Active Cap't and Trusting your Sources

[Alaskan Sea-Duction]

Very good article.

Knowing and Trusting Your Sources – Slowboat

[Comodave]

Interesting article. Wonder if Garmin will check it out or not.

[tiltrider1]

Some very valuable Information.

[Jimboz]

Originally Posted by Comodave

Interesting article. Wonder if Garmin will check it out or not.

They should, as the new owner a copyright infringement lawsuit could be headed their way.

[healhustler]

Reading something like this just makes me want to throw up. Even in the few college essays that I may have come close to plagiarizing something or somebody, I hope I produced a more creative copy than that.

[BandB]

"Kayley" was one of the many areas of contention here with Jeffrey as even when pointed out, he'd do nothing, which made everyone believe he was Kayley. Either way, plagiarized.

As to the more important point of the article, as Mulder said, "Trust No One." Best to have multiple sources and not one copied from the other. However, even then you don't know when or by whom it was marked and you have to couple the information with what you see.

We always pay attention to any hazards shown on any charts or books we use. However, we don't assume they're right where placed and we don't assume because none are shown, that means none exist. Many times we've contacted a tow captain to get local information and been told about the shoal or hazard that wasn't as shown or wasn't shown, things too like the Port 30' of the channel has filled in from recent rains and is now less than 4' deep.

[Portage_Bay]

The authors of the article are spot on with their distinction between primary and derived source. But it's deeper than that. The serious student can start by Googling "Marine Charts Zone of Confidence".

[dhays]

As BandB alluded, the discussion on TF with Jeffrey regarding Kayley was very enlightening. It was a few years ago if I recall.

Portage, I wasn’t familiar with the concept of ZOC until I took your suggestion to Google it. Thanks.

One of the things that I appreciate with paper charts (Luddite that I am) is being able to see what survey the charts were based on. It is surprising how old some of those surveys are.

I readily admit to falling into the trap of confusing precision with accuracy at times. The precision of our chart plotters and GPS can fool us into thinking that the charts are as accurate as they are precise.

Another advantage of paper chart navigation for is that I don’t fool myself into thinking that I know precisely where I am with respect that rock on the chart.

[ranger58sb]

Originally Posted by dhays

One of the things that I appreciate with paper charts (Luddite that I am) is being able to see what survey the charts were based on. It is surprising how old some of those surveys are.

Another advantage of paper chart navigation for is that I don’t fool myself into thinking that I know precisely where I am with respect that rock on the chart.

And "paper" doesn't have to be actual, physical paper.

NOAA (for example) raster charts displayed on a plotter or in an app offer many of (most of? all of?) the advantages of physical paper, without some of the disadvantages.

-Chris

[Portage_Bay]

Originally Posted by dhays

As BandB alluded, the discussion on TF with Jeffrey regarding Kayley was very enlightening. It was a few years ago if I recall.

Portage, I wasn’t familiar with the concept of ZOC until I took your suggestion to Google it. Thanks.

One of the things that I appreciate with paper charts (Luddite that I am) is being able to see what survey the charts were based on. It is surprising how old some of those surveys are.

I readily admit to falling into the trap of confusing precision with accuracy at times. The precision of our chart plotters and GPS can fool us into thinking that the charts are as accurate as they are precise.

Another advantage of paper chart navigation for is that I don’t fool myself into thinking that I know precisely where I am with respect that rock on the chart.

Exactly! I wish the raster charts on a plotter made it easier to find notes, survey dates etc.

In general, the older the survey and less traveled by heavy traffic an area is the less faith I put in the GPS + chart plotter being accurate.

I can't find it this morning but somewhere I have a screen dump from Rose Point's Coastal Explorer displaying a raster chart, a pic of the radar and pic out the wheel house windows as I ran a narrow pass between a small island and the main peninsula. Radar and eyeballs showed me right down the middle. Plotter showed me on land.

[twistedtree]

Whether it's guide book info, charts, or your location, it's always wise to "triangulate" when navigating. The term of course comes from navigation, sighting the bearing to three different objects, and plotting those on a chart. The three lines should intersect at your location, more or less. The more precisely the lines intersect, the more accurate you location. And if the lines don't more or less intersect, then something is wrong.


The same idea can (and should) be applied to chart accuracy, guide book info, etc. Try to triangulate on an answer, and if the pieces of info don't agree, stop and figure out why. And definitely don't just rely one a single piece of info, especially for something critical.


The previous example of using radar, visual, and a GPS location on a chart to triangulate position is a great illustration. Three different sources are used, and in theory all three should agree. But one source was an outlier, so judgement needed to be applied. In this case your eyes are the most reliable, followed closely by the radar. And charts are know to be miss-located, so the chart was the data point that got rejected in favor of the other two that agreed with each other. A fourth data point was probably implicitly at play as well, namely water depth, which I expect corroborated the visual and radar locations, and further discredited the chart's geo-location.

[slipkid]

Good article. I always take what I read on active captain with a grain of salt and I'll confess I try to decipher if the info is from the sailing crowd or the powerboat crowd. I tend to trust one more than the other.

[BandB]

Originally Posted by slipkid

Good article. I always take what I read on active captain with a grain of salt and I'll confess I try to decipher if the info is from the sailing crowd or the powerboat crowd. I tend to trust one more than the other.

Wifey B: That's like reviews there. I look at the detail, not the averages. Sometimes the negatives are things I don't care about. Other times the positives are. Then those who grade because of price. Well, price is just fact, not something to grade on. If you stopped you already knew the price.

[nwboater]

Active Captain seems to be mostly an east coast thing. Never heard anyone refer to it where we cruise in PNW. After reading the article by Slowboat and its recent acquisition by commercial interests, probably best to avoid the habit (same with Yelp and other user review sources).

[BandB]

Originally Posted by nwboater

Active Captain seems to be mostly an east coast thing. Never heard anyone refer to it where we cruise in PNW. After reading the article by Slowboat and its recent acquisition by commercial interests, probably best to avoid the habit (same with Yelp and other user review sources).

We found it useful in the PNW and Alaska. We've found it helpful all down the coast and around through the Panama Canal, in both the Eastern and Western Caribbean, Gulf Coast, East Coast, US and Canada. I believe anchorages have more information and reviews along the East Coast, but we found excellent information on Marinas, bridges, and locks.

[JDCAVE]

There are several issues raised in this article. They note the “error” in the NOAA charts but don’t comment on the reason for that error. Further they incorrectly state that this error is “propagated” to Navionics and Garmin charts. The correct term is “replicated”. Propagation error refers to an incorrect fix(s) being propagated to the rest of the bearings used to create the chart. So...the entire inlet is incorrectly shown on the chart. This error may occur on locations that were surveyed before GPS became available and subsequently drawn on charts.

The whole “Active Captain” issue is...well...another issue entirely.

Jim

[tfmkevin]

Originally Posted by JDCAVE

There are several issues raised in this article. They note the “error” in the NOAA charts but don’t comment on the reason for that error. Further they incorrectly state that this error is “propagated” to Navionics and Garmin charts. The correct term is “replicated”. Propagation error refers to an incorrect fix(s) being propagated to the rest of the bearings used to create the chart. So...the entire inlet is incorrectly shown on the chart. This error may occur on locations that were surveyed before GPS became available and subsequently drawn on charts.

The whole “Active Captain” issue is...well...another issue entirely.

Jim

Hi Jim,

I think the use of "propogated" versus "replicated" is a nit in this situation, but I'll bite anyway. The error was not replicated. The error in the derived vector charts is different from, but caused by the origInal raster chart error. It is not a replica.

Since people like Garmin and Navionics are creating vector charts using raster charts as a source, they don't "replicate" anything. They are creating a derived version of the original.

Propogation doesn't denote what type of error is being moved from source to destination (unless there is some specific cartography usage of which I'm unaware - let me know if there is). It simply connotes the movement of something from a source to a destination. My intent using that word was to indicate that the NOAA chart error caused the errors in the others, but was not the same.

Webster's:

propagated; propagating
transitive verb
1 : to cause to continue or increase by sexual or asexual reproduction
2 : to pass along to offspring
3 a : to cause to spread out and affect a greater number or greater area : extend
b : to foster growing knowledge of, familiarity with, or acceptance of (something, such as an idea or belief) : publicize
c : to transmit (something, such as sound or light) through a medium

Also, you say that we didn't state the reason for the error in the original chart. We don't know that reason. When a NOAA chart has wrong information, we aren't aware of any mechanism to find out why the mistake was made. It simply happened - the chart doesn't reflect reality.

[tiltrider1]

Originally Posted by BandB

We found it useful in the PNW and Alaska. We've found it helpful all down the coast and around through the Panama Canal, in both the Eastern and Western Caribbean, Gulf Coast, East Coast, US and Canada. I believe anchorages have more information and reviews along the East Coast, but we found excellent information on Marinas, bridges, and locks.

BandB, I am not picking an argument. More like i’m Wondering if I know how to use active captain. I feel like nwboater. I get more info off my raymarine/gold navionics charts than ActiveCaptain. I’ve tried using the website and SeaIQ.

[tiltrider1]

Ok, just figured out what I was doing wrong with SeaIQ. Now I see the reviews. still can’t figure out how to use their web site.

[CaptTom]

I'm not a PNW guy, but I do know that Active Captain was initially populated with a lot of data which seemed like it came right out of the Coast Pilot and other print sources.

So both points may be true; there IS useful data for the PNW in AC. But for all I know there may not be as many user-generated entries like anchorages.

The good navigator uses ALL the information at their disposal, never over-relying on one source or disregarding another just because it's new or unfamiliar.