Friday, July 20, 2018

USCG Deck Exam Questions at

The database of thousands of USCG deck license exam questions is one way to get extra practice with most types of navigation problems. We offer a unique interface to these questions to all students signed up in any of our online courses. This free option is not part of our regular assignments, and not all participants choose to use them,  but the resource is available, and we do offer support on the solutions, so long as they are within the realm of navigation or weather. We do not offer support on the questions for deck general or safety, or things like that.

Our interface is unique in that you can chose random questions from any of the groups (Rules of the Road,  Deck General,  General Navigation,  Safety,  Navigation), or you can create custom practice quizzes to your own design.

For example, you can ask for all Nav Rules questions the USCG has ever asked on the subject of Barge Lights; or ask for all cel nav questions on amplitude; and so on.

Below is the part of the first page on a query on "barge" for inland rules. You could to the same, for example on the words "narrow channel"  or "fairway."

Here is another example asking for "extinguisher" in the Safety dataset. Again, you can ask our instructors for help on the barge lights, but not the fire extinguishers!

Beside the option for random or user-designed quizzes, we have prepackaged a lot of the common topics asked for, as noted below:

There are thousands of questions, so if you want more practice, you have got a lot of options. To work the cel nav questions you will need a 1981 Almanac, and to work the tide and current problems you will need several specific outdated tables, which I think we have pdf copies of if needed. We do not have much call for that since we cover those topics thoroughly in our own materials.  Most of the others nav and weather questions are generic.

How to get access to the questions

Enrolled students can just post a note in their respective Student Discussion Forums and we will provide the access to you.

If you are not enrolled in any course at the moment and do not have an active webcard, then you would need to either purchase a webcard, or extend your existing one.

Note that many products we sell automatically include a webcard, which gives you access to the custom or random quiz generator—to make it random, just choose a dataset and submit with no keyword. The webcard, provides access to all of the resources listed as well as the opportunity to post your own questions to our instructors in the Public Discussion Forums.

The quiz generator is in the Resources section, under Library / Practice Problems.

Here is a note on the history of the public access to these questions.

I want to stress that Starpath School of Navigation is not focused on USCG license exam preparation. There are many experienced facilities around the country that are USCG approved for that purpose. They are a better resource if a license is your main goal. They issue the tests themselves, so they know the best way to teach what you need.

We offer these questions to our students (as they appeared when last in the public domain) only for the purpose of providing optional extra practice—and we offer support on how to solve these problems.

Note on USCG Exam Questions

USCG deck license exams are made up from their database of questions. In the past, every few years they have made up a dozen or so exams for each license or upgrade, covering a list of specific topics, with different numerical values in each of the exams.  For those who need to pass one of these exams, the traditional method of study is to get access to the data base and work through enough examples that any random sample of that type of problem can be solved. The test time is limited, so this type of practice is crucial. There is not enough time to figure out what exactly they want, and how to best solve it.

The deck questions are in these groups. There are a couple thousand questions in each set.

Rules of the Road
Deck General
General Navigation

As a historical note, all mariners owe a debt of gratitude to Richard Block of Marine Education Textbooks in Houma, LA, a company that remains Central Headquarters for license preparation training materials. In the late 70s and early 80s, Richard founded the National Association of Marine Educators (NAME) to coordinate, among other things, the study of USCG exam questions, as there were notable errors or misleading questions that affected the quality of the testing and indeed the lives of those mariners whose jobs depended on passing these tests.

As part of that project, he worked for seven years through the Freedom of Information Act to force the USCG to release the database of questions to the public, just as other federal testing agencies had done. He won that long battle, which led to an improvement of the questions as they could then be checked by many professionals, and this has indeed had a major affect on license training preparation that persists to this day.

 (As a historical insert here, in those days, we at Starpath still had one leg in the academic world with top of the line computer resources, so we were likely the first school that could actually read the then classic large magnetic tapes in Fortran format—the USCG released the data reluctantly in a format they did not expect to be decoded. Here is the kind of computer needed to read the tapes originally provided by the USCG.)

Once the internet became established and folks expected better service, the questions became available in Excel format online, and sometimes as pdfs. At times they became unavailable, then back on  again at the USCG website.  However for several years now they have been totally removed with no further promised access to them.  Richard has retired, and it is doubtful in these modern times that anyone will spend the huge effort needed to pursue this.

The USCG do periodically update or add to the questions, and there were recent changes in response to new Inland Navigation Rules. There are now many third party sources available online, but usually with little background provided on what they are offering. It is not a surprise, however, that available datasets do still contain many errors—not so much the content errors that Richard was pursing in the past, but now more format and spelling errors.

Although there are still what we would call poor or outdated questions in some areas, all in all this resource remains a valuable way to hone your skills in navigation. Especially with regard to the Navigation Rules. You can argue about some questions, but it is fair to say that if you can pass a test of 100 random questions on the Rules with 90% or more, then you must have a good understanding of the Rules.

To work the cel nav questions you will need a 1981 Almanac, and to work the tide and current problems you will need several specific outdated tables. Most of the others nav and weather questions are generic.

We offer a unique interface to all of the USCG questions at  Students signed up for any course have free access to all of them;  they are also available to anyone with an active Starpath webcard.

Sunday, July 15, 2018

Finding Watch Rate

For celestial navigation we need to know UTC, formerly called GMT. We have many ways to get accurate UTC on land with internet connections. Offshore we need either an HF radio or satphone or we need to have a watch whose rate we know.  All watches gain or lose time at some rate. A chronometer is a watch whose rate (gaining or losing) is constant. The cheapest quartz watch has a rate of a few seconds every 10 days, and it is constant, which qualifies it as a "chronometer." A very expensive quartz watch might half that rate.

In another note and video we show various ways to get accurate time and demonstrate that these various sources do indeed give the same time, which took some coordination of sources. That article includes a 2015 rate measurement of a Timex quartz watch, done in a way similar to what is described here.

For now we illustrate the process of measuring the rate of a watch, in part to support our GPS Backup Kit that includes a rated watch. This shows the method we use to rate the watches we include in those kits. Chances are, some users of that kit will have their own quartz watch, which is probably more sophisticated (and expensive!) than the one we include. However, it is also just as likely that the watch in hand does not have a known rate. It is likely right to the nearest minute, but for cel nav we need to know UTC accurate to the second. Ask yourself now how much you would bet that the watch on your arm—or a crew member's arm—is accurate to the second, or that its rate is known the the correction can be computed.

On the other hand, these days it is actually not as likely that someone is wearing a watch as it was 10 years ago. Many folks have replaced watches with cellphone time, which is accurate when connected to a network. However, once we head off to sea, it is prudent to go back to wearing a traditional watch, preferably with known rate.

We start by setting all the watches to the same time, in this case, within ± 0.5s. The standard source for UTC used here is an iWatch connected to a cellphone network. We have confirmed that the watch is indeed ticking off the correct UTC seconds—although we did notice that every once in a while it appeared to hesitate a fraction of a second at the transition, but this did not affect its transition for the following second. Note iOS products default to using network time, but many Android phones do not, so you have to turn that on in settings, else the phone could be off by quite a lot.

So with a wireless connection to your phone, it will likely be the most convenient source of accurate time. Or your computer time when linked to the internet.  Computers and watches off shore away from any wireless connection, however, are essentially just stand alone watches, although in principle they should have a clock circuit in them that would be as good as a random quartz watch.

Off shore—or on land, for that matter—the primary source of accurate UTC is a GPS signal, which includes UTC as well as your position.  GPS is the source the phone and internet companies rely on to provide us with accurate time on our devices.

We are effectively using the GPS here to rate a watch in preparation for losing the GPS.  That is, we are talking here about rating a watch so we can do accurate celestial navigation, which would typically mean that for some reason we have lost all GPS navigation.

Below shows the watches lined up on Day 1 when they were set. The iWatch is on ZD = +7, so it was on day July 6, while the others are set to UTC, which would be 7 hr later on July 7.

The three Casios are model F-91W, which is perhaps the most famous of all watches. It is at least very popular.  Dating from 1991, they are still popular and sell for $10 (Walmart or Amazon), with millions having been sold globally. They are water resistant, with a 7-year battery.  The only weakness is this type of resin band, which if worn daily will only last a year or so before they harden and break. It is easy to replace the band with a more durable style. Also the light in them is not very useful; but they are accurate watches, known to last for many years.  The other is a Timex Expedition with several ocean crossings to its credit. Essentially this same model is available today for about $32. Its virtues are a super good light (Indiglo, a timex innovation) and true waterproof. Two time zones are also standard, but not needed. They are, however, no more accurate than the F-91Ws, as is the case with most quartz watches.

Next we want to start a notebook to keep track of the data. (If you use spreadsheets, the notebook data can be later transferred to the computer as a good way to organize the data and maybe make a graph of the results.)  We do not need any special math for this exercise.  We find time differences, then then divide by some time period to get the rate in seconds per, say, 10 days. This can all be done perfectly well with a few written notes in your logbook.

Here is the second data point two days later.

So far we have not learned much, but this will take a couple weeks.  For best values it will take longer. Good timekeeping would call for us checking and recording its error to extend the rate measurement as long as we have accurate UTC available.

This check does not have to be done every day, but some regular check every 3 days or so will lead to a better evaluation—see, for example, the plot of watch error vs time given in the link above. It will also be clear, even on the second data point, that the seconds do not turn over on the watches (test case and reference time) simultaneously, so we are only ± 0.5s at this point.  A way to get around this is illustrated below.

After a while it won't matter much if you are off ± 0.5 sec on each reading, we can still get a good average value over an extended time. But if you care to home in on the rate more quickly, then one trick that is a good estimate of the fractions of a second is to take a series of rapid cell phone pics of the two time sources. In this case is would be a phone taking a series of pictures like the one above.  Then make a table as shown below, this one made on the 7th day. It shows the watch errors from 8 pics, each taken just as the iWatch changed seconds.

Remember we are after the correction we apply to the watch to get UTC, so a positive number means we add this to the watch time; negative, we subtract it.  In this example, in the second pic of watch B, it read 2 second below the iWatch standard, so it is a +2. Now we can summarize what we have to date.

The set time and the first data point did not use the average cel pic method, so they are not quite as accurate, but this will not matter in the end, as we shall see.

The time difference between first and latest times in decimal days (dT) is figured from the times converted to decimal days (d.dd), which can be adequately approximated as d.dd = d + h/24.  The "10d-rate" is latest watch error (WE) divided by time elapsed since setting (dT).

We don't have good rates yet, but we have learned a lot. First, these $10 Casio F-91W classic watches (A, B, C) are indeed very good. They are all gaining time (except maybe C, which is spot on after 7.8 days), but at a very low rate, and the Timex Expedition is losing time. So far it looks like -2.3 s/10 days, but it is too early to tell.

I will post this note now, and then update it every few days till we get convincing rates. We should know these pretty well in another week or so... but again, for best cel nav practice, this should be considered an ongoing process where you keep a record of the watch error and date, from which you can continually update the rate... or better put, home in on a more and more accurate rate.

If you are using your own phone to compare to a watch, then you would need a second phone to take the pics. Or hang the phone over a computer monitor and use pictures of that for the series, such as shown below.  That is in fact how we did it for the rating example in our Celestial Navigation textbook in Figure 11.5-2. Most computers have some option to show the time on the screen... again we have to assume you have internet connections and have the system clock set to update automatically.

I will return to this post every few days for a while to update the rates.  For those following it, you will then see how the accuracy of the rate improves with time—or better still, find a watch and rate it yourself as an exercise in practical cel nav.

But looking ahead, here is what we are after (using new timing numbers):

We want to know the rate of the navigation watch and the date we set it. Say it turns out to be +2.4 s every 10 days, and we set it to have no error on Aug 8.  Then on Dec 3 we want to know the watch error so we can find a correct UTC.

First we figure the number of days between Dec 3 and Aug 8. You can count this out, or use the day numbers from the back of the Nautical Almanac—yes, there is such a table there, probably originally for this very purpose, although there are quite a bit of data in the Almanac that was at one time used frequently that we don't use much these days.

Dec 3 (day 337) - Aug 8 (day 220) is 117 days. Then 117d x 2.4/10d = 28.1s.  We read the time from the watch and add 28 seconds to get the right watch time, then we add the zone description (ZD) of the watch to get UTC. The ZD might be, for example, ZD = +4h, corresponding to EDT.

Belt and suspenders.
We are wearing the watch (watch time, WT) we navigate by, and it is set to ZD = +4.  That, by definition, means UTC = WT + 4h, assuming no watch error (WE). But we know all watches gain or lose time at some rate. In this case we know the rate is +2.4s every 10 days, and we set the watch to the correct ZD+4 time on Aug 8.  It is now Dec 3.

We did a sun sight and the WT was 18:20:05.  So we add 28s (as noted above) to get 18:20:33 on Dec 3. Then we add 4h to get 22:20:33 as the correct UTC to use when we look up data in the Nautical Almanac.

The data tables below will be updated every few days, with comments on progress. The date of last entry is given in the table, which is effectively the update of this data.

We are now 18 days into the measurement and we pretty much know the rates... plus we have learned a few valuable things from this exercise so far.

The first is, if you want to home in on the rate within just 2 or 3 weeks, then the photo method is crucial.  We had to throw out the first two B and C data points that were not taken that way.  In other words, you can't be wrong by a large fraction of a second and hope to learn anything in a day or two when the rate is barely 1 second every 10 days. The photo method works fine to get this to the tenth.

Here is a review of that method.  We take 10 cel nav pics each time the base watch switches seconds, which means even trying that we are random over that second on the pics. Samples are below.


Then we look at each pic to read off how many seconds do we have to add or subtract to that watch reading to get the iWatch value... which is a tested accurate time.  From that we make a scratch paper list as shown below.

This is easy to average. For watch B, for example, it is (10*3 + 6)/10 = 3.6 which is added to the main table above.  Takes seconds to do the pics, maybe 5 min to read each and write them down, and another few minutes to add to the table. So the full process to do 7 watches is about 10 min, which only has to be done every 4 days or so about 5 times.

That is all the good news learned so far.

The bad news is, I forgot the iWatch and used my iPhone for the master for the first 7/14 measurement, and discovered that coincidentally for the time of the measurements the iPhone was off by 1 second.  This could be spotted after doing the above exercise and noting the data did not make sense. It was obvious something was wrong, and that was the issue. Later that day, we did it again with the iWatch after getting it, and that is the second 7/14 entry in the table. In the first one, I adjusted all the measurements by 1 second.

I had checked this iPhone for accurate time very many times over several years, and it was always spot on. So this was a rare observation. And, about one hour later, it was magically right back on the correct time to the second.  Nevertheless, this is an important observation in this game.

This is effectively the end of this article.  We will add new data in a week or so, but i am guessing we know the rates. We also bid farewell to Watch A, which is off today in one of our Backup Kits for a world cruise, standing by to help the skipper if called upon.  Here is a copy of the certificate that went with the watch.

This type of plot can be made when the data are put into a spreadsheet, and fitting it with a curve is a bit better than just using the first and last points, but the rate in this case are the same, 1.227 vs the 1.2 we are calling it.