I have written a lot about weather up to this point in the book, but in many cases routing for the combination of the prevailing weather and any current or tide can be the most important contributor to a comfortable and safe passage. In this chapter I look at a real passage across the Gulfstream and discuss what to look for and how to react, information that will help you in any ocean with currents.
Managing Ocean Currents
by John HarriesReading Time: 5 minutes
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- Weather Analysis And Routing Is The Skipper’s Responsibility
- React to The Weather, Or Plan For The Weather
- Strategic Weather Analysis—Hardware and Software
- Weather Analysis, A Step-By-Step Guide—Part 1, Tactical
- Weather Analysis, A Step-By-Step Guide—Part 2, Strategic
- Weather Analysis, A Step-By-Step Guide—Part 3, Learning About the Upper Level
- Five Tips For Choosing Weather Information to Believe…And Pay For
- 4 Great Tips From a Professional Meteorologist
- Tips For Receiving Weather Fax
- Tips For Receiving GRIBs
- Tips For Receiving Weather Forecasts
- The Importance Of The Big Picture
- It’s A Forecast, Not A Prophecy
- Managing Ocean Currents
- Iridium GO! Review—6 Myths Busted and a Purchase Recommendation
- The Ultimate Guide to Using Iridium Handsets and GO!
- Iridium GO! and UUPlus, Real World Use Review
- Iridium NEXT Update 2019
It’s posts like this that remind me that I’m nowhere near ready for offshore passages as a skipper. Thanks for the important reminder.
One day, though.
Hi C. Dan,
The situation described in this post, was a particularly complex one so don’t let it discourage you.
And the quickest way to get the kind of knowledge that will help you correctly sort out a situation like that described is to go offshore with an experienced skipper—books, and even this site, will only take you so far.
John, I have re-read this post in preparation for our Bermuda-NY crossing scheduled to start with the first weather window after June 1, and thank you for the insights.
Is there a router who you would recommend to advise on Gulf Stream entry and exit points? Also, may I ask where you captured that excellent colour graphic of the Stream in your post on the loss of Tao yesterday?
The colour graphic was from http://rads.tudelft.nl/gulfstream/
As to a router to advise, I’m afraid you are asking the wrong person in that I feel quite strongly that it is not a good idea to have a weather person making routing decisions, that’s the skippers job and many routers that do offer that service don’t have enough offshore experience to fully understand the implications of their advice out on the water. There maybe exceptions, but I don’t know anyone I can personally endorse.
Having said that, it is well worth while going to an expert to actually find out what the stream is doing. I have always used Jenifer Clark in this regard and been happy.
the graphics on the website you mentioned in your post unfortunately don’t work anymore, the last successful image dates from March 6th, 2019, with increasingly degrading until no data within the 3-4 following days.
Have you got any other source like this?
That’s sad to hear. Jenifer was an amazing source for over 40 years.
The good news is that there are many more sources of GS information available now than the were when I wrote the post, a lot of them in GRIB form. A bit of google searching will yield a bunch of options.
Thank you, John, much appreciated.
I think we are on the same page here. I agree entirely with your point on the skipper’s job, and that this responsibility is not delegable. And that certainly applies to routing decisions.
That said, seeking knowledgeable advice, and weighing it with other material factors — including the advisor’s abilities and limitations —knowledge of the capability of the vessel and its crew, etc. etc.,, is central to this process, as it is to all executive decision-making. Seeking advice is one thing, what one does with it is another.
As you have underscored in other posts, (e.g. The Best Weather Forecast You Never Heard Of) wx forecasts themselves are opinions to be considered, and it is invaluable to understand what goes behind them; the same applies to across the board.
Thanks for sharing your insights from your thirty and more years of Stream crossings. I can see another seminar in the making there, if you were so inclined . . .
Very nicely put, better than I did, as you say, we agree completely.
I should be interested to know the science/mechanics behind the wind against current phenomenon. Googling the question was a limited success, with the only explanation which made sense referring to the effect of the wind on the elliptical movement of the water in waves. The deeper water continues pushing forward, while the higher water is pushed back by the wind, leading to steeper and breaking waves. Do you or any of your correspondents have a better explanation for the phenomenon? There are a number of shallow water examples around the British Isles, the Portland Race probably being the best known, but I have never had the misfortune to experience one of the major ocean currents.
As an aside, and because I agree with the argument that skippers should learn to interpret weather data from the level of the deck, I have been learning a lot from this book written by a professional mariner: http://www.chesneaumarineweather.com/?p=214
Maybe a stupid question, but I’ll ask anyway. My wife and I cruise in a powerboat so I know what speed to expect for a given rpm in calm water. If, for example I normally cruise at 10 knots and I am now only making 8 knots, can I conclude that I may have up to 2 knots of current affecting me? In other words, is there a direct correlation between my speed and the current? My gut tells me yes, but I cannot find a real world statement confirming this.
I’ll give you more details if you’re interested, but I ask the question because we just had an experience going from New Zealand to Australia. Instead of going our usual 10 knots, we were only making 7 knots as we got into the Eastern Aussie current. This was going on for about 24 hours. Winds were 10-15 knots directly on the starboard beam. Suddenly the wind increased to 30 knots and the seas built rapidly. We then had the closest thing we have ever had to a rollover. I made a number of stupid mistakes and piloting errors. I am trying to get some insight into how to predict current in a real time/real world situation and want to make sure I am making the correct assumptions. BTW, the forecasted current speed at the time in our location was 1.3 knots but we had a boat speed reduction from normal of 3 knots.
Not a stupid question at all. Back in the days of dead reckoning this was one of the hardest things for new navigation students to grasp since it’s not that simple. To be able to calculate what the current is we need to know both the difference between speed through the water and speed across the bottom and the difference between heading (the way the bow is pointing) and course actually made good.
With these inputs the traditional method was to construct a vector diagram on the chart to determine current direction and speed. Today there are computer programs that will do the same thing, and there’s probably an app for that.
Also, some plotters and nav programs will read out current speed and direction but that does require a speed through the water sensor, typically a paddle wheel type.
The point of all this being that if you are experiencing say a 2 knot speed drop it could be a 2 knot current right on the bow, but it could also be a stronger current say 45 degrees off the bow.
As to your experience with a much higher than forecast current, this is not at all unusual in areas of the ocean with a standing current. For example I have seen as much as 6 knots in localized areas around the Gulf Stream. The key to identifying and avoiding these areas is water temperature, both measured on the boat with a sensor and imaged by satellite. Typically high currents will be around places where there is a rapid change in water temperature. This is much the same mechanism as a front in the atmosphere.
Back in the day when I navigated ocean races we spent huge amounts of time studding water temps and even average sea surface hight to gain a favourable current advantage or avoid a foul current.
Thank you so much for your thoughtful reply. This is the best explanation I’ve had and it makes total sense. BTW, you and your blog are such a resource for cruisers, thanks for all the effort.
Thanks for the kind words. One other thing I should add is that extra fast currents are also found in places where the core current makes a turn. Again, these can be identified and avoided with water temperature imaging.
There’s a really great pamphlet on navigating the Gulfstream. It comes from a collection of articles written in Ocean Navigator magazine from 1987 through 1994. You can buy it on Amazon:
Sounds like a good recommendation, thanks.
Currently unavailable on Amazon, found here: https://www.abebooks.de/servlet/BookDetailsPL?bi=30514753717
Thanks John for this and all your articles, including the ones comparing the Garcia and Boréal which first led me here. My first comment/question is this: how do you get accurate waypoints off of those little online gulf steam charts? Tell me it’s not just guesswork based on given Lat/long Lines?
Yes, estimates from the lat and long grid. Fine for our purposes because the underlying data was not that accurate anyway. When racing we used to refine our understanding of what was actually happening by measuring water temperature. These days you will be able to get data with a higher granularity, but it’s very important not to confuse display accuracy with actual accuracy.