New Solent banks drying above CD according to iPad Navionics

[AntarcticPilot]

Clearly this is data from UKHO but it does look like a survey error. I wonder if there was a high pressure on the day the survey took place. The area near peel bank is very shallow, I passed over this area during the summer and was surprised at how little water there was. I was perviously berthed in Haslar so used to sail over this area regally, but returning after a few years absence I noticed the difference. I suspect that the survey has the profile of the seabed correct but it is possible that due to high pressure on the day of the survey the actual measurements are out by an amount. I doubt that Peel Bank and Bramble bank were surveyed the same day, because we know that Bramble dries and Peel does not.

Marine survey certainly takes into account things like barometric pressure, and everything else that can cause changes in sea-level. Measurements are done using DGPS relative to fixed, shore-based datum points, so what is determined is the absolute height of the sea-bed, not merely the depth at the time of survey. I should note that this isn't the broadcast DGPS we all have access to; it is survey grade kit good to a centimetre or better.

 

[Angele]

Looking at the recent NtoMs for the Solent leisure chart folio (SC5600), there appear to be numerous changes to depths, but none includes a new printed block so difficult to say how material they are. They simply give a general comment along the following lines:

Notices to Mariners - Weekly Edition 11/2013 International Chart Series,
England – South Coast, Eastern Approaches to The Solent.
Page 11 of 20
— Chart 2037 — New Edition Announcement.
Charts SC5600·13, SC5600·17 and SC5600·19 WGS84 DATUM
The following changes were published in the new edition of chart 2037, which is the source chart
for the above folio sheets:
Includes changes to depths from the latest ABP Southampton, British Government and
commercial surveys. Mariners should therefore navigate with caution on sheets SC5600·13,
SC5600·17 and SC5600·19 and be aware that any subsequent Notices to Mariners applied
to these sheets are issued for information only.
These changes will be included in the next new edition of SC5600.

With unhelpful NtoMs like this, either we ditch all our old charts and buy a new one when the next edition comes out or we stick to the white bits (ideally following in the wake of something big and orange - e.g. Hanne Knutsen).

 

[Angele]

For what it's worth I can well believe that the Brambles is sinking - about five or six years ago I landed on it with the works dinghy club and we had loads of space to run about on; the annual cricket match this year was a very damp affair with only a tiny patch drying a few inches above the sea.

Anyone know how we go about booking Peel bank for the inaugural Solent Scuttlebutt rugby match?

How about August 13, 2014? LW Pompey 06:01UT 0.3m

 

[prv]

With unhelpful NtoMs like this, either we ditch all our old charts and buy a new one when the next edition comes out

I believe that's always been the case if you want to remain up to date. The Admiralty provide a limited overlap period (but wholesale depth changes due to new survey can't really be expressed properly as NtoMs) and Imray just kill the old edition immediately and remove the corrections from their website.

Pete

 

[prv]

Anyone know how we go about booking Peel bank for the inaugural Solent Scuttlebutt rugby match?

Just turn up with the biggest flag, I reckon

How about August 13, 2014? LW Pompey 06:01UT 0.3m

If we think there genuinely will be a decent chunk of sand above water, then I'm well up for that.

Pete

 

[Angele]

Just turn up with the biggest flag, I reckon



If we think there genuinely will be a decent chunk of sand above water, then I'm well up for that.

Pete

If they really are correct, then there should a patch, vaguely rectangular, measuring about 600m x 300m poking out at low water.

Personally, I don't believe any of this, or we would have all been running aground this year on our way to anchor off Osbourne Bay - especially those coming from Portsmouth.

 

[Angele]

I believe that's always been the case if you want to remain up to date. The Admiralty provide a limited overlap period (but wholesale depth changes due to new survey can't really be expressed properly as NtoMs) and Imray just kill the old edition immediately and remove the corrections from their website.

Pete

... but if the changes are too big to encompass with a "insert 4.5m in posn lat/long surrounded by a 5m depth contour" then they usually provide a new block to print off and glue onto the chart. I'm guessing these changes are too significant/widespread to treat in this fashion.

 

[Cohoe]

Popped out of Portsmouth using the inner passage today. 2.4m on a rising tide about noon. Sighted the tidal gauge at 2.2m and turned hard to Starboard leaving the BC OUTER to Port and the sea wall about 50m to Starboard. The Depth gauge fell to a minimum of 1 .2m under my 1.6m draught keel. So thats 2.8m of water at 2.4m of tidal height. So the old charted depth of 0.3m is still pretty accurate. The new Navionic chart says the spit now extends out well beyond BC Outer towards Hamilton Bank and dries 1.2m above CD. I'm rapidly loosing faith in the new Navionics chart update. So Im off to go and sound the allegedly drying banks at Peel bank and Mother Bank. Pretty sure the Solent hasn't changed much its just duff chart updates. Will let you know.
Rgds Cohoe

 

[Twister_Ken]

but I never managed to find it, similarly the sub. barrier between NMLF and Ryde was reported but never seen.

That was deleted many years back. Way I heard it, most of the concrete blocks slowly sank into the sand they were sitting on, and military divers exploded the rest.

 

[Twister_Ken]

I'm also convinced the N Channel (Gilkicker towards Calshot) and the inshore areas off Hillhead and Lee on Solent are considerably shallower than they were when I was racing around there regularly back in the 1980/90s

 

[Angele]

Popped out of Portsmouth using the inner passage today. 2.4m on a rising tide about noon. Sighted the tidal gauge at 2.2m and turned hard to Starboard leaving the BC OUTER to Port and the sea wall about 50m to Starboard. The Depth gauge fell to a minimum of 1 .2m under my 1.6m draught keel. So thats 2.8m of water at 2.4m of tidal height. So the old charted depth of 0.3m is still pretty accurate. The new Navionic chart says the spit now extends out well beyond BC Outer towards Hamilton Bank and dries 1.2m above CD. I'm rapidly loosing faith in the new Navionics chart update. So Im off to go and sound the allegedly drying banks at Peel bank and Mother Bank. Pretty sure the Solent hasn't changed much its just duff chart updates. Will let you know.
Rgds Cohoe

Keep us posted on your findings.

If it turns out it really does exist as an island at low water, can you claim it with your Scuttlebutt burgee, together with the following note "reserved for Scuttlebutt rugby match 13 August 2014 - bring your own beers"?

 

[DJE]

I regularly use the route between Blockhouse and BC Outer and I reckon there is about 0.5m at CD through there. Well there was when I was last there about a month ago.

 

[ParaHandy]

... The new Navionic chart says the spit now extends out well beyond BC Outer towards Hamilton Bank and dries 1.2m above CD. .... Pretty sure the Solent hasn't changed much its just duff chart updates. Will let you know.

Thanks for that. My iPad Navionics chart must be an earlier version as it shows the Inner Swashway as I know it. I cannot update my charts as I have not paid the £37.99 for upgrades (new this year) and am unlikely to now.

 

[Martin_J]

And it's strange how the Inner Swashway appears to have become more inaccurate whilst the West Winner has become more accurate.

Peel Bank has yet to be proven.

 

[Angele]

[snip]

Peel Bank has yet to be proven.

.... or seen at low water would be a good start. If it really is 1.4m above datum, why aren't there photos of it on the web?

 

[richardbrennan]

I am hoping to go to Cowes from Gosport on Sunday and will, if possible, check out the Inner Swashway. I think 05 at CD is, or perhaps that should be was, about right. I generally use a figure of 2.4 from QMH as to whether I use it or not, which with my draft of 1.8 would give me my minimum of 1 meter under the keel.

 

[Cohoe]

I can now state with some conviction that the chart updates for the Solent that appeared on Navionics and Paper charts are inaccurate. The suggestion that Peel and Mother Banks are dry at CD is inaccurate but they are shallow. The Bramble Bank cricket match is safe.

My observation Tuesday 26Nov2013. I sailed Paperchase II over them both at about 2.5m height of tide at Portsmouth. With very high pressure suppressing the tidal height, possibly by 0.2m.

Conclusions
Mother Bank at 50 45.2N 001 12.6W is 2.1m below CD Shallowest point having sailed its charted length.
Peel Bank at 50 45.5N 001 14.1W is 2.2m below CD at its shallowest having sailed its charted length.
The previous paper charts give similar soundings.

Perhaps we should email UKHO & RYA. Perhaps they know why the charts show inaccurate soundings and new drying Banks.

For those of you using the inner passage into Portsmouth via the Haslar sea wall and BC Outer the depth there is much the same too. About 0.4m below CD measured yesterday. The new charted drying spit extending out to Hamilton Bank past BC Outer does not dry.

Regards Cohoe

 

[Angele]

Perhaps we should email UKHO & RYA. Perhaps they know why the charts show inaccurate soundings and new drying Banks.

I did that yesterday (the UKHO that is). Not having sailed over it recently (*Edit), my arguments were based on:

1. If it is at 1.4m above datum, why has no one seen it?
2. If it is at 1.4m above datum and yet no one knows of it as a hazard (and it is not buoyed as such) why aren't people hitting it all the time?

It would be good if you could send them your observed data, as I suspect it will be more persuasive.

I rang them and they told me to send my query to customerservices@ukho.gov.uk - which I did. I haven't received any reply or acknowledgement (but I only sent it at 17:00 yesterday).

Edit: actually, I have, but just not watching the depth closely - after all, why would I? It isn't a hazard - rather proves my point.

 

[Ru88ell]

Very interesting. I'm happy to go in the forwards.

 

[Angele]

A response:

Thank you for your enquiry below.

You are correct; there is a NE (15) of SC5600 dtd 21st November 2013. However this shows the same hydrography in the areas in question as the folio you have dtd 16th August 2012 (14). You will also note that SC5600 does not show the drying banks you are questioning as depicted on the Navionics chart.

UKHO have recently received a survey which has been assessed but not included on any products to date. This covers the areas of interest and I can confirm the depths are in close agreement and support the depiction you currently see on SC5600, the drying patches in question are not shown.

I would suggest you contact Navionics to ascertain what source material has been used in the generation of their product as they are best placed to answer your query. We would be interested to know where Navionics acquired their data.

Best regards.

I'm very impressed with the speed of that response. Very good UKHO.

Mystery deepens though ....

.... add to this the fact that I don't seem to be able to access the Navionics webapp at the moment.