I've been thinking ......... well it is winter! Is there such a product on the market that displays live chart depths on a chart plotter all over the charted area?
Surely we have the technology to integrate GPS position, hydrographic data, time etc. etc. into a chart plotter which would then enable the plotter to indicate live depths over the entire chart. Would it be useful for course plotting in what may be tight depth areas? Actual boat position could be accompanied by the depth sounder reading popping up in a local balloon. Of course it'd be wise to plot the original CD (or have it as an optional layer) just to keep a watchful eye on things.
If they have the techno to plot live AIS positions including target vessel SOG, COG, destination etc. they must be able to do some jiggery pokery with all the info available on some of today's high tech boats.
This would also apply to predicted wind speed and direction, live tidal data (from bouys and AIS transponders on vessels in the region).
Does such an animal exist?
Location: 'ang on a mo, I'll just take some bearings
Posts: 17,178
Given the several variables involved in tide height guessing, why would you trust it, even if it could be cobbled up?
And, err, the sounder gives actual depth at actual time and actual position, provided it's been calibrated.
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My Raymarines have "live" tidal data with Navionics charts ............ but why not live depth ?
I'm talking live depth all over the chart not just in the actual location of the vessel. Why display CD depths when it's possible to display live actual depths across the whole charted area ?
It could only ever be a theoretical 'depth'. The only exact depths are at tide gauges. Now here in the Thames Estuary you could get the height of tide at a particular time at say Walton and another at Sheerness. The height at Walton could be above, on or below prediction, ditto Sheerness. You can get it above prediction some days at Walton while at the same time below prediction at Sheerness. So you would have to have a formula in the software to work out depths at positions in between in addition to sucking down the data on tide heights from somewhere. On what basis would the formula depend? There is no data available that says whether a point midway between those points would be above, below or on prediction. You could say, well lets average it so you get an approximation. What's the point of an approximation? Who is to say how accurate the depth is anyway. It is no more than what was found on a particular day. OK over your rocky shores I guess but over here we could take you to a spot that is charted at 8 metres but actually last October had no more than 8foot of water.
It seems a nice idea but.... When we see a chart we know that the depths are subject to variation and make our judgements accordingly. If it purports to give a height of water at that exact time, we would expect it to be accurate. But would it? Sometimes yes, sometimes no.
Location: 'ang on a mo, I'll just take some bearings
Posts: 17,178
One: because tides don't rise and fall in accordance with some neatly encoded formula, they get buggered about by atmospheric pressure, winds, river water flows, silting, shifting banks and Neptune's inside leg measurement.
Two: because actual tidal curves have only ever been constructed for a few coastal points. What happens in between is interpolation/best guess and mostly is never checked except by wafis like us when the lugger comes to a grinding halt.
Three: because the height shown other than where you are, won't be the same by the time you get there.
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There are three kinds of people:
Those who learn by reading.
Those who learn by observation.
Those who have to pee on an electric fence for themselves.
Smart charts/plotters - do they exist?
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