Monday, August 17, 2015

Mariner’s Weather Checklist Before Departure

 It is fundamental to safe efficient weather work at sea that these items be checked off and tested before departure. Having it all onboard without prior testing does not count!

(1) Barometer. This is key instrument to any ocean or coastal passage. Check it over a large pressure range using free service at,  or just interpolate the isobars to get the correct pressure for your location at the synoptic times from unified map at For electronic barometers, you likely have an excellent one in your phone. Use our free marine barometer app, and read the help file that comes with it—a short course on barometer usage. We have extensive notes on barometers.

(2) Wind instruments.  To measure apparent wind speed and apparent wind direction, and they should be calibrated.

(A nice backup to both of these is the small handheld Kestrel 5500. The barometers on these that we have tested have been excellent. It is easy to check the windspeed driving along in a car holding it out of the window. Using one of these to check your onboard instruments, remember that wind at the masthead can be notably different from wind on the deck.  Might have to take it up the mast.)

(3) Calibrated knotmeter and magnetic Compass, and calibrated heading sensor.

(4) True wind from Apparent solution. We need some procedure to convert apparent wind to true wind that is well tested and practiced. This can be done within the wind instruments themselves or some other electronics box they plug into, or it can be done by inputing the data to a computer and computing it there,. Or it can be done by hand with a calculator, which is best done with one that is programmed to do this. There are numerous smart phone and computer apps for this.

(5) Laptop computer. There are certainly ways to do safe weather work without one, but  a computer makes everything related to weather very much easier, more versatile, and better. I would consider it a required item since so many of our best resources are obtained via the computer. In fact since computers are so inexpensive these days, it is not even unreasonable to set up one with all your nav and wx software and connections and then just clone it to another one which you take as a back up.  For PC users, Acer has several very good low cost laptops. Mac users know what is available.

(6) Communications.  This would mean either a sat phone or an HF radio with Pactor modem.  The sat phone is definitely easier, but day to day usage is more expensive.  HF radio work could be near free once set up, but the investment would be notably more than a sat phone to set up from scratch.  It would be nice to have both, that is if the boat is already set up for HF radio then add a sat phone for convenience and dependability.  If not set up already, it would be harder to justify the expense compared to sat phone only.

There are these days all sorts of other communications options, from satellite broadband to systems that connect everything on the boat wirelessly.  However, the basics are in item (6) and they should be there regardless of the other luxuries.  In a sense, the more you have the more that can go wrong, so you want to be able to pick up the sat phone and make a call, or plug it into your computer and send an email.

(7) Software for email. We need software to send and receive emails with attachments… with no restrictions on what we say or include, which rules out the basic ham radio programs. There are numerous options. Airmail from Saildocs is one. Ocens, Xgate, or UUPlus are a couple other options. Each has unique services or features; the prices vary somewhat, but not a lot.

With (6) and (7) in place you can send and receive emails and email attachments by satellite phone.  All of these offer the option in setup to switch between communicating by sat phone or communicating by Internet.  Underway you will use the sat phone, but once in a harbor with Internet, you switch to that.

On the other hand, for getting set up and tested before departure you would also primarily use the Internet connection, but it is crucial that you just spend the air time and do several transfers by sat phone long before departure date. You want to be 100% certain that this system is working, i.e. send and receive emails with attachments. Turn it on and off, computer on and off, reboot, close all, start again, switch back and forth between sending by sat phone and by Internet, try multiple types of files (discussed below), etc. The main point is to be sure this is all working well before leaving and that you have used it for a couple of weeks at least getting your weather information, as outlined below.

Added in June, 2022: We have preached this last point for 15 years, but still find that this is not always done, and very often leads to no communications or weather data underway. This is an avoidable, serious error.  There are many things to get done before leaving, but this one has to be at the top of the list. It is a pity to not have excellent communications at sea these days with all the wonderful options we have. Please do not add another example to the notable list of mariners who did not follow this advice and suffered for it. Beyond weather routing, if equipment fails or a medical emergency occurs, we need communications. Even in a yacht race where outside "tactical assistance" is prohibited, it is still perfectly legal and good seamanship to get help repairing a failed instrument or system.  It is also not uncommon to use up tons of air time on a handheld sat phone getting instructions on how to implement the email system in the computer, which should have been done before departure.  It is then also a sad time to learn that you bought the equipment from the wrong seller and they do not know enough to help you!  So on the prep list is buy from knowledgeable dealers who can help you... and get that help before you depart.

(8) Software for GRIB viewer. Many, if not most, echart programs include the option to overlay GRIB formatted weather data right on the echart you are navigating with, but these are sometimes limited, so supplementing that with an app that can display and analyze weather data is crucial.

I assume you will have some echart program in a laptop for navigation that is tracking your GPS position. Almost any one of these will show grib files for weather analysis. ( If this has not been planned, i.e. you have a console unit from your navigation electronics doing this tracking, then you may want to consider adding the laptop or tablet navigation option. You can do very much more with your own echart or weather app in a laptop than possible with any of the packaged units which are then restricted to just the chart formats they provide as well as limited navigation tools.)

In any event, it pays to have a stand alone grib viewer in your laptop if you do not have one in your echart program. There are numerous options. For the PC there is Viewfax from Saildocs, qtVlm, Expedition, and many others. For the Mac there are fewer choices, but LuckGrib for Mac or iOS remains at the top of the line for both data delivery, display, and analysis.

(9) Source for grib data. Establish and practice with some source of grib weather files. Saildocs is an excellent source. Many of their download options are included in a convenient Viewfax utility called “Get Data”, but they have much other data that are not listed there that must be obtained by email request to saildocs.  LuckGrib has the state of the art data selection, including ASCAT measured satellite winds and OSCAR currents, which others no longer include. See our Weather Course for details.

And again, it is crucial to download some of the files and learn to use these forecasts before departure.

(10) Text forecasts. Don’t forget the text forecasts. Practice receiving by email the crucial text forecasts, as outlined in another note in the references below.

(11) Seawater temperature. When sailing in the Gulf Stream or any other strong current system, or when sailing in the tropics in general, it is extremely valuable if not crucial to have a through-hull seawater temperature measurement, or some other permanent way to continuously read and display seawater temperature.  For ocean currents the water temperature marks the boundaries of various features, and for the tropics the water temperature is a measure of TS development, i.e. hurricane formation usually require seawater > 80º F.


High Seas Forecasts and Tropical Cyclone Alerts by Email Request

Weather by Satellite Phone

Modern Marine Weather

Barometer Handbook

Mariner's Pressure Atlas

Sailor's Logbook



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