Bad Navionics map

[aliyesami]

I just subscribed to Navionics on Android app and was looking at the potential gulf area where we plan to buy a house. The canal depths for one of the person I know who owna s 40ft boat is shown as 0-3 ft . When i asked the guy he said the depths are 5-10 ft based on the tide which makes sense and his neighor has a 60ft boat.
How can Navionics chart be so wrong and can we rely on them ?
The blue line in the attached Navionics map is the route he takes . And not only wrong depth , near the marina the canal is showing totally blocked (green color) , which is also not correct .

 

[Baddox]

Green on my Navionics charts shows depths less than zero; in other words a drying area. Around here this will be the chart datum depth or lowest astronomical tide so green areas would usually be covered with water at a depth defined by the tide minus drying height.

 

[tillergirl]

Navionics never conduct surveys. They rely on information primarily from national charts and on information from local harbours/authorities. Unfortunately Navionics (and indeed all leisure echart makers as far as I know) do not tell us how recent the data is. I could take you the east coast of England and show you a UK national chart which details how recent all parts of the chart are. Some parts will be right up to date while other parts which are commonly used by leisure craft were last surveyed in 1986. The cost of surveying is such that most goes to commercial areas. But unfortunately echart updating isn't necessarily great. Best see what the locals say.

 

[dunedin]

I just subscribed to Navionics on Android app and was looking at the potential gulf area where we plan to buy a house. The canal depths for one of the person I know who owna s 40ft boat is shown as 0-3 ft . When i asked the guy he said the depths are 5-10 ft based on the tide which makes sense and his neighor has a 60ft boat.
How can Navionics chart be so wrong and can we rely on them ?
The blue line in the attached Navionics map is the route he takes . And not only wrong depth , near the marina the canal is showing totally blocked (green color) , which is also not correct .

Which country are you talking about?
And what does the official country chart say for the area you refer to?

Navionics starts with the official hydrographic office data, if there is any.
In some places this is generally fairly complete and accurate - particularly where large ships go.
In other places there are major gaps where waters have never been surveyed, or in some cases where the survey (done in rowing boats with lead lines and sextants) may be out of alignment - they didn’t have differential GPS or any electronic aids when surveyed.

And of course the depth in the channel depends on the height of tide. There are countless places where boats can go at high water but not at low water.

 

[tillergirl]

Which country are you talking about?

Pretty obvious. USA

 

[dunedin]

Pretty obvious. USA

There are multiple places called Cross Bayou - but yes that would be my guess also.
Hence the official charts the OP should be comparing with are NAOO issued.
But also depends where the NAOO see the cutoff with inland waters- huge area of USA lakes have apparently never been surveyed, hence the driver to develop the crowd sourced techniques was for these areas in America.
But the waters in question seem to be tidal (though OP's comments about tude heights are ambiguous). Agree local knowledge will be key.
PS I am.advused that Navionics do sometimes commission their own commercial surveys to fill key gaps, though this is rare (at least in UK waters)

 

[jon and michie]

As what @Baddox says - on my Navionics chart green is drying out area but you can choose overlays ie depths marked with or without etc.
you mention it is on your android app - assume for your phone could this navionics version be a little limited vs a standard onboard chart plotter ?

 

[wonkywinch]

The OP is near New Port Richie to the NE of Tampa. The tidal range around there is less than a metre (3 feet) and there looks to be so much waterside property development around that area, I wouldn't rely on charts or hydrography unless it was done yesterday as those channels will either be silted up or newly dredged by the developers.

Perhaps the OP could go out at low springs and map the route by following a real depth contour, finding out where that is on both sides of the channel then save that as a track for future reference?

Cross Bayou

 

[requiem]

Here's the current NOAA chart for that area. The source date is listed as August of 2013, but the survey dates are 1950-59. I checked Aqua Map for US ACE survey data, but no joy. Navionics' sonar chart layer may be the best option here.

 

[Minerva]

Here's the current NOAA chart for that area. The source date is listed as August of 2013, but the survey dates are 1950-59. I checked Aqua Map for US ACE survey data, but no joy. Navionics' sonar chart layer may be the best option here.

View attachment 204872

That’s erm, quite an interesting layout of pontoons. Lots of “nice” 90° legs to the reich. Bet it’s popular these days.