Notices to Mariners

[Lizman]

Hello,

I have a second-hand map of Scilly, SC883, 1998, corrected to 2002 by the previous owner. I tried to correct it using the UKHO site but was only able to get corrections for the years 2014, '15, and '16. I was told by UKHO when I rang them that they stopped providing corrections for older editions because they were considered 'navigationally unsafe'. I have contacted their customer services for clarification. Does seem a shame as the chart is vgc. Just wondered whether anyone here has any comments?

lizman

 

[[70521]]

I'd view a chart of that vintage quite up to date. Its not as if the islands move about much and tend to treat any movement around there as pilotage with the MK I eyeball.

 

[marklucas]

As stated the rocks don't move.

Having been to the Isles of Scilly three times across the period you mention, the only change I can remember is a new West Cardinal for Steeple Rock - but of course you would been using a bearing on St. Agnes lighthouse so this is only good news.

 

[awol]

First, it's not a "map", it's a "chart". NtMs are available for an issue of a chart until a new issue is released. At that point the previous NtMs are removed from the website and the process starts again. This then raises the question "why was a new issue of the chart made?" It is not done on a whim and is usually because the amount of change information is greater than a magenta pen can cope with. The addition of a cardinal mark is unlikely to be sufficient reason.

 

[Minchsailor]

This then raises the question "why was a new issue of the chart made?".

Change of datum? Not important if navigation is by old fashioned eyeball, which in normal conditions in the Scilly Isles is the case - but you would need care in poor vis.

I would be quite happy using a chart corrected to 2002 in the area.

 

[Seven Spades]

Hello,

I have a second-hand map of Scilly, SC883, 1998, corrected to 2002 by the previous owner. I tried to correct it using the UKHO site but was only able to get corrections for the years 2014, '15, and '16. I was told by UKHO when I rang them that they stopped providing corrections for older editions because they were considered 'navigationally unsafe'. I have contacted their customer services for clarification. Does seem a shame as the chart is vgc. Just wondered whether anyone here has any comments?

lizman

If your chart is WGS84 then I would say cobblers and carry on using it. The only things likely to change are the positions of navigational marks.

 

[awol]

According to my (out of date!) chart file the coast of St Mary's from SW to NE was resurveyed in 2012-2013 by the Duke of Rothesay himself, or at least by the Duchy of Cornwall. Whether anything there affects the OP's boat, I haven't a scooby.

 

[marklucas]

The addition of a cardinal mark is unlikely to be sufficient reason.

Quite true, but something has to tip the list to make it worth issuing a new chart.

 

[Lizman]

Yes,

I see that the positions are referred to the 1936 datum on my chart, so if there where substantial changes following the resurvey, justifying block changes, it would have made a bit of a dogs breakfast of things. No matter, I have 2014 Reeds, and will use it to add/modify any beacons.

Thanks for the advise.

Lizman

 

[awol]

The change from OSGB36 to WGS84 would justify an issue change. I am presuming the OP understands they are different and plotting the position from a GPS set to WGS84 onto a OSGB36 chart may not be a good idea. There is a conversion programme at http://www.movable-type.co.uk/scripts/latlong-convert-coords.html

Edit: just checked and the difference is ~0.5 cables to the SE or NW depending which way you are going

 

[bitbaltic]

The change from OSGB36 to WGS84 would justify an issue change.

Definitely.

I am all for the continued updating and use of superceeded charts, especially if they've been continuously updated and are in good condition (this chart is only halfway to that). However OSGB36 would be a show stopper. The 5 ca offset to WGS84 might or might not be an issue but i think it's worth spending a few bucks not to have to worry about that one.

 

[Lizman]

Hi Awol,

Thanks for the conversion programme. It will come in handy when I get some computing power on board. At the moment I don't even have a smartphone. It'll come.

Yes, I am aware of the shifts in lat and long with the different datums. I have started transferring fixes from gps to charts with distance/bearing of local landmarks rather than transferring lat/long, which I find very cumbersome and slow, especially in a moderate sea.

Best Wishes and Good Sailing
lizaman

 

[bitbaltic]

I have started transferring fixes from gps to charts with distance/bearing of local landmarks

Is there a compass rose on your charts? If you make the centre of that a waypoint in your GPS, you can just measure the 'distance to waypoint' back along the recipocal of the bearing to plot a GPS fix. Easier than using landmarks as they won't usually have a rose around them so you will have to measure the bearing too. Also works when there is no landmark on the chart (ie in open water).

Cheers

 

[Lizman]

Hi Bitbaltic,

I do see the advantage of the compass rose method, especially in open water, but it would involve creating a lot of waypoints, some of which would need to be adjusted for a different datum (ed1950, osgb1936), and the potential for mishap, for me, would be very large. Transferring bearing/distance seems more intuitive, less room for snafu, but that's just me.

Best Wishes
lizman