Crossing the Spitway 2025

tillergirl said:
PLEASE, PLEASE, DO NOT RELY ON NAVIONICS AT THE SPITWAY.
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Understand the warning here - and certainly I would favour the sources you've mentioned for charted depths over Navionics. I think in @John_Silver's post he was talking about using the Navionics tide time / height information, but suggested using your chartlet for the actual depth readings.

Out of interest, do you have any insight as to why Navionics is unreliable around here? Is it to do with their community-collected depth data do you think? Is it an issue that other chart sources would also suffer? (I use Orca which is based on the standard UKHO-released charts)
 
Matt, good question. I started to explain and I droned on and on and now I have to some domestic duties so I will post this afternoon. Navionics also uses standard UKHO charts - well its blurbs says that!
 
At the end of the season last year I had noticed some slow updates on Echarts. As you know I monitor the SE coast NtMs which is part of trying to keep the book up to date. When the boat came ashore, I took the chart plotter home and fitted it up so as I had Navionics in subscription I could monitor changes every day. I selected relevant NtMs to monitor and I followed it daily from 8th November to 27th April before all the kit went back to the boat. I have continued to do some monitoring using the on-line chartviewers of C-Map and Navionics. I evidenced changes (or lack of changes) so I have 59 pages of images and 44 pages of text explaining and identifying 'issues'. I thought of writing an article but frankly explaining the issues is quite tedious and too long for an article. To criticise needs evidence and displaying the evidence rather does go on. I have only mentioned one place and I will not mention others obviously as I wait to see if Echarts amend the particular issues. But at the spitway, C-Map's performance is much better than Navionics.

I (momentarily) was surprised that no yachting magazine has tried to do an objective test of Echarts. But it needs a lot of time and quite a bit of money to have every different Echart in subscription ...... and to read each NtM! Echarts claim to be updated. What does that mean? What is prompt enough, a day, a week, a mont? Best you have patience for 4 months but some changes are done quickly, some haven't been done for nigh on 4 months. Are all the changes critical? Well, that's a subjective view most of the time. I think there is also so many other issues such as what is displayed at different zoom levels, their 'understanding' of how to display amendments properly, where 'ghost' issues appear or being able to see marginal notes (from paper charts) [C-Map doesn't trouble you about those, Navionics does but I reckon you need a degree in Echarts to find them easily].
 
tillergirl said:
At the end of the season last year I had noticed some slow updates on Echarts. As you know I monitor the SE coast NtMs which is part of trying to keep the book up to date. When the boat came ashore, I took the chart plotter home and fitted it up so as I had Navionics in subscription I could monitor changes every day. I selected relevant NtMs to monitor and I followed it daily from 8th November to 27th April before all the kit went back to the boat. I have continued to do some monitoring using the on-line chartviewers of C-Map and Navionics. I evidenced changes (or lack of changes) so I have 59 pages of images and 44 pages of text explaining and identifying 'issues'. I thought of writing an article but frankly explaining the issues is quite tedious and too long for an article. To criticise needs evidence and displaying the evidence rather does go on. I have only mentioned one place and I will not mention others obviously as I wait to see if Echarts amend the particular issues. But at the spitway, C-Map's performance is much better than Navionics.

I (momentarily) was surprised that no yachting magazine has tried to do an objective test of Echarts. But it needs a lot of time and quite a bit of money to have every different Echart in subscription ...... and to read each NtM! Echarts claim to be updated. What does that mean? What is prompt enough, a day, a week, a mont? Best you have patience for 4 months but some changes are done quickly, some haven't been done for nigh on 4 months. Are all the changes critical? Well, that's a subjective view most of the time. I think there is also so many other issues such as what is displayed at different zoom levels, their 'understanding' of how to display amendments properly, where 'ghost' issues appear or being able to see marginal notes (from paper charts) [C-Map doesn't trouble you about those, Navionics does but I reckon you need a degree in Echarts to find them easily].
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Interesting that in your experience you've found CMap to be more responsive to changes than Navionics - it's certainly challenging a preconception I had that Navionics was generally the most responsive to things like constantly shifting depths etc due to the community contribution aspect!
 
tillergirl said:
I dare not speak about community contribution aspects! Of course some are good and others ..........
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My views on this are probably well known, but the situation is that there are aspects of Navionic's crowd-sourced data that make it dangerous in places; examples abound on these fora! But in summary, crowd-sourcing depends a) on there being a crowd, b) that there be a means of eliminating bad data and c) that data not be extrapolated beyond the bounds of the data. Sadly, Navionics falls down on all three, the last being the most dangerous.
 
What is the uncertainty in depths we are talking about here.

I normally wouldn't be happy anywhere without a couple of metres to spare under the keel in case there was a (new) hump. I've been caught out a couple of times with depth being a lot shallower than previously. Last time thought the echo sounder was faulty but no.
 
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Egret said:
What is the uncertainty in depths we are talking about here.

I normally wouldn't be happy anywhere without a couple of metres to spare under the keel in case there was a (new) hump. I've been caught out a couple of times with depth being a lot shallower than previously. Last time thought the echo sounder was faulty but no. Like the seafarer still, as if it it not certain it gives a wide band of possible depths and you make the judgement.
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That would exclude most of out favourite courses or destinations. I am generally happy with something like half a metre at somewhere like Pye End, to take into account tidal variations and my own miscalculation. It is a long time since I went through the Spitway, where variations in the channel are greater, but anything around a metre would be fine, and probably a lot more than I would expect when I used to sail from the Blackwater.
 
Egret said:
What is the uncertainty in depths we are talking about here.

I normally wouldn't be happy anywhere without a couple of metres to spare under the keel in case there was a (new) hump. I've been caught out a couple of times with depth being a lot shallower than previously. Last time thought the echo sounder was faulty but no. Like the seafarer still, as if it it not certain it gives a wide band of possible depths and you make the judgement.
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The difference isn't large - 0.3m. On Navionics the worst depth at the moment is 1.3m east of the line between the buoys but 4 months ago UKHO updated the depth to 1m where we found 1 metre CD last year in line between the two SWBs. I am suggesting you can find 1.7m to the east. (I did actually send the data into Trinity House and suggested it might be useful if they put the buoys further to the east. They did acknowledge but I have hear nothing further and perhaps they haven't needed servicing).

For some 0.3 of a metre (9/10 inches) isn't the end of the world but trying to time some sufficient height of tide for a 1.7m keel does at least needs the best data as a starting point. For not having updating a change for 4 months is hardly the kind performance some of us expect.
 
tillergirl said:
The difference isn't large - 0.3m. On Navionics the worst depth at the moment is 1.3m east of the line between the buoys but 4 months ago UKHO updated the depth to 1m where we found 1 metre CD last year in line between the two SWBs. I am suggesting you can find 1.7m to the east. (I did actually send the data into Trinity House and suggested it might be useful if they put the buoys further to the east. They did acknowledge but I have hear nothing further and perhaps they haven't needed servicing).

For some 0.3 of a metre (9/10 inches) isn't the end of the world but trying to time some sufficient height of tide for a 1.7m keel does at least needs the best data as a starting point. For not having updating a change for 4 months is hardly the kind performance some of us expect.
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I think that if it were me, I would follow the marked channel and use your information so that I would know which way to go if it were shallower than desired.
 
xyachtdave said:
OP, I wouldn’t over complicate your trip across the Spitway, play it safe on Friday and get there before 18.00 or after 20.00.
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I think this is most likely what my timings are going to look like anyway. Leaving Chatham at 1430, so quite unlikely I'll hit the spitway before 2000 and if I made that good progress I'll just slow down :) Schedule not necessary to take any risks, and I can't get into Brightlingsea until there's some water anyway.
 
MattS said:
I think this is most likely what my timings are going to look like anyway. Leaving Chatham at 1430, so quite unlikely I'll hit the spitway before 2000 and if I made that good progress I'll just slow down :) Schedule not necessary to take any risks, and I can't get into Brightlingsea until there's some water anyway.
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Have a great trip and I hope there’s more East than North in the NE wind for you.
 
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