Thursday, February 28, 2013

Logbook Procedures

Navigators and vessel owners usually have set ideas about logbooks and recordkeeping underway. They vary from the most formal (pondering the notion of the ship’s log as a legal document) on down to none at all (pondering… or rather, not pondering anything). A visit to Captains Nautical Supply store today found some two dozen logbook options for sale, varying from 2 x 3 inches in size to almost 2 x 3 feet in size. The preprinted forms included varied from blank lined pages to amazingly complex patterns of forms and tables to be filled in.

The choice inevitably has to be personal, but I offer here some guidelines to what has worked for me and then come back to the legal matters alluded to above. For an ocean voyage I typically have three logbooks. One is the ship’s log, or deck log, which is the normal logbook referred to above. Every vessel should have one of these for all voyages and day sails. This is best done with some structured layout in a bound book. We will come back to what goes in it, and when, and why. To this basic logbook, I like to add a weather logbook and a third bound book, which could be called a notebook or a logbook.

The weather log is for transcriptions of voice broadcasts or a place to paste printed forecasts or maps, and generally a place for notes about the weather. This can be just a blank notebook. Numbered pages are nice for cross reference. Make entries sequentially from the front, and record the date at the top corner of the page. Try to avoid setting up some coded system of starting a new section in the back. Dated pages in sequence are always best. It will grow to be one of your most important books. Even on a day sail or race, you will have a set of VHF weather reporting stations you care about. You can record these in the broadcast sequence and record the reports in columns to watch how things change throughout the day. Remember the Marine Weather Service Charts explain all weather resources in your area along with their schedules (see You can also make notes on your own observations related to weather that are too specific or personal for the ship’s log. It can also be the place you make a time schedule of when various reports and forecasts are available for quick reference so you don’t miss any. This is a deceptively challenging task, discussed in depth in the book Modern Marine Weather.

The third book is a navigation journal of sorts. A place to do all general reckoning related to the navigation of the vessel. In other words, do not use scrap paper. All computations go in this book, no matter how simple—if something ends up not making sense, the paper trail can be helpful. Also record your observations and insights along the way that improve your navigation. Navigation knowledge proceeds much faster with a written record. You may learn some trick about radar tuning, or how far you can hear a buoy gong in certain sea state, etc. When you do a piloting fix there are always pertinent notes that can be added to describe it. At the end of the voyage you can then go back over what you learned. Sometimes I find these books that are 20 years old and discover when I first learned something that I now take for granted—or relearn something I had forgotten about. Though I discovered the value of this extra logbook by experience, I have since learned that the US Navy uses the Navigation Workbook (OPNAV 3530) for exactly the same purposes, so this has proven value in prudent navigation.

This book need not be for navigation alone, it could be for other matters of seamanship you picked up on the voyage. I recorded once, for example, a fantastic knot that I learned from an experienced sailor, and to this day I have never seen that knot in any other book. Again, sequential entries from the front with dated pages are best.

If you sail on a race boat with a lot of crew, boldly mark your notebooks “DO NOT USE FOR SCRAP PAPER,” otherwise you will find pages torn from them at random.

The ship’s log, however, is the main point at hand. The bare minimum it should include is time, date, position, course, and speed, entered every 4 hours or so. A more appropriate and useful log would include more columns and be entered more often.

The design we use ( is two-up letter size pages with 30 numbered rows. Columns on the left hand page include Date, Time, Log reading, Tack, Course (compass), Speed (knotmeter), Lat / Lon, and then 3 columns without headings for your choice of data. The usual ones I use here are COG, SOG, and WCV (waypoint closing velocity), which may have different names depending on your GPS model. In some cases you might want to change this to VMG, which is progress relative to true wind direction. The thin column for tack (P or S or M for motor) would seem redundant with the wind and course data we have, but it is still often referred to. It is best to record actual compass course and knotmeter speed (instead of just COG and SOG) because these are the data you will need to check your previous DR if you end up without GPS.
On the right-hand side we number the rows again 1 to 30 and the columns are Apparent wind speed, Apparent wind angle, Barometer, and Comments. We also ask that the person filling in the log put their initials in the Comments column or beside it. If you have true wind instruments and are confident they are working properly, you could record true wind instead of apparent.

The comments could be weather or sea state notes—these are ones related to the navigation at hand, as opposed to general matters of weather and forecasts in the weather log—sails set, when you charged the batteries, if you sight or speak another vessel, fridge or freezer temperatures, etc. Sailing anywhere near the Gulf Stream or similar currents around the world, the sea water temperature would be another key factor to log. I have never recorded or found much use for air temperature outside of the Arctic, but the full picture would include the outside air temperature. Certainly if you are sailing in very high latitudes, the air temperature becomes crucial.

When to enter the log is easy. Make an entry anytime something changes. An average steered course change of 5° is a lot, and calls for an entry, as does a change of speed by a knot or so. Racing sailors tend to make an entry every hour, which is helped by the numbered rows. If not entering on the whole hour, record the time in the row with the nearest hour. This way the several watches can carry out distance made good contests per hour or per watch. When cruising it would be unlikely to enter every hour, but on any voyage the rule is at least every four hours, even if nothing changes, and if something does change make an entry. Keep in mind that if all your electronics fail, your latest logbook entry determines your navigation knowledge. In an emergency or near landfall you will be happy to have this be recent data.

You will also find that in doing weather analysis underway it is crucial to have a log entry at the synoptic times of 00, 06, 12, and 18 GMT, which are the times the weather maps are valid. Then you can compare your barometer and wind with the weather maps. You might set your watch alarm to remind you in local time when these entries should be made. Remember, too, the free service Starpath offers to provide you with live weather data at sea from ship reports. Send an otherwise blank email to with the word “help” in the subject line to learn about the service. With this you can get all the ship reports within 300 miles of your (or any) position over the past 6 hours. Do this an hour or so after synoptic times to check your barometer and weather maps. You can also read about this at

If you are on a route to a foreign port in a vessel of any size, or your vessel is over 100 T in local waters, then 46 USC §11301 ( explains the legal requirements for logbooks, which are indeed rather elaborate, though the regulations are addressed mostly to safety issues, along with the makeup and behavior of the crew. Specific types of vessels have specific logbook entry requirements, although navigation entries are not addressed. Logbook procedures for Sailing School Vessels, for example, are covered in CFR 46 §169.841. We learn from all these required procedures that we might want to include in our non-required logbooks a couple of pages to list:

• Departure and destination
• Documentation or registration number of the vessel
• Draft of the vessel
• Names and nationalities of all crew members. (If you are sailing into foreign waters you should also know if any has been convicted of a crime.)
• List of the safety drills and inspections you have carried out, station bills established, and a statement that all crew members have been informed of the safety procedures on board.

Furthermore, it is not really an option as we learn from 46 CFR §78.37-3, Part (b): “The master or person in charge of a vessel that is not required by 46 U.S.C. 11301 to have an official logbook, shall maintain, on board, an unofficial logbook or record in any form desired for the purposes of making entries therein as required by law or regulations in this subchapter. Such logs or records… must be kept available for review by a marine inspector for a period of 1 year after the date to which the records refer.”

I must admit that I have never sailed on an ocean passage in a yacht where these data were specifically included as part of the ship’s log, but the virtue of the addition is clear in the event there were an accident. It could also be helpful in some port operations in foreign waters. On the other hand, there have been many times I wished in retrospect that we had kept a list of the crew members we sailed with on specific voyages. These records can also be valuable to crew members who one day want to apply for a USCG deck license, as this book can then help document their sea time.

You might also want to start a logbook numbering sequence for your vessel, so that as you sail more there is an order to your sequence of logbooks. The USCG offers a free copy of their Merchant Marine Official Logbook for those who are required to carry one. It is called CG 706B. It contains much information and references, but it is not very useful for small-craft deck logs. The master or owner of a sailing vessel on international routes may want to request one and read the official requirements. If you are playing Nautical Pursuit and need this answer, this is the place you will find the phrase “the ship’s logbook is a legal document,” but admiralty attorneys will still remind us that this is an imprecise phrase. §

Sample Pages from the Starpath Sailor's Logbook

Saturday, February 23, 2013

Final Word on Relative Humidity and Dew Point

After a long, painful, and expensive study of these subjects over the past year, the conclusion is not a happy one, and ironically it is exactly the same one I came to in the mid 80s...which is a commentary on something, but I don't know what.

Below is an executive summary, which you can read and then move on––and save yourself another 30 min on this topic. All that will follow the summary is just the justification for the summary, and the background needed to understand it.

Our perspective is always that of a mariner, looking for weather knowledge that will enhance the safety or efficiency of navigation.

Although the moisture content of the local air mass is a fundamentally crucial factor to the weather you will observe, local relative humidity (RH) values that you might measure or be told by someone else have no practical value to your weather work at all.

The numeric value is way too sensitive to immediate conditions (ie several feet, several seconds), in large part because the number is so sensitive to air temperature. Thus we do not need to include at this point any discussion of how to measure it.

Measured dew point could in principle be of some value in predicting the onset of fog in the rare case that this might aid your navigation and when isolated from any wireless communications. With communications to landbased resources you could likely obtain a better forecast for your location than you could make yourself. This measurement requires a good sling psychrometer using careful procedures (most packaged instructions are not adequate). You do this by measuring the dew point and air temperature over a period of time to see if they are converging, and then if nice linear lines are headed toward each other, you can project to the time they will meet and likely make fog.

On the other hand, we have such wonderful online resources these days, that we can actually look at this type of data from around the country and see that this does not always work. The two numbers could approach each other all late afternoon and evening and then just change directions before they meet. Fog often forms when the air cools at night on clear days.

In short, we are better off simply understanding this principle and not hope for any practical application of our own underway.  The amount of effort and equipment to do it right cannot be justified by the success rate you might obtain.

Thus we should just give up on these two topics and devote whatever time and resources we have to barometric pressure, which can be measured very accurately with the right instruments, and the results are indeed extremely valuable to our navigation. The same can be said of properly calibrated wind instruments. Wind instruments on many vessels, like barometers, are more often not calibrated than calibrated. We see them change and assume they are right. When they are not calibrated, we do not get the most useful information from them, and thus eventually lose perspective on how important they could be.


Relative humidity is indeed important for good health at home, and crucial to protecting good cigars and musical instruments, and there are ways to measure that with a useful accuracy, which we will add valuable information later on below, along with the pictures and data from our last round of measurements, which are just wrapping up. (Notice the word is "last," not "latest.")

More to follow...

Sunday, February 10, 2013

Obtaining Ocean Current Data Underway

We have several links in this blog and elsewhere that describes the importance of ocean currents on any low-powered craft crossing an ocean.  This factor is even more important than we had realized just a few years ago. New satellite data and enhanced ocean models have shown that there are numerous mesoscale eddies (30 to 300 nmi in size) that can have remarkably strong currents, up to 5 kts in extreme cases. Thus to do the best we can in ocean navigation we need to learn as much as we can about the ocean currents.  It is not just the Gulf Stream where these things matter.

Near US coastal waters we have the HF-radar measurements, which remain the primary source of data in those regions, but in the open ocean we must rely on the interplay between isolated rare measurements of actual currents from buoys (drifting and fixed), combined with extensive satellite measurements of sea surface heights, all folded into some numerical model of the ocean’s motion as driven by actual winds, also measured by satellites (ASCAT, OSCAT), along with global models of the weather patterns (GFS, ECMWF).

There are several ocean models in use whose data are available to mariners underway. For now I just want to compare some that we have looked at over the past week or so. My main reason for presenting this is so we have the examples in hand that can be viewed by the experts, so they can  guide us onto the best path. I must confess no real knowledge on what is the best possible approach.

I do know that one model has forecasted an eddy that we can definitely see the effect of at this moment on the rowboat JRH west of the Cape Verdes. That alone is plenty of encouragement to keep on trying to learn more.  In fact, there is an even much larger eddy one week in front of this boat, which will be another test.

We have been using data from the Hi-Res Atlantic RTOFS model, updated daily at 16z, with the vessel position overlaid on the current forecast pages (the work of Angeline Pendergrass).  We get this data by a custom procedure that is not a public tool, but I have just learned that there are several public tools for getting related data underway. Both work well and both are free services provided by their authors. There are also several commercial products available, one of which we have access to and can compare.

The goal now is to compare these sources of current data for specific times and places, as well as provide references to where mariners can obtain this data on their own.

The following pics are RTOFS foreasts for 00z on Feb 10, 2013 for a small region west of Cape Verde. The top is from the data set we are using (Hi-Res Atlantic RTOFS) which is where we were warned of the upcoming eddy. We do not have specific current measurements underway due to a missing component of our data stream, but we have convincing indirect confirmation from much enhanced speed made good that correlates with the eddy location. In fact, at one point recently the vessel was on sea anchor in 20 kts of NE wind, making good a drifting course to the NW of almost 1 kt.

Below is the same model data but looking a bit more forward on the same date, followed by the same predictions from another source.

The boat is now located in the patch of the small eddy in the bottom right of this picture. This had been much stronger current, but it is now weaker though still predicted to be 2 kts to the SW. Some miles ahead we see a much bigger eddy that has patches of 5 kts of current predicted.

Both of the above pictures have been downloaded and processed by the OARNW team. The data are readily available, but these pictures take some manipulation to produce. It is not public service.

Below are data from a similar model (RTOFS Atlantic vs RTOFS hi-res Atlantic, used above) which are readily available to mariners underway from the program. They can be requested from within the ViewFax Grib Viewer (Ver. 5.0.56), which is the work of Pacific Northwest sailor Jim Corenman.  The free program is available at This is the GRIB Viewer that is used by SailDocs, familiar to many mariners for viewing model wind forecasts and weather maps, obtained by SSB or SatPhone underway. The system is very nicely organized for data selection and for trimming area and resolution to save air time in downloads.

This sample covers the same region as above. He offers the data every 12h for 5 days. This is plenty fine enough temporal resolution for most applications. When using the program, be sure to crank up the resolution to the  highest available.

To illustrate this best, we show here all 10 pictures so you can roll through them to see the eddies move. Just click anyone open to get into the blog picture folder then mouse scroll though them to make a movie. There are clearly huge currents here, but i do not have a color code made yet.  The purple is 3 to 5 kts, reds are 2 to 3 kts, yellows about 1 kt.

We have also just learned of another way to obtain  ocean currents forecasts on a global scale when underway, and that is with the Ocean Model OSCAR. Another Pacific Northwest sailor has made these data available to us at  He has designed the system to match the saildocs procedures, but this data and serivce is completely independent of saildocs.  The procedure to get these files by email request is described on the SV Sarana website. In principle a GRIB file could be viewed on any grib viewer but the various ones that are popular are not always compatible. The OSCAR data from this source work fine in the ViewFax grib viewer.
same one used to view the above data.
The OSCAR model is run once a day, but it is each time an average over the past 5 days. We are not sure yet what the significance of that is. The RTOFS data certainly implies the currents are more complex than we would want to average over, but we do not yet have enough specific confirmation  that the predicted details of the RTOFS are validating. So far we just know that there is definitely strong current in the location and direction predicted.

The picture below is for the same location, but instead of looking ahead 2 days as we have done above, this one has to look back and tell us the average over the past 5 days. After having watched the RTOFS eddies for the past 2 weeks fairly carefully,  I am  surprised  they do not match better on the 5-day averages. The RTOFS eddies have been clearly persistent for 5 days.   It could be i am not getting the OSCAR data properly. These are also also grib data, so we can move the cursor around on the plot to ready current speed and there is rarely any over 2 kt on this picture.  I will take then for the next few days and add them below.

We have to study this more. There is one note on the OSCAR website that they have optimized the model for the Tropical Pacific.

[ Added Mar 23, a new Comparison of Ocean Models ]