships we passed. The foreign cargo ships were a different story and we had to alter course to avoid them even if we were supposed to be the stand on vessels. AIS seems to be a really useful tool and we might add one down the line. I would recommend it to anyone thinking of cruising the Bahamas or beyond.

The Bimini entrance was well marked. Navionics was also dead on for the depths and channel location. I did put the way points in the Explorer Charts as marks so I had that info to help me too.

After you get to Bimini, your fun isn’t over.  You now have to get across the Great Bahamas Bank.  More on that later.

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