Navionics - A Childrens Toy?

[Simi 60]

Originally Posted by carstenb

So If Navionics gets it this wrong on an old well-established harbor - what else is wrong?

Plenty
I was anchored in a spot a few days ago that navionics had as land.
We had 8ft of water under out 7ft draft.

Anybody have have nay suggestions? Or should I just chuck Navionics and buy C-Map

Dont chuck it but by all means get as many sources of information as possible and dont necessarily trust any until you have safely traversed that area yourself.

[Simi 60]

Originally Posted by Breaking Waves

curious - how do you know/get water depth from looking at a sat photo?
Can you tell accurately what the lowest depth is in this photo?

Attachment 208072

Thats not how you look at Sat images

[arsenelupiga]

Originally Posted by Breaking Waves

curious - how do you know/get water depth from looking at a sat photo?
Can you tell accurately what the lowest depth is in this photo?

Attachment 208072

Sorry duno what area is on the pic.

I crosscheck number of satelitte photos for the same area 5- 6 usually. Also analyse where exactly boats are anchored (monos and cats) on these pics. If for the area cant get good results, use my eyes and depth sounder at the approach. However this approach yields good results in 90% of cases.

It is better not to try to get perfect info but rather 'where I can go' info. Reading charts gives you false sense of security which can turn in disaster quick as I have learned.

[Breaking Waves]

Originally Posted by Simi 60

Thats not how you look at Sat images

Do tell - so how do you look at Sat images?

Originally Posted by arsenelupiga

Sorry duno what area is on the pic.

Its the harbour under discussion in this thread. would you take 2.1m draft in there based on looking at 'sat photos'?

[Squanderbucks]

I have been using Garmin chartplotters for years and a PC running various software packages with raster charts on the PC. My boating is all in South Florida and the Bahamas and I have to say that my experience has been that the charts on each source have been dead on.

My boat is setup with a CHIRP on one depth sounder and a 50/200 unit on the other. Both are set with a keel offset and calibrated to each other.
I run only the raster charts on the PC nowadays with OpenCPN because the vector chats for South Florida and Bahamas are pretty worthless. No detail at all. With no detail I haven’t bothered trying to check it’s soundings.

Many many times I have been amazed about how my depth recorders show exactly what’s on the Garmin within a foot or two. Shoals and reefs clearly where they should be in reference to my boat. Even compensated for estimated tide change effect ( of course a mathematical interpolation).
I do have a tablet with Navionics, Blue Chart and Active Captain but don’t use them while operating the boat - mostly for planning or uploading waypoints and routes to the chartplotters and PC.
I understand the foreign countries have more variation in their chart choices and sources and their accuracy may not be the same. Also South Florida and Bahamas do not have the large tidal swings of many other destinations (3 feet at most).

[Simi 60]

Originally Posted by Breaking Waves

Do tell - so how do you look at Sat images?

From overhead

I see rocks vs deep water quite clearly

[Breaking Waves]

Originally Posted by Simi 60

From overhead

I see rocks vs deep water quite clearly

would you take 2.1m in there? if so how far?

[conachair]

Originally Posted by Breaking Waves

curious - how do you know/get water depth from looking at a sat photo?

Sat images obviously doesn't give you sounding text but can be extremely useful to check the accuracy/datum of charts and will give a very good hint of depths, SasPlanet should, imho, be an absolute must have for a cruising boat. With keyboard shortcuts for the different sources. This is yandex sat, google sat, bing sat, navionics, cmap, navionics sonar. >

[CassidyNZ]

I’m astonished that there are folks in boats that believe that a satellite photo is better for navigation/pilotage than a marine chart. It absolutely beggars belief.

But then I guess there are folks that believe that the earth is flat.

Go figure. Anything is possible.

@Simi 60: is there any other way to look at a satellite picture than from overhead? What you can see is the difference between rocks and no rocks. See the depth? You’re kidding right?

[conachair]

Originally Posted by CassidyNZ

I’m astonished that there are folks in boats that believe that a satellite photo is better for navigation/pilotage than a marine chart. It absolutely beggars belief.

Did someone actually say that?????

Crazy.

Crazy as well not to use such a useful resource in addition to every other resource you can get your hands on as well. Sat images as chart files can be extremely useful cruising anywhere remotely remote.

[arsenelupiga]

this is how I would go about it:

first look at map to get an idea what we are dealing with and where is recommended route.

Then crosscheck several sat photos. One can conclude the following:

2.1m entry should be fine as one can see several monos in the harbour. In one of pics reasonable size mono is exiting so that clears that question.

One can see that coordinates do not align when looking at different sat pics and entry is narrow so GPS coordinates cant be used as one asks for more accuracy then there is.

Entry is around 13m wide and would take it in the middle.

the rest of the path would take deepest - darkest water that is clear of stones. Again, one would have to have reference points land marks and not GPS.

In the end compare path to the chart, hopefully in alignment else extra caution or further research.

This approach serves me well.

[conachair]

Originally Posted by arsenelupiga

This approach serves me well.

And a 3d sat image screen grab can be handy to get some conformation you're going to the right place in the real world >>

[raffo5]

Aqua Map looks correct

[Pete7]

Originally Posted by Breaking Waves

Do tell - so how do you look at Sat images?

Its the harbour under discussion in this thread. would you take 2.1m draft in there based on looking at 'sat photos'?

Only very carefully because I don't see any big yachts in there and the blob in the entrance could have a lifting keel. In my boat I would be happy to follow Carsten in because his draft is deeper than mine. We did have someone follow us in a similar shallow harbour entrance and it didn't end well for him, we have bilge keels

Some times its better to be the second mouse to the trap.

Pete

[conachair]

Originally Posted by Pete7

Only very carefully because I don't see any big yachts in there and the blob in the entrance could have a lifting keel. In my boat I would be happy to follow Carsten in because his draft is deeper than mine. We did have someone follow us in a similar shallow harbour entrance and it didn't end well for him, we have bilge keels

Some times its better to be the second mouse to the trap.

Pete

Don't forget google street view various marina web sites --





Even so , suspect most of us would have spoken to the marina to check and not just gone on one source of nav info known to be a bit suspect now and again..