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Old 11-04-2019, 08:51 PM   #1
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Navionics sonar charts in SE Alaska

Has anyone used these? Is there much coverage and are they any good?

In some more frequently travelled areas these are pretty useful, and would be quite useful up there where some of the most recent surveys are 100+ years old.
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Old 11-04-2019, 09:35 PM   #2
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After reading your post.......I don't know. Sounds iffy.

I use electronic charts and guides to B.C. and SE Alaska....
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Old 11-04-2019, 09:46 PM   #3
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Problem of course is that the electronic charts are based on the same surveys, which are wildly inaccurate in some areas. I found areas where Navionics charts said 150 ft, CHS charts said 75 ft, depth sounder said 35 ft. These days, crowd sourced surveys can produce far more accurate bathymetry, but it requires many people traversing the bottom in question and uploading the data. Navionics then aggregates that into contours. Further south this has happened in a number of areas - just wondering what the coverage is in SE Alaska.

You'd want to be careful with it - when you punch up that overlay on your chartplotter you are warned not to use it for navigation. But some of the official charts aren't all that useful for navigation either.
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Old 11-04-2019, 10:09 PM   #4
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Im not sure about the Navionics information, but there are some recreational boats I know that are mapping with Garmin equipment up here, and the commercial guys have Nobeltec files with a lot of the area mapped in detail.
Are you already using the Navionics service for other areas? My understanding was you could look at what was available for up here if you were already a subscriber.
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Old 11-05-2019, 12:26 PM   #5
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I think you have to pay (substantially!!) to upgrade the card with the sonar chart information. If it's going to be empty, I'd rather save the money. That's why I ask. One clue is they have another feature called Sonar Shading which is useless to me but must come from the sonar bathymetric data. They recently added SE Alaska to the covered areas.

I used the structured sonar capability in this season's trip up there a fair amount, mainly to map ledges at the end of fjords to find an anchoring location. I'd not found it useful until then. Also when running very narrow passages, doesn't look ahead but you can see how close you are to the sides which gives you a clue.
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Old 11-05-2019, 01:35 PM   #6
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OK I think I answered my own question. You can download the mobile Navionics app and get a 15 day free trial of the subscribed information. The sonar chart coverage of the area is extensive, though not universal. It correctly depicts the narrow channel into Foggy Bay for example, but not the one into Culpepper Lagoon, shown at 1 ft deep which it is not. Interesting in that area, both sides of the narrow entrance have contours, but not the entrance itself. The shelf at the ends of some of the fjords are depicted, but the mudbars from the creeks not quite correct, change too fast I suppose.

It does certainly look useful. Not that you would depend on it with your eyes closed, but it would give you a much better idea where to look.
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