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Bit of weather heading our way?


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better still if you turn on sonar view on your chartplotter, you will create your own chart overlay that is as accurate and extremely fine grained as your boats sensors will allow.

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6 minutes ago, Fish said:

Even better with Navionics Sonar chart. This from the web app.

Navionics ChartViewer

 

image.png.b99481e8ab57a641743107d1f8e0b29e.png

That chart shows the topography perfectly . The outside half of the point is a bigger but softer wave and the inside bit in by the shore is smaller but a steeper fun wave . We used to launch the boat at torpedo bay because the exposed ramps are out of the question when that place is breaking .

there are a few quality breaks on the mahurangi islands and mainland too , Scotts landing is the best place to launch from . A JetSki would make island surfing very accessible 

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2 hours ago, Psyche said:

better still if you turn on sonar view on your chartplotter, you will create your own chart overlay that is as accurate and extremely fine grained as your boats sensors will allow.

Tell me about this.

I have been looking at getting a small chart plotter that goes contour charts. (Our current Garmin is a generation too early for this and can't do it). Even the kayak fisho spec units will do 1 ft contours, so I was keen. But when I asked the supplier how to offset for tide height, he says it can't be done. Too much liability for Garmin (or anyone) to do that, or enable doing that.

He continued in saying the market for contours is the fisho crowd, and they are looking for structure. I would be looking for mapping anchorages so I know where I can park, how close in, and where the boogey rocks are. That said, I am developing an interesting in fishing, and it is always fun to know what is below the surface even if you are just sailing.

I've been pondering some way of processing data on a laptop to do my own hydrography, but then I just went sailing and haven't gotten around to it... I assume the Chartplotter data is in some format and extractable. Should just be a field in a gpx file or something. Possibly add the required offset in a gpx file (via csv?) then bung it back in the plotter? A bit of labour, but you would make your own bespoke charts...

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22 minutes ago, Fish said:

Tell me about this.

I have been looking at getting a small chart plotter that goes contour charts. (Our current Garmin is a generation too early for this and can't do it). Even the kayak fisho spec units will do 1 ft contours, so I was keen. But when I asked the supplier how to offset for tide height, he says it can't be done. Too much liability for Garmin (or anyone) to do that, or enable doing that.

He continued in saying the market for contours is the fisho crowd, and they are looking for structure. I would be looking for mapping anchorages so I know where I can park, how close in, and where the boogey rocks are. That said, I am developing an interesting in fishing, and it is always fun to know what is below the surface even if you are just sailing.

I've been pondering some way of processing data on a laptop to do my own hydrography, but then I just went sailing and haven't gotten around to it... I assume the Chartplotter data is in some format and extractable. Should just be a field in a gpx file or something. Possibly add the required offset in a gpx file (via csv?) then bung it back in the plotter? A bit of labour, but you would make your own bespoke charts...

The navionics sonar is crowd sourced and approximated, at 500mm intervals there isn't any certified more accurate plot.  LINZ does not even come close.

The navionics plot will record your depth across your track when connected to your boats sonar. 

What do you mean offset for tide height?  The contours displayed are LAT.

Here is our 24hr plot swinging around at anchor in Kirita Bay.   Eventually this will find its way into the navionics crowd sourced data and be available to everyone. 

Screenshot_20220114-160509_Boating.thumb.jpg.df6c9cdc6844cc12d48bc37e0df99346.jpg

 

 

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59 minutes ago, CarpeDiem said:

The navionics sonar is crowd sourced and approximated, at 500mm intervals there isn't any certified more accurate plot.  LINZ does not even come close.

The navionics plot will record your depth across your track when connected to your boats sonar. 

What do you mean offset for tide height?  The contours displayed are LAT.

Here is our 24hr plot swinging around at anchor in Kirita Bay.   Eventually this will find its way into the navionics crowd sourced data and be available to everyone. 

Screenshot_20220114-160509_Boating.thumb.jpg.df6c9cdc6844cc12d48bc37e0df99346.jpg

 

 

The concept of no 'datum reference ' for the cloud sourced data is a worry. Having a couple of metres of vertical randomness in the data is a concern.

What is the meaning of LAT as used above for how the contours are displayed?

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42 minutes ago, eruptn said:

The concept of no 'datum reference ' for the cloud sourced data is a worry. Having a couple of metres of vertical randomness in the data is a concern.

What is the meaning of LAT as used above for how the contours are displayed?

What do you mean 'no datum reference'? 

The numbers shown are what navionics has recorded from my depth sounder taking into account the tidal information and the transducer offset.

 

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What if some have a tranducer offset at 2.8m and someone has one at 300mm.....that has got to be a recipe for disaster if it gets shared publicly. Sounds dodgy to me unless it is kept to your own boat and device. 

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4 minutes ago, ynot said:

What if some have a tranducer offset at 2.8m and someone has one at 300mm.....that has got to be a recipe for disaster if it gets shared publicly. Sounds dodgy to me unless it is kept to your own boat and device. 

It adds them. The transducer offset is part of the nmea stream and is taken into account. My depth sounder was showing around 2.2 - 2.5m iirc.  The offset is 2.3m.

A risk would be faulty tranducers. I suspect that they mitigate this by using multiple readings from different sounders/vessels.  It is not clear how they pull the data together for public consumption but I suspect they err on the side of caution...

I have never found the sonar depths to be less than the chart datum or less than the actual depth. 

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image.png.1cd9257756cefa3479c2eeb6182bb9c6.pngWhy does Navionics show 2.7m around Sunday rock when minimum depth at bouy is 6m as per my sounder,never found it to be less the 6m anywhere around it.  How can a site be trusted when public can add marks to it,surely it should secure and you submit information for them to verify before posting??

There is another site I follow and some cracker going on about how he can stuff to navionics,surely that cant be true??reckons the channel/river he uses he has added a couple of rocks that arent on the chart.If that was the case why pay a fee for what is suppose to the latest update electronic charts. Paper shows how the rocks have indents etc around coast,navi seems to them as a grass strip😀

 

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4 hours ago, CarpeDiem said:

What do you mean offset for tide height?  The contours displayed are LAT.

 

 

This bit. Does your gear / navionics adjust for height of tide automatically?

Obviously somewhere along the line the depth seen (which is always going to be the depth at LAT plus the current height of tide) needs to be adjusted to a datum (i.e. LAT).

For the chart plotter I was looking at, I was told it would not do that. The Marine Electronics supplier I was talking to (a reputatabe one) stated that there weren't any products that would do I what I wanted (automatically reduce depth to a datum).

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1 hour ago, harrytom said:

Why does Navionics show 2.7m around Sunday rock when minimum depth at bouy is 6m as per my sounder,never found it to be less the 6m anywhere around it.

Because that's what's on the LINZ chart NZ5324. 

If you think this is wrong you could discuss it with LINZ. 

Sure you're talking about the same Sunday Rock? 

1418429368_Screenshot_20220114-201744_Multi-TIFFViewer.thumb.jpg.e5f2b4a73dd6fa8508f2ae849e3118a1.jpg

1 hour ago, harrytom said:

How can a site be trusted when public can add marks to it,surely it should secure and you submit information for them to verify before posting??

You can turn off the publicly provided information. Up to you. You can also edit them and even delete them. 

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4 minutes ago, Fish said:

This bit. Does your gear / navionics adjust for height of tide automatically?

Obviously somewhere along the line the depth seen (which is always going to be the depth at LAT plus the current height of tide) needs to be adjusted to a datum (i.e. LAT).

For the chart plotter I was looking at, I was told it would not do that. The Marine Electronics supplier I was talking to (a reputatabe one) stated that there weren't any products that would do I what I wanted (automatically reduce depth to a datum).

The numbers on my tablet screen detected by my transducer always are a minimum. So somehow it is deducting tide height from it. 

Eg, if I come into a bay at high tide with 6.5m of water depth, the navionics app shows 4.5m.

(assuming a 2m tide) 

If I sit at the same place for the next 6 hours, low tide, Navionics still reports 4.5m... 

So somehow it is doing the maths. Not clear if it's the zeus plotter or the tablet/app doing the maths. I don't know how it works in the backend...

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46 minutes ago, CarpeDiem said:

Because that's what's on the government provided paper chart NZ5324. 

If you think this is wrong you could discuss it with LINZ. 

Sure you're talking about the same Sunday Rock? 

1418429368_Screenshot_20220114-201744_Multi-TIFFViewer.thumb.jpg.e5f2b4a73dd6fa8508f2ae849e3118a1.jpg

You can turn off the publicly provided information. Up to you. You can also edit them and even delete them. 

I fish there 1/12 to end January ,kings and snapper,for about 6 weeks the gone.Been doing it or yrs.  19996.pngpaper chart 

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6 minutes ago, harrytom said:

I fish there 1/12 to end January ,kings and snapper,for about 6 weeks the gone.Been doing it or yrs.  19996.pngpaper chart 

Your paper chart is out of date. Get the latest from NZ5324 from LINZ.

But that's kind of irrelevant to your question, you asked... 

why Navionics says 2.7m

the answer is

because that's what the latest LINZ chart says

Navionics "chart view" uses the same base information as the LINZ charts.

So based on your local knowledge the LINZ charts are wrong. 

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6 hours ago, CarpeDiem said:

Your paper chart is out of date. Get the latest from NZ5324 from LINZ.

But that's kind of irrelevant to your question, you asked... 

why Navionics says 2.7m

the answer is

because that's what the latest LINZ chart says

Navionics "chart view" uses the same base information as the LINZ charts.

So based on your local knowledge the LINZ charts are wrong. 

I dont think so,  I use their site and  print A4 pages to suit areas that I want to get in close with or find structure ,handy site but does have limited charts,Good when at home you can move cusor around and zoom in and out,nn  https://data.linz.govt.nz/layer/51277-chart-nz-532-approaches-to-auckland

 

History
Added 18 Sep 2012
Last updated 14 Feb 2021
Revisions 16 - Browse all revisions
Current revision Imported on Feb. 14, 2021 from GeoTIFF in WGS 84.
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7 hours ago, Black Panther said:

Back to the weather, I can't really see anything that scary. Metservice says 40 kn in Colville for a few hours and that's it.

"Gale and storm force winds about Cyclone CODY, both offshore and as it approaches the northeast of the North Island, will generate large easterly swells, significant sea surges/rips and coastal inundation about exposed eastern coastlines."

 

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