Chart corrections

So I mentioned in passing that I picked up a good set of charts this weekend at the annual Fisheries Supply swap meet. This is all well and good, but when you get used charts, you have to make sure that they are up to date, or plan on using that money you saved to patch the hull after you run into that new shallow wreck that isn't shown on them.

Although they were all in excellent condition, none of the charts I picked up had been corrected by their previous owners and the earliest among them was printed back in the late nineties. That is a lot of years of corrections to go through, for a pretty sizeable patch of Canadian waters! I'm a bit bug-eyed today after have gone through almost all of them over the weekend.

If you haven't done this before (and you probably haven't, based on what I saw from most of those both selling and buying charts at the swap meet), you'll find that the relevant agencies (the Canadian Coast Guard for Canadian waters and the National Oceanic and Atmospheric Administration for US waters) make it very easy to do so. All updates are handled in both countries through their respective Notices to Mariners (NTM). The links above go directly to the archives of all NTMs, searchable by chart and date.

First, you have to find when the chart was issued and/or last corrected. Although most private sellers don't correct their charts, registered chart agents, as a matter of law, do. In the lower left corner of the chart you'll find the date of the current edition, previous editions, and a line which says "Notices to Mariners." Adjacent to the Notices to Mariners line you may or may not see a number of dates (see photo above). These indicate the dates to which the chart has been manually corrected. Chart agents, at least until the advent of print-on-demand charts, would carry a stock of charts. Obviously some of these become outmoded sitting on the shelves; rather than throw them out, the agents correct them to a current NTM date and sell them. So, your job becomes easier the more recently the chart was sold by a reputable chart agent--you find the most current date of NTM corrections, and only pull up NTMs subsequent to that to correct from.

You may have further difficulties if you have purchased charts from a third-party chartmaker. There's no such thing in Canada, but a number of US companies produce reliable charts directly from NOAA's free digital chart products. These charts don't always correspond directly to particular NOAA chart numbers, which can be good--the layouts often are far better matched to actual cruising routes and you don't end up navigating at the edges of charts so much. But since they are made of an amalgamation of NOAA charts, you have to find NTMs for each of them, some of which will be on the portion used for the private chart, and some of which will not. It's a drag; we use Maptech's excellent waterproof chartbooks for the Puget Sound and San Juan islands and I went through and updated them at the same time. Although they are far more recent (only 1 year of corrections to go through) it took me as long to do them as all the Canadian ones.

After that, it becomes laborious. Anything can be a candidate for correction, from the text of the Advisory notes to depths to changed navaids. Obviously these are of varying importance. Personally, I'm not going to change all the French text on a Canadian chart regarding the horizontal datum. At the other extreme, I damn sure am going to note a channel buoy that has been removed. I did learn to read through all the NTMs before making any changes, though; frequently, a note regarding a disabled navaid will subsequently be repealed by a later NTM when the problem has been fixed. No sense crossing something out and having to add it in again later.

Making the actual corrections on the chart varies from easy to quite difficult. The location of each correction is provided in latitude and longitude, so you simply locate the point with standard navigational tools and add or subtract whatever the correction calls for. For a navaid which has had the horn removed, for example, a simple black line through the Horn indication is no problem. Adding in a marker for a new buoy is a little harder; I'm not much at freehand drawing and some of the symbols from Chart 1 aren't particularly easy to draw, particularly if they need to be inserted (as buoys often do) in locations which are already very tight on space. I also found it difficult to add in area markers--all additions and subtractions are provided with lat/long coordinates, but when you have a circular area that has been designated Spoil ground, it's not that easy to get it in properly. Same with new breakwaters, dolphins, and the like.

Once you get your charts up to current, it's fairly easy to keep up (provided you have a fairly consistent set of cruising grounds--if you range around the world, you're always going to be running into something new, it seems). You should probably be regularly checking local NTMs anyway, and it's not that difficult to make a few corrections when you happen to notice something important mentioned in them.

If you have electronic charts, you're mostly out of luck when it comes to NTM updates. Some manufacturers offer trade-in programs where you can exchange older chart versions for newer, but the one I have looked at (Navionics) still charges an arm and a leg just for the update. So, one more reason to stick with paper on board.