The Offshore Voyaging Reference Site

Tips, Tricks & Thoughts:


  • Gales at Anchor Are Not That Scary

    I don’t watch a lot of videos, in fact hardly any, but I was searching for something else when I stumbled on this video over at S/V Delos.

    Now, there is no question that hurricanes are scary. You don’t have to tell a guy from Bermuda, who cruised the western North Atlantic for over 50 years, and now lives in an area of Canada sticking out into the frequent path of hurricanes, that.

    And the couple on Delos were seamanlike in moving quickly to find a good place to ride the blow out, as well as being flexible in changing their plans when the storm wobbled.

    All good.

    But the majority of the video is about riding out the storm and is filled with drama.


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  • Q&A—Weather Information In The Southern Hemisphere


    Member Terence asked:

    When we went to Polynesia, we used Predict Wind. We could get weather in all latitudes. Next year we will again be sailing south of the US Pacific Ocean Prediction Center maps. Need I again use Predict Wind to get what I need? Someone asked the same question about the south Atlantic. I think you did not have an answer. I would like to follow your advice, but I need to figure out how to get information in lower northern latitudes and perhaps south of the equator. Or do I just stay with Predict Wind?


    Predictwind is just a tool for downloading and displaying information generated by government models (with some interpolation in inshore areas). So I think it’s easier to first think about the underlying data.

    Once we have that sorted we can pick the tools to get and display the information that best meets our needs.

    Login to continue reading (scroll down)

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  • Great Weather Product

    The good folks over at the Ocean Prediction Center have a feature on their weather-maps page to cycle through weather maps for the last 3, 7, or 14 days.

    A great way to study how systems are moving and evolving over time in the area we plan to cruise or the ocean we plan to cross.

    • It’s important to understand that this is historic (before today), not forward looking.
    • It’s easier to understand what’s going on if we slow it down, or better yet stop it and use the buttons at the top to step through at our own pace.

    Don’t let the historic nature of this tool put you off. Knowing what the systems have been doing for the last two weeks is invaluable when planning cruises and voyages.

    And those who have taken the trouble to learn a bit about 500-MB weather maps will get even better insights by looping those maps.

    Other useful options are to add satellite imagery and look at how waves and swell have developed over time.

    A truly great learning tool for anyone who wants to really understand the weather around them, rather than just looking at GRIBs.

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  • PredictWind Unlimited With GO! Exec Better Than I Thought

    A few weeks ago I wrote a Tip pointing out that the “unlimited” air time package for Iridium GO! exec was not actually unlimited and therefore I recommended staying with the truly unlimited package available on the original Iridium GO!.

    I have now dug into this in a series of emails with Craig and Matt at PredictWind.

    The result is that, although I was right that the unlimited package does have limits, if we put aside semantics it sounds like a good deal that will enable users to download and analyze the weather, in the way we recommend, for known costs.

    This Tip is focused on PredictWind’s capabilities as they relate to the techniques we recommend in the above-linked Online Book. It’s not a review or a recommendation to go with PredictWind or buy an Iridium GO! Exec. That’s up to you.

    Here’s what an offshore sailor will need, what it will cost, and the capabilities delivered:


    Hardware (one-time cost)
    Iridium GO! Exec with DataHub and external antenna$1,999
    SIM Card$10
    Monthly (ongoing costs)
    PredictWind “Unlimited” Data Package$170
    PredictWind Professional ($499 / Year)$42
    PredictMail ($119.95)$10

    All in US$. Monthly costs rounded up. The standard PW package at $249/year will do, but if we are going to do this right, we might as well go the whole hog.


    1. Up to 4MB of GRIBs a day (plenty).
    2. Unlimited email, including attachments (to download weather maps and forecasts not offered directly by PredictWind).

    Confirming #2 with the folks at PredictWind was the primary reason I wrote this Tip.

    Other Benefits

    • The Iridium GO! Exec is much faster than the original GO!, but not really fast enough for true internet access, which Starlink is.
    • GO! Exec can be used to make a phone call without using a linked cellphone, which makes it far better for emergency use, particularly in a liferaft, than the original GO!.

    Watch Out

    We are only protected from cost overruns with Iridium GO! Exec and the PredictWind “Unlimited Package” as long as we stay within the PredictWind apps listed above.

    If we turn the firewall off to get true internet access, we will need to buy added data packages, which we may blow through in minutes.

    The unlimited package on the original Iridium GO! is truly unlimited, albeit much slower.


    The above is based on an email exchange with PredictWind. I have not tested any of it.

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  • Beware AI-Generated Weather Maps

    I have repeatedly recommended looking at forecaster-generated weather maps, as well as GRIBs, to get an overall understanding of how weather systems, and particularly fronts, which are not drawn on GRIBs, are developing.

    But wait, lately some of the GRIB-viewing tools have added AI-generated fronts. So can we now not bother to go through the hassle of downloading weather maps?

    Two pictures are worth a thousand words:

    The one at the top of the post was AI generated.

    Now let’s look at the real thing from the same time:

    A quick glance shows that the AI version misses a huge amount of vital information that’s on the human-generated map. At least nine—count ’em, you may find more—developing gales, as well as a bunch of fronts, are shown on the real map that are missed on the AI-generated fake.

    I could go on for a couple of thousand words on how much better the real thing is, but do I really need to beat that dead horse when one glance shows the clear superiority of the real thing?

    That said, the most important advantage of the human-generated map is that it shows where lows are developing on the fronts, as well as the type of front: warm, cold, or occluded.

    And if we don’t understand that last paragraph, we need to learn more about weather basics before we take a yacht to sea…and regularly looking at weather maps is the best way to do that…as well as reading this:

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  • Original Iridium GO! Still a Better Deal Than Exec

    There’s a headline to provoke screams and tearing of hair.

    After all, the new Iridium GO! Exec is 40 times faster than the original GO! and only twice the price, so it’s gotta be the the better deal…right?

    And you can get unlimited data with the original GO! from lots of places for $154.95/month and unlimited for the Exec from PredictWind for $169.95, just a $15/month difference.

    So at this point you must be thinking that the old fart who runs this site has finally and completely slipped his cams when writing that headline.


    As so often in these things, the reason that GO! original is still a better deal than Exec is in the fine print.

    Look at the screenshots at the top of this tip, and see if you can spot it.

    You got it, with the original GO! unlimited plan you get unlimited data minutes for:

    • Email
    • Snapshots of any page on the internet: news, stock prices, whatever.
    • Weather maps unavailable from PredictWind.
    • Really vital weather information unavailable from PredictWind—more in an upcoming article.

    Anything we want, any time we want, as much as we want.

    Sure it’s slow, but so what, we don’t have to stand there and watch it, at least if we use decent software to run it.

    We ran this business, including a ton of email, when out of cell phone range on the original GO! unlimited data plan, and downloaded a bunch of weather data, without ever needing to use more than an hour or so a day.

    But with GO! Exec the “unlimited” is restricted to PredictWind data only!

    Yup, the way I read it, after we buy the “unlimited” package for $169.95/month, we need to then add a data minutes package if we want anything other than stuff from PredictWind.

    And it’s not even clear to me that we would be able to get our email under the “unlimited”.

    So sounds to me like we are going to need to buy say 10MB (not going to go far) for another $40 if we want to venture out of the PredictWind world, and maybe even if we want our email within it.

    And note they are charging data by the megabit, not connected time, so the much vaunted speed of Exec is not going to help.

    Begs the question: when is unlimited, limited?

    To make this worse, in their Exec FAQ, PredictWind claims that the unlimited package avoids “bill shock”. But what happens if you don’t buy an added data package, or do and go over it? Don’t know for sure, but I also don’t want to be the one to find out!

    My Recommendations:

    1. Stick with original Iridium GO! and the unlimited plan.
      • I know for sure that package is…unlimited. In several years of use for anything I wanted, including sending super-stupid grinning selfies to my daughter, there was not one single added invoice over and above the unlimited monthly charge.
    2. If you really need a fast solution? Go Starlink as well.
      • Exec, even 40 times faster, is way too slow to actually do anything useful on the internet.
    3. And if you need a solution to take into the liferaft, something Exec does do better than the original GO!, buy a secondhand Iridium handset.
      • There should be plenty around at good prices from people who bought limited unlimited.

    Limited Unlimited?

    One final thought:

    It would be nice if Iridium and PredictWind would be a bit more careful with the word “unlimited”. On this page they specifically write “Unlimited Data”.

    Look it up in the dictionary, guys. The way I read it, “unlimited” means without limits or restrictions. And “data” means all digital data, at least to me, not just that originating at PredictWind.

    I just can’t see how you can be a little bit unlimited, or a little limited when you’re unlimited…OK, I’ll stop.

    More on how we downloaded and analyzed the weather using the original GO!

    This Online Book needs updating. It’s on my list for this winter. That said, the fundamentals are still relevant and can save you a lot of weather-related grief.

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  • Blocking Highs, Love ’em Or Hate ’em

    As I write, the North Atlantic is a weather hot-mess with hurricanes and gales dotted all over the map, and yet all the models are predicting an incredible run of settled early fall weather and light winds for Nova Scotia, extending out ten days or more.

    What’s going on?

    We in Nova Scotia are falling under the protection of the weather-godfather of upper level systems: a blocking high.

    I’m loving it, since I can go rowing on quite cool mornings and sailing in the afternoon when the sea breeze kicks in on our lovely Mahone Bay.

    But if we are trying to make a passage under sail in the mid-latitudes, we will hate a blocker for its light winds. And if we are to the west of one in the northern mid-latitudes, it’s likely we will hate the stationary low pressure over us that’s blocked from moving away.

    In either case we can use this understanding to make better strategic decisions than we ever will from just looking at a surface model.

    I was about to start decommissioning our boat for winter layup, but have delayed that, and back in the day I used this information to make our cruises more comfortable and safer.

    That said, I have radically oversimplified, as is fitting for a Tip, but if you want to understand how to manage your voyages strategically, rather than just looking at models with no understanding, we have an Online Book for that:

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  • Q & A: Iridium Go! or Go Exec


    The new Predict Wind Iridium Go Exec device does indeed have a subscription plan that limits data according to how much one pays, i.e: $159.95/month buys you only 50MB of data. That includes all data transfer including tracking data.

    Do you happen to have a clue how much data you found that you used, on the average, per month with the original Iridium Go device?

    I am just trying to figure out what size plan would be needed in order to not have to worry about constantly hitting the ceiling towards the end of the month. I believe you & I would have similar usage (that is forecasts & basic emails).


    The exact amount of data we used varied a lot, so I don’t think that’s the way to make the decision.

    Rather, what I can say is that we never had a problem getting all the weather information I needed, and I download a lot more than most people, as well as being able to handle all of our email, which, again, is a heavier load than most people, because of running AAC.

    Sure, sometimes the GO! took as much as an hour to deal with all that, but so what? With good software you don’t need to sit around and watch it, and if there’s a drop-out it reconnects automatically and continues on until done.

    So if it were me, I would stick with GO! to get the unlimited plan, given that I just don’t want the stress and aggravation of worrying about a hard data limit and the huge charges if that gets inadvertently breached.

    I also would not want to have to figure out how to buy more data if I ran out while at sea.

    So given that GO Exec is not fast enough to surf the internet, and does not have an unlimited data plan, I just don’t see the point of it against the original GO! with an unlimited plan.

    That said, as I have said before, being able to make calls without the kluge of a connected smart phone is a nice upgrade, but not enough to push me into Exec. Rather I would recommend buying a secondhand Iridium handset for the emergency call function.

    More on exactly how to use G0! For both strategic and tactical weather forecasting.

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  • New Iridium Go! exec

    Predict Wind have a preliminary announcement video for a new faster version of the Iridium GO!.

    Not a lot of details yet, but it’s supposedly a lot faster, although not fast enough to use for actual internet surfing.

    The big drawback will be if the unlimited data package available with the original GO! is not offered with this new unit or is a lot more expensive.

    I’m guessing it might not be the great deal that the unlimited plan on the original unit is since the new GO! uses the Certus modem like Iridium Pro.

    If no unlimited plan is offered, or a much more expensive one, I’m thinking that for many users who are just looking to download email and weather information at sea the original GO! may still be the best option since I have never had any problems getting all the weather data and email I need over the older unit.

    Definitely the key thing to look into and clearly understand before purchasing one of these new units is the availability and cost of an unlimited plan.

    One upgrade I did like is that the new unit has a speaker and microphone and so can be used for telephone calls without connecting a smartphone. This is a big safety benefit since there have been incidents with the old GO! where users were not able to get voice communications working quickly in an emergency.

    Here’s the intro video, not that it’s much use:

    And here’s a Q&A that might be more useful.

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