Thursday, May 5, 2016

Is the Moon Waning or Waxing?

Periodically I read through one of our online course discussion forums, which has been accumulating over the past 15 years—sort of like skimming through a dictionary— and very often I run across extended notes buried on a special topic there that have long been forgotten, but deserving of some fresh air. This is an example, namely the question came up in cel nav course about deciding if the moon is waning or waxing.

So that of course first got the standard cel nav treatment, but following that were the parts that were a bit more interesting.  

Here is a copy of that forum post from 2004:

We are back from our Alaska training cruise (will write about it later), and on watch till we leave for the Pacific Cup Yacht Race on June 28. Then again off watch for 2 weeks.

Moon phases, appearances, and terminology issues are always puzzlers. There are definitely some things that change with location, but most are the same.

It is likely more an issue of which way are you looking to see the moon, rather than which hemisphere you are in at the time. At 2° N with a moon dec of 25° N, for example, i am looking north to the moon at mer pass, rather than the more common view south to mer pass from the NH.

Things that are the same:

(1) the words "waning" and "waxing" have their same English word meanings always, everywhere. Waning getting smaller, waxing getting bigger.

(2) the moon is waxing when it is moving away from the sun and waning when moving toward it. This is the key point and also one that is not so easy to picture... without a picture.

(3) the moon is full when it is precisely on the opposite side of the earth from the sun (GHA sun - GHA moon = ±180°), and there is no moon or a "new moon" when the sun and moon are on the same side (GHAs are equal).

(4) the moon moves eastward through the stars at about 12° per day (360°/30 days). This is true always, everywhere. If you see the moon next to Aldebaran bearing 190 M at 10 pm, for example on one day, then the next day at 10 pm you will see Aldebaran at roughly 191 M (sun moves 360°/365 days) and the moon will be 191-12 = 179 M. 



From Emergency Navigation

[These bearings are approximations since it is really the great circle arcs across the sky that are about 1° and 12°, not strictly their bearings on the horizon, but if their peak heights at mer pass are less than about 45°, this is a usable approximation—a point covered in some detail in the Emergency Navigation book.]

(5) the side of the moon that is lit up is the side nearest the sun. If you draw a line connecting the "two horns" of the moon — or equivalent points for other phases — and then draw a line perpendicular to that, you have a line pointing toward the location of the sun.







From Emergency Navigation


The above (5) statements are always true from any location, any time. And from these we should be able to answer all questions about moon phases.

Things that are different:

(1) When looking south to a body's daily motion, we see it's east-to-west motion as being from our left to our right, whereas looking north to view the east-to-west motion we see it moving from our right to our left.

(2) The shape of a crescent moon changes from "C" to "D," or vice versa, when looking to the north versus the south to see the moon. This is consistent with all of the above, but when it comes to making up rules on what the moon is doing (waxing- or waning-wise) based on what we see, such as the note below on whether or not the moon is "telling the truth,"  then we must qualify these with which way we are looking to see the moon, which in turn is often over simplified to specifying what hemisphere we are in.


"The Moon is always lying"

...in the Northern Hemisphere

There is a French saying that "The moon is a liar" (La lune est menteuse), which can be used to determine if the moon is waxing or waning. I have known of this for some years but never knew what it meant, nor how to apply it. Recently a student mentioned in passing that it must mean that the shape of the moon is a letter and the letter tells us what it is doing, but it tells us wrong! 

Well, indeed, it is as simple as that. "Croître" means "to wax" and "Décroître" means "to wane," as shown in the figure. When the moon shows us a "C" (croître, waxing) it is lying, it is not waxing but waning, and vice versa when it shows us a "D" it is not décroître but croître.
 
Don't believe me; I am lying.


—Thanks to Capt. Jean Faubert for filling in the details on this saying, and confirming that many French-speaking navigators have indeed learned it this way.


Celtic Goddess Symbol

When I explained this discovery to my teenage daughter [actually not a teenager any longer as I re-post this today], who I thought might be interested since she studies French, she said, "Fine, but isn't it simpler to just recall the Celtic Goddess symbol?," which she immediately sketched and explained: the waxing moon on the left represents maiden; the full moon in the middle, mother; and the waning moon on the right, crone. The symbol is unforgettable, and I had to agree with her. Thanks Britt. 






Wednesday, April 13, 2016

Connecting a Mintaka Duo Barometer to Expedition

There is much virtue in having an accurate barometer integrated into our echart programs. This can be accomplished with just an accurate sensor without displays of its own, or we can interface a full function device like the Mintaka Duo as well. Atmospheric pressure and its trend remains our key indicators of wind and weather changes, so having this displayed prominently at all times as we navigate or carry out route selection is always helpful. We typically rely on numerical forecasts that start with our present or recent positions, so seeing the true pressure we measured with an accurate barometer compared to the predicted pressures is a fundamental check on the forecasts… rather like comparing the depth sounder to the chart and tide tables as we enter shallow waters. 

Programs like Expedition add to the interpretation of what we see because they offer versatile graphic displays. The Mintaka Duo has its own app for versatile display and analysis but the convenience of comparing graphic plots of pressure with wind speed and direction is another bonus that program offers.

Connecting the Duo to a computer takes place in two steps, first prepare the Duo to output a NMEA sentence the program can read, and then configuring the program to read that input. This is essentially the same process for any barometer capable of this interfacing. These two steps are outlined below, illustrated by a video to show the steps in process.

Set up the Duo to export the NMEA sentences

Note that this only has to be done once.  Once the sentences are being output, it will continue to do so till you tell it to stop. It does not matter if it is removed from power; it will continue to out put the sentences when powered back up.

1. Download and install the Mintaka Commander App  from the “Connect your Duo to a Computer” link at www.starpath.com/duo.  There is a PC and a Mac version. Follow instructions there to insure that you have the USB drivers installed (also available at that link).  PC computers may  need to update their Java utility as well. Again, links are provided.  If needed the drives and Java update should just take a couple minutes.

Note there is no installer for either version.  You are downloading the actual app or exe, which you can put where you like and then just execute  it by clicking it. You may want to make a short cut, or move the app to your desktop.

2. Plug the Duo's USB cable into computer and launch Mintaka Commander App

3. On a PC, select the COM port that has been assigned to the USB port you are plugged into.  On a Mac you will see the serial number of your device.  (After you have run the app once, the data from the unit will be stored on your computer so you can return and look at the data off line if desired.  (If the COM port is uncertain, then open Device Manager and unplug and replug the device to see which port number shows up in the list of Ports. You might also see there the one being used for GPS and maybe one for Sat Phone, or maybe others.)

4. Wait for the databases to sync with the computer.  This takes a minute or two the first time it is connected; later connections this will be quick. Each pressure has a unique UTC stored with it along with other data, which are organized according to time intervals steps. There are up to 10 files like this to be synced.

5. Once synced and the graph is fully plotted, you have a couple ways to proceed. From the menu bar you can select Commands/ Run a command and type h and enter to get a list of commands, and there you learn that the one we want is AS which stands for Auto Sample. The actual command takes the form AS 5 XDR, which means send out the XDR sentence every 5 seconds.  If you just do AS 5 you will get out both XDR and MDA. ECS programs will want one or the other.  The NWS VOS ships using Turbowin will use AS 5 TURBOWIN   You can use any time interval in seconds that you choose.

6. So one option is just enter the command that way and it will start sending out the signals, but you will not know it.

7. The other option is to actually connect via the Terminal mode: main menu / Terminal / Connect.  Then in the status window below (where the cursor will be blinking) type AS 5 XDR and enter.  And then you will actually see what is being put out from the USB port. 

This will look something like

       $WIXDR,P,1.00678,B,BARO,*56
       $WIXDR,P,1.00677,B,BARO,*59

where you will get one line every 5 seconds.

8. Then disconnect the Terminal:  menu / Terminal / Disconnect, and you are done.

9. Close Mintaka Commander.  Note this must be closed before we can connect to the ECS because only one device can be connected at a time.

The Mintaka Commander App offers many valuable interactions with the Duo, which are explained in the Starpath help file and online at starpath.com/duo

If you should want to stop the auto sampling, connect to the app and run the command ASQ.

 Video illustrating the steps listed above.



Configure Expedition to display pressure in a Number Box and Stripchart.

1. Launch Expedition

2. On the top LEFT of the menubar, Click "Expedition" drop-down

3. Select:  Instruments / Serial and Network Ports

4. The COM port used in the Mintaka app should show up on the left. Select that one. (If it does not, be sure the Mintaka app is closed. Then try again.)

5. Set these Connection Settings: NMEA 0183 Instruments; 57600 Baud rate; 8 bits; None Parity; 1 Stop bits; Boat 0 Boat (0 def)
(Note the default baud rate of the Mintaka is 57600, but if there should be any reason for it, you can change this with a command in the Mintaka app.)

6. Leave unchecked: Redirect incoming data and Command.  Leave checked: Use position fix; Validate checksums

7. Then click Apply and then click RAW DATA button and wait up to 5 seconds for data stream to show (The send frequency of 5 seconds was set above in the Mintaka app.)  After data confirmation, close all set-up windows.

8. On the top LEFT of the menubar, Click "Expedition" drop-down, once again.

9. Select: Settings / Channels and set  Barometer “Damping (seconds)” to 0 on the left, and Barometer “Display precision” = 2 on the right.

Now we need to set up a Number Box to display the  barometric pressure "Baro" as follows:

10. On the top RIGHT of the menubar, Click "Window" drop-down and check or confirm "Number boxes" is checked. You can use any of the three boxes to show the baro data. You can display more than just Baro in one of the boxes.  

11. Click anywhere in the Number box window to display the "Edit" number boxes button, add Barometer, and configure the box to taste (i.e., Bold and with yellow background). Click the small + next to Barometer in the left panel to open the display options.  That baro display will then be persistent till you change it. It should be reading the same pressure you see on the Mintaka Duo, except Expedition will now be showing two decimals, whereas the Duo itself shows only one on the front display.

12. Launch Stripchart by clicking "Expedition" drop-down (top LEFT of the menubar), then “Applications" / "Stripchart"

13. At this point you can either add the baro to a chart layout already in use or if this is the first one you will see Bsp (boat speed) as  the default.

14. To add baro to an existing chart, click "View" / "Number of channels" and increment the number by one to add a new data strip.  It will be added as "Bsp" by default at the bottom of screen.

15, Right-click "Bsp" and click "Edit this stripchart" to access Settings and choose "Baro".  Click OK and the pressure feed will begin tracing across the stripchart.

16. Do menu Save to save the new baro strip chart template (This step saves the template, but not related to saving the data).  The video below shows a few ways to use the chart for reading pressure and tendency, including:
— use of tool tip
— note middle pressure shown is not a scale element, it is actual pressure at the moment.
— use of grid option
— use of wands and computed sd for storm warning in the tropics.
— recalling past chart data from the log file.


Video illustration of the points above.

______________________
A special thanks to Andrew Haliburton for itemizing the steps of this process, which was the starting point for the lists above.







Monday, March 14, 2016

Right of Way in the Traffic Lanes

In a recent article on how to know if you are in the lanes or not, we received a question (below) in the comments that has come up before. We answered there, but expand a bit here with actual links.

"Rule 10 (j). A vessel of less than 20 meters in length or a sailing vessel shall not impede the safe passage of a power-driven vessel following a traffic lane."

Does this rule apply to ANY "power-driven vessel following a traffic lane", or just to power-driven vessels >20 meters which are using the shipping lane?

Asked another way, if two boats each < 20 meters are in the shipping lanes, one is following the edge of the lane motoring north, and another crossing over the lane heading west (on the stb. side of the boat heading north), which rule applies? (Rule 10j or "boat to stb"?)

Finally, same boat <20 meters, motoring north following the traffic lane, but with a boat also < 20 meters under sail crossing the lane (heading east, and to the port side of the boat motoring). Which rule applies? (Rule 10j or sail over motor?)

There seems to be a lot of confusion about this situation in the Sound.
There are two key references that answer your questions. First is the full set of Nav Rules, and we have a super convenient document online called Starpath Pocket Nav Rules Handbook.  You can use it for quick reference with all related documents in one place—in fact, they are all on one webpage. You can also save it to your phone.

The next key document is the Puget Sound VTS Users Manual, which very specifically addresses points raised in the questions. This is a very useful document for all Pacific Northwest boaters.



In Rule 10 (j) the statement “following a traffic lane” means a vessel in full participation in the VTS, which in practice are ships and tow boats, and other larger commercial vessels.  The key part of their full participation is their scheduled radio contact with the VTS center, along with actually following the lanes. These vessels are to be contrasted with vessels that just happen to be in the lanes at the moment, but later or earlier along their voyage they take other routes that do not follow the lanes.

The vessels you refer to are not "following the lanes," they just happen to be in them at the moment.

The User's Manual explains who is required to have full participation and who may participate and under what conditions they may do so when not required.

20m is not required;  >40m is.  In practice, recreational vessels are expected to participate passively, as defined in the manual. (I leave these terms undefined here to encourage reference to the Manual itself.)

The fact that the track of a vessel is parallel to the lane,  inside or outside of the actual lane boundaries, is not the key factor when interacting with a vessel clearly not required to follow the lanes with full participation.

First part answer:
“Does this rule apply to ANY "power-driven vessel following a traffic lane", or just to power-driven vessels >20 meters which are using the shipping lane? “

So the answer to that is NO,  and again using the lane is not the issue; it is participating in the VTS that matters,  which is here called following a lane.

Second part answer:

“Asked another way, if two boats each < 20 meters are in the shipping lanes, one is following the edge of the lane motoring north, and another crossing over the lane heading west (on the stb. side of the boat heading north), which rule applies? Rule 10(j) or 'boat to stb' ?”

Assuming neither are “following the lanes” as described, these are just two vessels interacting in open water that has lanes defined in them, in which case normal crossing rules or sail-power rules apply.

On the other hand, if there are indeed ships following the lanes in the near vicinity, then both of these vessels must not impede them.  Non-participating vessels are encouraged to use the inshore zones, not the lanes themselves, which would minimize such three vessel encounters.


Third part answer:
“Finally, same boat <20 meters, motoring north following the traffic lane, but with a boat also < 20 meters under sail crossing the lane (heading east, and to the port side of the boat motoring). Which rule applies? (Rule 10j or sail over motor?)”

Again, we have the same answer.  I can see there could be confusion about the wording, but I believe that once these points here are noted this should remove that confusion.

In other words, if you are not in full participation with the VTS, which in almost all cases, you would not be doing unless you are a vessel required to do so, you gain no special rights when sailing in the lanes, regardless of your course.  When you see other vessels not following the lanes in this sense, you interact as you would in open water, assuming there are no ships near by, as they then become, in the wording of  the Racing Rules (whether or not you are actually racing), obstacles to your course.

We are standing by for discussion if it might come up.


Saturday, March 12, 2016

How to Buy, Register, and Download Canadian Echarts

This note was originally about ENC type echarts alone, but it turned out that the process of buying, registering and downloading the echarts is the same for both ENC (vector) and RNC (raster) echarts, so I have changed the title of the note, but not the body of the text, which still reflects the original motivation for the article, which was ENC.

When it comes to the actual installation, however, these two chart types from Canada are quite different, because of an extra layer of encryption applied to the RNC.

Also looking ahead a bit, we see below that the process is a bit long, and has to be done in the right order, but once this part has been done and you have a username and password with CHS, subsequent registrations and downloads are very easy.  The RNC install, however, is another issue and we will have to come back to that later. The ENC install is very simple.

* * *

In an earlier note on the Naming and Boundaries of ENC eCharts, I discussed the unique situation of needing one specific Canadian ENC if we wished to use all ENC in the Eastern Strait of Juan de Fuca, as might be the case, for example, when using Expedition for the Swiftsure or Victoria to Maui Yacht Race. This note is a follow up on that one.

In process of working with individual copy protected Canadian ENC, we learn quickly how lucky we are in the US with free echarts and super convenient access. It is all doable, but frankly tedious, and indeed there is no help online nor available from their telephone tech support. The phone support can help with BSB raster charts, but not the ENC, though I suspect now that the process is in fact identical for Canadian ENC and RNC.

This process is outlined in detail below, because the right path is not obvious, and any wrong turn spins out into a dead end.

(1) Choose the chart you want from the very useful CHS Interactive (graphic) Index (save the link, it is not so easy to find.)  The single chart at hand at the moment is CA470075, which they label with its paper chart name: V-3440 - Race Rocks to/à D'Arcy Island.

(2) Buy the chart. In principle there are numerous dealers of individual Canadian echarts, but the only one I found that could actually sell this is our friends at Captains Nautical Supply. In principle, this could all be done over the phone.

After you buy it you will get an email back from Captains with this information. The original prices are quoted at CHS in Canadian dollars as $25, which I assume this is as well.
Figure 1. Proof of purchase

Figure 2. Link to where you register and download.

(3) Register the chart, which takes place in several steps: we set up two accounts, download the chart, and install the chart.

Here are the steps, with apologies again for what seems maybe over explained, but one wrong step and it breaks. We start with the link provided by CHS when we purchased the chart  (https://register.chs-shc.gc.ca), which actually takes you to a different link:  https://inter-j01.dfo-mpo.gc.ca/registry-registre/.   We are getting early hints here that we have to stay sharp, ie there are two sets of instructions originally mailed to us that both go to the same link, which is not actually the link they go to.

We end up here:
(My original snag was I thought the blue fields were just table headers, but they are indeed the links.)
Figure 3
This takes us to Figure 4, and we then go direct to the bottom link. It is not clear what the top part is referring to. I think GC means Government of Canada.

Figure 4.





If you have already in the past registered, you can log in here, but if not we now start the process of setting up an account with the Sign Up link on the next page.

(If you later need to download a second copy, this is where you would log in to do that, and it would be straight forward. But you must then log in with the same account that you registered the chart with originally.)

Figure 5



Figure 6
Figure 7



NOTE  they have strict rules on names, hints, questions and answers. I have marked these in red boxes.

Figure 8

Figure 9
IMPORTANT NOTE. Be sure to save this information so you can regain your login if needed.

Figure 10


IMPORTANT NOTE: If you delay very long at any page you will get the following message when you hit Next or Continue. I am not sure how long you have, but it is not long. Maybe just 5 min or so.  If you get this at the end of the process, as I did once trying to record all of my answers etc, it is very discouraging. You get to start all over.


Figure 11


With no errors, the Figure 10 Continue button will take you to Figure 12 below.

Looking at that one, you will not have received a DFO passcode as so far we did not give any email address.  So in this window you will choose Self Registration. 


Figure 12


After choosing Self Registration, you get the screen below and now we can start the real registration.

Figure 13

Figure 14


Figure 15

NOTE in the form below (Figure 16) you must enter a Unit Type, even though it is not marked as required.

Figure 16

Figure 17

The next figure is a summary of your registration information with CHS. Print this or save it as a pdf, as you may need it to recover the chart or a login.  Maybe a call to them would get it, but not sure.

Figure 18

Then when you save this, you will be back to your products page, which will not have any,  and you can add them.

If you do not get sent back to the next page below, then just start over and on the first page (Figure 5 above) enter your Username and password selected earlier, and you will get here.  This is where you paste in the code for that chart that was mailed to you.


Figure 19
NOTE in the above we do not use the link License a Product.

After you add this product, the same page will then have it listed further down the page  under the section Active Products.



 And it is here where we download the chart.

IMPORTANT NOTE. It might take several clicks.  Click it once and wait a few seconds.  If nothing happens, try again. In one test I had to try 3 times, and this behavior has been confirmed to me by other users.  But be sure to give it 5 or 10 seconds between clicks.

Figure 21.

And then we get our chart, which you just save to your downloads folder.  This zipped file is then all standard ENC format.  It is easy sailing from here on. Again, if you need another copy for another computer, you can start from the beginning and just log in.

Figure 21



Below is a video on how to install this ENC into Coastal Explorer, along with related notes on using this program to select, download, and install US ENC.





Sunday, March 6, 2016

Naming and Boundary Conventions on ENC eCharts

In a recent article (The Strange World of Electronic Chart Boundaries)  I pointed out the unusual nature of the shapes and names of electronic navigation charts (ENC), which are the digitized vector versions of the raster navigation charts (RNC). The latter are echarts made from exact graphic copies of the paper charts, and in that sense their sizes, boundaries, names, and scales are immediately understandable to anyone familiar with the paper charts.  This is not at all the case when we move to the vector ENC charts.

There were several questions raised in that note that have taken more research. In short, that note just described the situation without providing any reasons for it. Since then I have made progress on understanding these ENC properties, thanks primarily to good support from NOAA's Office of Coast Survey (OCS), who do indeed care about the best use and understanding of their products.

There are two basic factors that lead to the unusual properties we end up with on the presentation of the ENC—I am not discussing the content of the charts at all here, just the issues of size, shape, boundaries, and scales.

First, the US ENC are made from the available RNC. That is, to make a vector chart of a region, step one is bring out the largest scale RNCs of the region, and then digitize these products in a standard ENC format. Digitizing means converting a curved shoreline or depth contour into a sequence of straight line segments and storing a data base of these points, which is then included in the ENC files we load. Then an echart program can draw the chart on the fly each time we change a display scale or move to a neighboring or overlapping ENC. It is a complex process to make these, but much of the data are already digitized and all new survey data comes in digitized as well.

Then at the location of each aid to navigation (ATON) the data describing it are entered into another data set included in each ENC. (Though probably not so well known, the header file components of RNC kap files include the precise Lat-Lon of each prominent aid as a georeference point of the RNC, which insures these are in the precisely right place to match the Light List and latest Local Notice to Mariners; recall RNC and ENC are updated as needed every week or so.) It is this step of the ENC production that could add much more ATON information than possible on an RNC, and often this is the case—but not always. In the case of rock symbols, for example, the ENC descriptions sometimes include less information that we can get from the rich set of RNC rock symbols described in Chart No. 1.
 

That is the way the ENC are produced, but they cannot be published in this direct one-to-one relationship between a new ENC and the long established RNC, which brings us to the second factor affecting the ENC boundaries we see.

The reason they cannot be the same is the International Hydrographic Office (IHO) has standards on these ENC echarts that all participating nations must follow, and the US is indeed a participating member [see References].  This situation has pros and cons. The main con is, the US does not have complete freedom to produce ENC in any scheme they might deem most logical based on our RNC system. The main pro is we end up with charts that match an international standard that better serves the thousands of foreign vessels that visit the US each year, and indeed then makes foreign ENC familiar to US mariners visiting their waters.

The primary IHO restriction that affects the boundaries and scales of US ENC is no ENC can overlap an adjacent one within the same scale band. That brings us to a key factor in understanding the boundaries of ENC, namely the concept of scale band or usage band.   The IHO defines 6 usage bands, and recommends the scale ranges that each of these bands should cover. The table below summarizes these as best I can tell.  These definitions are useful for selecting charts in catalogs and for understanding the names, and in turn the ENC boundaries we see  in navigation programs.




The US values do not coincide with the IHO values because the US had been making these ENC before the IHO made their recommendations. The British Admiralty ENC is  marked with a footnote [*] because although they do use the IHO values for their own ENC, they do not use the name Scale Band, but more often prefer Usage Band.  I think the reason for that is they have a vast worldwide chart distribution network (they distribute the charts made by other nations), and different nations have different definitions of the actual scales in each usage band as shown. The Canadian one is notably different.

The scale band is a key to understanding the names of all ENC. In the case of US products, the first digit after “US” is the scale band. Thus for the chart we discussed earlier, US5WA18M, the US means US product, and the 5 means this chart has a scale band 5 (i.e. between 1:5,000 and 1:50,000). The WA means the chart is either wholly within the state of WA or when covering overlapping states, the majority of the chart is in the state of WA.

Scale bands 3 to 6 are generally associated with a specific state. Bands 1 and 2 are often labeled:  EC (for East Coast), GC (for Gulf Coast), and WC (for West Coast), but there are some overlaps in these descriptors with the state descriptors.

We can think of the “M” as a reminder that the native units of these charts are metric (although we can display them in other units if we choose), or we can think of it as a filler since all ENC worldwide must be 8 characters long—
I would have to agree that dealing with an extra M is better than dealing with leading zeros.  

The fact that the actual sequence of numbers (i.e. the 18) do not always follow a logical sequence along a waterway is just a matter of history in the production sequence, much as the chart numbers of the RNC are not in any particularly logical order.  If anything, the ENC are more often in sequence than the RNC counterparts.

Thus we have this sequence of charts coming in from the ocean toward San Francisco:

US1WC01M (1:3,500,000)
US2WC12M  (1: 1,200,000)
US2WC06M (1: 811,980)
US2WC05M (1:868,003)
US3CA14M (1:207,840)
US5CA12M (1:40,000)
US5CA13M (1:20,000)

The first two (scale bands 1 and 2) can overlap as they are different scale bands, but none of the three band-2 charts can overlap.  Likewise the last two here (band 5) cannot overlap and will change charts at a specific line.  The NOAA Online Interactive Catalog is the best way to study this, short of having the built in convenient presentation of Rose Point navigation software, mentioned earlier.


Note too that the US ENC chart numbers are only unique within state designations and scale bands. Thus in our US5WA18M example, we can have a US4WA18M as well as a US5OR18M, but there are never two charts with the identical name.

In learning to use this system we might also keep in mind that the US ENC scale bands are not the same as historically been used in the US for paper charts. The US Chart Scale Classifications are defined in Chapter 1 of any US Coast Pilot and Bowditch as:





The IHO paper chart categories are also shown, in part to show these are broad categories with no definitive boundaries. In my own experience, I tend to think of 1:40,000 to 1:80,000 as "medium," being between "large" (less than 40k) and "small" (more than 80k).

It is not clear if this difference in scale range definitions between our traditional paper charts and modern ENC has any significance.  It certainly provides navigation schools and USCG exams nice ways to make trick questions, but probably not much more than that.  The standard US paper chart classifications never had, to my mind, much influence on practical navigation, but the new ENC scale band system does indeed have a meaning, i.e. it determines the third character in the name of any ENC, worldwide.  It could be that the upcoming new edition of Bowditch will address this matter.

So now we can go back to our example from the earlier article to see why the boundaries of the ENC equivalent to RNC 18474 (ie
US5WA18M) are what they are—again, the NOAA Online Interactive Catalog is the best way to follow along.  When NOAA sets out to cover the ENC charting of the region covered by 18474 (scale 1:40,000), they start out by digitizing the largest scale RNC charts that cover that region. In this case, the north half of this chart is covered by RNC 18449 at a scale 1:25,000. (The south half of 18474 does not have any larger scale over the bulk of those waters.) These are both scale band 5, so to meet IHO standards this chart must be broken up. They cannot overlap, so that breaks up the region into two parts 5WA14 and 5WA18. Then we notice that RNC 18449 also overlaps RNC 18450, which is scale 1:10,000, which is also scale band 5, so it cannot overlap and has to be separated out. Thus we are building up the irregular rectangular shape of the ENC.

The same thing takes place to the south with overlapping 18448 and 18453, both also in scale band 5.  Note that the Port Orchard and Gig Harbor charts, which are also in scale band 5, are not cut out because they lie wholly within their respective ENC cells. They do not “overlap,” meaning part in and part out. Individual ENC charts are often referred to as "cells."



 * * *

We are left then with just two points raised in the first article, namely the confusion that might arise from the ENCs internal description of the corresponding RNC given for each ENC. These will always correspond to the name of the RNC that has the largest overlap with the ENC that is of the same scale. There will not often be a close correspondence, and in fact this formula for the internal description of the ENC can often be notably wrong, as in the case of US4WA.

OCS is aware of the confusion this might cause in some cases, and they are considering solutions. It is a big project, however, to name these more precisely. In principle, an algorithm could be written to make these names more realistic.  For now the key point for mariners is to simply understand this limitation when reading the ENC descriptions that their echart programs reproduce. They are not making this up, this is what the ENC says it is. 


 * * *

The other issue is the area of missing US ENC in waterway between Victoria and Race Passage, covered by US RNC 18465 or Canadian RNC 3440.  This waterway is all Canadian waters, which must have contributed to the results at hand.  But we still have the unique situation that an American vessel could sail from an American ENC of Haro Strait’s Canadian waters toward Race Passage and onto another US ENC, but have to cover up to 23 nmi without any US ENC. 


Sample of the NOAA Onliine Interactive Chart Viewer

It is not unprecedented that US ENC cover Canadian waters, but in this case we are forced to use the Canadian ENC, because of another IHO requirement that no two Nations can make an ENC of the same waters within the same scale band.  This means the US had to cut out a section (now the missing part) of the US ENC equivalent of 18465 (called US4WA34M) and mariners must now use Canadian ENC called CA470075. This was a direct conflict of overlapping scale bands (note the 4 in each chart name) from two nations, both of which had previous ENC of this region. This particular cell is now covered exclusively by Canada as a direct result of negotiations between the US and Canada about how they were going to meet the IHO standards along all of their long and complex common borders. In short, this is a compromise in these negotiations.

This situation stands out because many commercial vessels, as well as some racing yachts, prefer to use the same source of ENC, which is not possible in this unique case. We need the Canadian ENC of these waters, CA470075.

Individual Canadian ENC were not available in the past, but as of a month or so, they are in principle for sale. This one has a price of CND$25. It can be seen on Canadian Hydrographic Service  Interactive Chart Index, which is good way to view all of their charts, print and electronic… but save that link. It is hard to find.


Sample of Canadian Online Interactive Chart Viewer
I have purchased this Canadian ENC from our friends at Captains Nautical Supply and have documented the registration process, which is not entirely obvious. There are also there several videos on how to install the chart of a couple echart programs.

I would like to make a special thanks to Steve Soherr of the Customer Affairs Branch at NOAA's Office of Coast Survey. He has helped me and many others with charting and related questions many times over the years. The above notes, however, are my interpretation of the resources, and any misunderstanding or misstatements are my fault alone.
 

References on IHO requirements and US-Canadian ENC negotiations

The key acronym at IHO for the topic at hand is WEND (worldwide electronic navigational chart database). 

WEND Principles (from IHO)
Facts about Electronic Charts (from the IHO)
S-57 Interactive Object and Attribute Catalog (www.s-57.com)  Takes some patience, but it is all there!

The US-Canada agreement on ENC
The specific case of Pacific NW waters.


As noted earlier, the ENC format is still a bit in flux, but not to worry. It will soon be replaced with a new standard and much of this might change.  See S-101 Product Specification for the Electronic Navigational Chart



Friday, February 26, 2016

The Strange World of Electronic Chart Boundaries

This note outlines the subject and the questions it raises.
Later articles linked at the end present some of the answers.

There are two kinds of electronic charts of US waters, both free downloads from NOAA. Raster Navigation Charts (RNC) and Electronic Navigation Charts (ENC). There is nothing strange about the RNC. They are graphic images of the latest paper chart of the same name, with the same boundaries. When first getting into electronic charting, the RNC style is most likely the best to start with. The charts look exactly like the ones we are used to.

The RNC do have the advantage over their paper parents of always being the latest edition, never older than about 10 days.  We might be reluctant to spend another $28 or so on a new printed chart every time there are new editions or corrections, but with the RNC we can just click a button (when online) and it will be automatically updated in our navigation programs—at least in full feature programs such as Rose Point's Coastal Explorer.

Eventually, however, we will want to broaden our charting interface to include the vector displays of the ENC. There are several reasons for that. In some cases, there are no RNC counterparts at the scale we want. Also, in principle the ENC can include much more information because they include multiple layers of data. Not all versions include anywhere near their full potential in that regard, but it is possible, and also in principle these just get better with time. The land outlines and ATON detail improve with each new version. They too are updated about every 10 days or so, but like the RNC they actually change much less frequently than that.

That is not to say there are not drawbacks to the ENC. Their treatment of rock symbols, for example,  is a giant step backwards, but even though some 10 years or more old by now, they are indeed still evolving—and in the words of NOAA, sometimes "a little rocky." Nevertheless, they were just last week or so, approved as meeting chart carriage requirements on some vessels.

From the latest edition of Chart No. 1.

Another feature of ENC that could be an advantage to some users, while at the same time considered a drawback to others, is each user can redesign the layout. Don't like the colors, just change them; want depth contours ever 4 fathoms instead of 10, just change them. Thus you can customize the look of the chart for special applications, whereas some users might consider that having invariant display standards is crucial to safe navigation when multiple navigators use the chart.

Beyond these pros and cons—subject for another article—there is a further call for ENC in that some tactical navigation programs whose main function is performance analysis and weather routing are often better run on the digital vector charts  (ENC or equivalent) rather than on the large image files of the RNC. In short, there are various reasons we might want to use the ENC.

And with that brief background, we come to the topic at hand.  The moment you decide to use the ENC for any reason, you discover a logistics issue that might not have been anticipated. Namely the chart numbering system defies any apparent logic, and the chart boundaries are irregular at best.

The examples given here are for Puget Sound, but the points being made apply to any US Waters.

Suppose you want to look at the ENC equivalent of 18474, Puget Sound–Shilshole Bay to Commencement Bay. You will find this chart on the NOAA Interactive Catalog, ENC section, and it is called US5WA18M, and it is indeed described as equivalent to 18474, Puget Sound–Shilshole Bay to Commencement Bay. The actual ENC situation, however, is illustrated below.

Figure 1. The ENC charts that cover the same waters as RNC 18474. Numbers in parentheses are what the ENC call the equivalent RNC.

We see that ENC chart US5WA18M (the green part alone in Figure 1) does not at all cover the same waterway. Furthermore, if you do want all the ENC charting that covers the waters of 18474 you will need 6 ENC charts. There must be some logic to the boundaries, but it is not obvious, nor predictable. Also, once these are all loaded into your program, it is only the US5WA18M that will describe itself (incorrectly) as "Puget Sound–Shilshole Bay to Commencement Bay."

Also the scales of adjacent charts do not match in the same way many RNC do. In RNC we often have a sequence of neighboring charts on the same scale, say 1:40,000 or even 1:25,000, but this is not the case with the ENC. The RNC of 18474 is 1:40,000. The ENCs that cover this chart area vary from 1:15,000 to 1:80,000.

With vector charts (ie ENC), however, the disruption going between adjacent charts of differing scales in a quilting display is not as often an issue as it can be in some RNC displays, so these scale differences are not a major issue, and indeed a virtue on some level.

Unlike RNC, there is much less likely to be any overlap between adjacent charts; they typically (not always) end right where the neighboring chart begins, but there can be ENC inserts, wholly within a smaller scale ENC chart.

But there can be other surprises,  as we see in this same type of comparison for RNC 18465, Eastern Strait of Juan de Fuca.

Figure 2. The ENC charts that cover the same waters as RNC 18465. Note there is no US ENC coverage just south of Victoria. Numbers in parentheses are what the ENC call the equivalent RNC.

This is a popular sailing area in the Pacific Northwest, and waters of several yacht races. Here we see that that the waters of RNC 18465 is spanned by 7 ENC segments. The irregular blue section is the one NOAA calls equivalent of 18465. This is quite a hodge-podge, but rather worse than that is the waters of Victoria Harbor leading out to Race Passage is not covered by any of the US ENC charts.  Simply knowing that fact can save much puzzlement when using ENCs in this region.

The way around these issues in a basic chart program such as OpenCPN is to be sure to load all the ENC over the broad region you are sailing in. Then most programs will quilt and load these as needed, without you having to figure out which ones you actually need based on the chart name they present, which, as noted above, will not be logical very often.

This too points out a good selling point to look for when shopping for an echart program, especially looking forward to using ENC. A full-feature program will actually let you download the charts from within the program itself. Rose Point's Coastal Explorer, for example, has an especially nice way to do this by presenting to you the same ENC outlines you see on the NOAA Interactive Catalog.  So you can just click the ones you want, see them highlighted to confirm their coverage, and then install.

We cover the use of all echart formats in our online course on coastal navigation with illustrations using both OpenCPN and Coastal Explorer.

The video below shows how each of these programs end up presenting us with the misleading descriptions of these ENC.




— A special thanks to Tobias Burch for a nice solution to the graphics challenge of this note.

* * *

UPDATE 3/6/16.
Answers to several of the questions raised above have now been posted here:
Naming and Boundary Conventions on ENC eCharts.



Sunday, February 21, 2016

Great Lakes Wind Forecasts from HRRR

There are new weather sources available as of a  month or so, that have a big impact on marine weather of US inland waters across the country. Namely the HRRR model forecasts in grib format that we have discussed recently for waters of the Pacific Northwest. These data are available nationwide, so I want to highlight a few other regions starting with the Great Lakes.

The Great Lakes already have excellent forecasting, but I think this new data will add to even that. More  experienced users in that part of the world may know of better sources, but it seems to me one of the best is from the Great Lakes Coastal Forecast System (GLCFS). Below we take what we can get at this moment from that source. The GLCFS uses a model that is initiated every 12h, which makes it similar to the one at UW we discussed earlier.

Here is what we get going there now. [A video at the end illustrates the links.]

The Latest forecast as of 0400z is 4h old; the next surface wind report will be at 0628z, but that one (called Nowcast) does not have forecasts. The next forecast will be available at 1330z, which would be their 12z initialization. Thus it looks like it takes them 1h 30m to process the data and publish it, which is pretty fast.

Looking to other forecasts, we can compare that one to the free HRRR data online, from which at the moment we can get:


This data is 2h old. In other words, even though the model is run every hour, it takes about 2h to  process and publish the results. This too is not bad. Global models take up to 3h for maps of the ocean.

The other option I want to highlight here is we can get this same HRRR data from the commercial service of ocens.com, which offers this data in grib format via their WeatherNet service. It costs about $3 to download 15h of wind and pressure over the Lakes region. An example is below where the data were loaded into Expedition. The Ocens grib files should load into most grib viewers or echart programs that display grib files.



This is the same data we viewed graphically above, so it is also 2h old, but viewed in grib format it is much more detailed. Furthermore,  we at hand this way the full 15h of forecast, as shown in the video. We have more detail and we can read wind and pressure digitally at any cursor location. This can be compared to the free online view of the HRRR and GLCFS graphic data shown above. 

For actual checks of the model accuracy, it seems there is one buoy right in the middle of the south end of the lake (Buoy 45007), but that one is not providing data at the moment, so we look to the Chicago area. This could be even more interesting region to look at as we see that this forecast calls for nominally 5 kts (±2.5) from the NW, which is notably different from farther offshore. Viewing the data in a grib viewer, we can read the actual forecast and do not have to rely on the definitions of these wind arrow symbols. We can find the actual wind in Chicago at 04z (turns out to be about now) from the NDBC site for this Chicago station CHII2, where we find that this particular forecast is more or less spot on.  By the way, there is a really neat webcam showing conditions in this area.

There is every reason to believe that this HRRR forecast is the best available for the Great Lakes. It could be GLCFS and other sources of NWS Great Lakes forecasts are using it now, but it does not seem so from the above. Furthermore, even if they do use it for their 00z and 12z runs, the beauty of the HRRR model is it is run every hour with full assimilation of all observations over the past hour. In that sense it has to be by default superior to others for practical use.

Eventually we might have other sources of this data in grib format that will be available publicly at no charge. For now we thank Ocens for pioneering this presentation, which should help mariners across the country. Ocens does offer a free 3-day trial period for WeatherNet that can be used to download the data. We have a video on how to do this, which is good to check out when you have just 3 days to try it.

The video below illustrates the links above with a bit more annotation.



Saturday, February 20, 2016

Introduction to AIS

The Automatic Identification System (AIS) is a worldwide electronic navigation system designed to prevent collisions and to facilitate maritime traffic control and security. It was developed for commercial vessels, but any vessel can take advantage of this important service on some level. It is now a key component of the electronic instrumentation of all vessels, recreational and commercial.

AIS shows where all ships and other commercial vessels within VHF radio range are located—they are required to have AIS—as well as all of the other vessels who have chosen to add optional AIS transmitters. AIS signals include the vessel’s dynamic data: Lat-Lon, COG-SOG, and true heading (requires a separate heading sensor), as well as certain static data such as name, MMSI (Maritime Mobile Service Identity), call sign, vessel type, length and breadth, and GPS antenna location. Signals from Class A broadcasts (discussed below) also include voyage data including destination, ETA, cargo, rate of turn, present draft, navigation status (moored, underway, restricted maneuverability, constrained by draft, etc).

You have two ways to take part: You can install a receiver alone to learn about traffic around you, or you can install a transceiver, to both see AIS traffic and broadcast your own AIS information as well. Both are optional for recreational mariners, but transceivers are mandatory for commercial traffic. Receivers alone cost $60-$300, whereas transceivers are in the $800 to $3,000 range. At minimum, an AIS receiver should be considered standard electronic navigation equipment on all recreational vessels. Reception alone is very easy to set up; some new VHF radios include AIS output as an option, sharing the same antenna. Transceiver set-up is required to be assisted by a certified technician.

There are a few simple, but important, basics: First, we need a way to display the targets. The higher end receivers include a display of text data—which is not so convenient if that is all you set up—but all receivers have an output in NMEA format. The simplest solution is input the NMEA signals to your electronic charting system (ECS). This might be some integrated package of instruments and displays, or without that, you can run echarts on a laptop. AIS receivers have a USB output that goes directly into your computer. The free OpenCPN program, for example, has many convenient AIS display options, as do all commercial echart programs.

Next, there are two classes of AIS signal transmission: Class-A transmission is the higher-end type required on ships and other commercial vessels, and Class-B transmission, available to vessels not required to carry Class A. All AIS receivers display both A and B signals, so the equipment decision is mostly receive only or transmit and receive. Recreational mariners can choose Class-A or Class-B transmission. Class A transceivers offer higher performance, but they cost more, so the Class-B transceivers are more popular with vessels not required to carry Class-A.

Vessels required to carry AIS Class A include: all commercial vessels over 65 ft, towing vessels over 26 ft with horsepower over 600, vessels certificated to carry more than 150 passengers, most dredging vessels, and all vessels with dangerous cargo.

Vessels required to carry AIS Class B if they do not carry Class A include: fishing industry vessels, and some passenger vessels that do not use traffic lanes nor have speeds over 14 kts. Vessels that would otherwise be required to carry AIS, but whose operations are restricted to a 1-nmi radius, can apply for an exemption to the AIS requirement. Other previous exemptions to the carriage rules all end on Mar 1, 2016. Vessels required to carry AIS must turn them on not later than 15 minutes before getting underway.

In short, ships, tow boats, and most larger commercial vessels use Class A, as do some fishing vessels, but most fishing vessels and most recreational vessels will be using Class B. Table 12.19-1 compares the specifications of Class A and Class B.

 

AIS can also be of great assistance in basic chart navigation in that prominent aids to navigation (buoys, lights, bridge pillar marks, etc) often send out AIS signals that show up on your echart display in the proper locations (labeled ATON). [I will add a note shortly on AIS ATON Symbols.]

Collision avoidance is also greatly enhanced by AIS because most echart programs read the AIS dynamic data of the targets and they know your own COG and SOG, so they can compute and display for you the closest point of approach (CPA) and the time to the CPA (TCPA) based on present conditions. Then as either of you alter course, you watch how this changes.

Search and rescue operations have special AIS modes that locate vessels and aircraft involved. There are even small, personal AIS transmitters that you can carry and activate if overboard so you show up on all local AIS receivers.

AIS reception also enhances your radar watch in the ways listed below.

AIS Synergy with Radar

1. AIS can find and communicate with targets hidden behind land or around corners that radar cannot see, and then plots them on an echart as if seen by conventional radar.

2. A radar echo can be identified or contacted by vessel name and vessel class rather than using a generic hail.

3. Target interactions (CPA, TCPA) can be improved because the target vessel is broadcasting performance data such COG and SOG and even a rate of turn when turning.

4. Extended tracking range is obtained since VHF communications reach out farther than typical radar ranges and thus passing arrangements can be made long before the vessels meet.

5. Ship target intentions will be more clear, and will help with maneuvering decisions, because the target’s destination, ETA, cargo, draft limitations, etc. are broadcast along with other AIS data.

6. Some ECS radar displays and all commercial vessel radars have an input for AIS signals so they can display the AIS targets overlaid on top of the radar targets.

There are numerous AIS sources online and in mobile apps that present near-live AIS signals for most waters of the world. In principle we could use our smartphone with a 4G connection to actually see the AIS targets around us when we are underway. This however, is not at all a dependable or safe approach. There is often a large delay between actual AIS reports and the ones we see in these apps, and this could lead to serious navigational errors.

A sample of AIS targets displayed in an echart program is in Figure 12.19-1, with a detailed view in Figure 12.19-2.
Figure 12.19-1. AIS targets viewed in OpenCPN. Active or selected target is the one whose information is being displayed (marked with a square box), else the targets are called sleeping targets, which is misleading—they are sleeping only in that you have not chosen to read the data. Echart programs often have ways to annotate or color the symbols beyond the standard format. Projected vector lines show COG and SOG. The above are set to show 3-minute projected positions. Sometimes we can detect current when the true heading line is different from the COG. Destination information when present is more often wrong than right. This has to be manually updated and often gets overlooked.


Figure 12.19-2. ECS display can be set to show actual target size and precise location when zoomed in. On the right is our vessel, also scaled to right dimensions and precise location.  We can see that the target heading and COG are different. This is viewed with OpenCPN.
__________________

These notes were adapted from our text Inland and Coastal Navigation, 2nd Ed. We will follow up with a report on several specific AIS receivers, including this neat unit that is made here in Ballard, a few blocks of Starpath HQ, called the dAISy. It is powered via the USB that connects it to your computer.


A dAISy with a ducky (not included). It does include an adapter to a standard antenna connector.

References (We are lucky here, there are excellent references online.)


USCG Nav Center AIS section.

Wiki on AIS.