A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: There are charts and there are CHARTS
From: Lu Abel
Date: 2015 Mar 7, 02:33 +0000
From: Lu Abel
Date: 2015 Mar 7, 02:33 +0000
Charts reflect two things: the coast line and soundings. On American charts many list the dates of soundings -- and the numbers are pretty astounding in many cases. Anybody remember when the QE II tore a hole in its bottom almost in Frank's back yard? Turns out that that the last survey of that area had been done back in the 1930s. Depthsounders existed, but only sounded the bottom with a narrow beam. The sounding ship missed a pretty large rock simply because it's back-and-forth path missed it. In some places in the US high-accuracy (breadth as well as depth) soundings are very important because big oil tankers (and, worse, liquified natural gas tankers) are plying the waters. What you really want is a sounding with what looks like the letter "I" lying on its side -- that means the area has been swept to that depth with a horizontal wire and nothing found.
In the US at least (and I suspect most of the rest of the world) national charting authorities give top priority to waters that will be used by commercial shipping. So re-surveys of areas used primarily (or exclusively) by recreational mariners are at the bottom of the list. A good example in the US is the Intra-Coastal Waterway. Originally used by barges and other small commercial traffic, it is now used primarily by recreational mariners. It's supposed to be dredged to 15 feet. It isn't, in many places there is severe shoaling. Worse, charts of the area are not kept up-to-date. The best people traversing these areas have is the possibility (but not a promise) that the Coast Guard will relocate buoys to follow the channel as it shifts.
From: David Pike <NoReply_DavidPike@fer3.com>
Sent: Friday, March 6, 2015 3:26 PM
Subject: [NavList] There are charts and there are CHARTS
"almost-landlocked Germany" Better not tell the Germans. Have you looked at your atlas recently. it's about 130 miles from Borkum to Sylt, and about 260 miles from Flensburg to Poland. They built the Kiel Canal to move their Naval Fleets swiftly from the Baltic to the Noth Sea and vice versa. The West Coast Rivers contain some of the Worlds greatest ports.
"NV produces top quality charts, thank goodness...but it seems odd that you get better BVI charts from almost-landlocked Germany than you do from the British themselves." NV Chart folios are very good, I used them in the Baltic, but have you wondered where they get their original soundings from. Did they send a survey team to the BVI to re-survey the waters, or did they obtain their information for an existing source, posibly the UK Hyrographic Office?
"the last survey date is "more than 100 years ago" This is not uncommon on many charts. In this accountancy led World, the trend is to mainly survey the places where the commercial vessels are most likely to sail. The Lower Humber is surveyed annually with the dredged chanels surveyed more frequently. The Upper Humber is surveyed bi-monthly or more frequently as required. At least British Admiralty charts inculde a panel showing the dates of the last full survey. Not all other charts do.
Where was I? ...oh yes, the British and their charts. They are simply not players in cartography, even when it comes to their own territorial posessions. Presumably in home waters (other than the Scilly Isles!) they try to keep up to date, but not in this hemisphere. Once the British mechantile and Naval fleets were the largest in the World and labour was cheap. If the UK Hydrodrographic Office has a millstone around its neck, it's its legacy of World Wide Crart Coverage to support, when there's much less UK commercial demmand. Go to the NV and UKHO websites and look at the relative coverage. You can see why the UKHO has a job on its hands. Companies like NV can concentrate upon producing for the markets and places where the demmand is greatest.
"The Canadians keep their charts up to date, like the Americans, on a month by month basis through a publication called "Notices to Mariners." So does the UKHO: they also sent official agents traces of the corections to make life easy. Corections are now availabe on the WWW.
It's also inportant to realise that much original World hydrographic soundings and even chart production is shared between the various maritime nations.