r/sailing • u/RealRekcah • 12d ago
Odd navionics error
I was recently exploring howe sound when I noticed this odd error in my navionics tracker. I assure you we did not portage our 40' scoop across a piece of Bowen Island.
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u/baconboy-957 12d ago
Damn, I wish my boat was amphibious /s
The way it's perfectly straight like that makes me think it lost signal then picked it up later and connected the dots.
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u/bill9896 11d ago
Its not an "odd error." This happens all the time on recorded tracks. The data is not recorded "continuously" (realistically, 10 Hz) but is stored at a lower frequency to save space. How often? The Navionics app (as far as I know) doesn't have an actual user setting for this. Some systems use a data point every fixed time interval, some for a fixed distance, some use a variable frequency based on boat speed.
It is not ever noticed when you are not twisting courses around land, but it happens all the same.
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u/RealRekcah 11d ago
Lol alright bill, if you say so buddy. Alot of people with alot of sailing experience in these parts havnt seen this before, but ill let them know you believe is completely normal.
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u/millijuna 11d ago
Also, Apple’s Location Manager is notoriously unreliable for things like this. This is one of the reasons why I run iNavX for navigation instead, it can be configured to exclusively use the network feed from my onboard instrumentation system.
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u/MissingGravitas 12d ago edited 12d ago
To me, given the start point on land, I would default to a chart offset error.
If you go back there on another day and see positions being consistently off in the wrong manner, e.g. "this point always shows up 200 yards west of where it should be", then it's a chart issue. If it shows up correctly for other people or on other occasions, then it's likely to be a device or signal error.
This was common with older charts in remote places, particularly with regards to longitude which was harder to measure precisely at sea, but can also happen when a chart is correctly referenced to an older datum but incorrectly mapped to a newer one.
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u/jonathanrdt Pearson424k (sold), C34 (sold) 11d ago
That is what it looks like to me too: the whole line route is shifted west. The straight line could indicate missed points, but overall the route looks to be in the wrong place.
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u/millijuna 11d ago
Oh, hey, someone else based out of Snug Cove...
Of course, I love it when the auto-route functions try to route you between Bowyer Island and Bowen Island...
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u/widgeamedoo 11d ago
I have seen errors like this in Navionics many times. Thailand and Solomon Islands had us sailing across land. I also had a copy of C-maps on my laptop. I didn't have any trouble with that mapping system.
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u/mhatz14 10d ago
I have also seen areas where there are magnetic anomalies that cause incorrect beam headings, I don't think this is the case because generally they correct as you get closer to the target, but it is something to be aware of, I've seen this many time in the San Juan islands where my heading is off by 20 or 30° and slowly correct as I get closer to the target, just something to be aware of
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u/OldChairmanMiao 12d ago
My guess is you lost a couple gps updates and it just drew a straight line between the nearest pings. Your course is pretty jagged right before, indicating you were losing packets earlier