How Do I Update My Charts for Variation/Declination?

[Jim Cate]

Re the discussion of "how close to a given heading can you steer" issues:

My observation of how I navigate and by discussion of how many of our cruising friends do so indicates that this question is not all that relevant.

Once out of traffic, where constant vigilance and frequent course changes are required, most cruisers will set an a/p or wind vane to steer the boat. They will typically select a destination or way point some distance ahead, and from a chart or a plotter, determine a course to steer. Careful folks will monitor the GPS derived COG for a while and make corrections until CTS and COG are well matched. Then they relax and let the device of choice steer the boat. After a while, they will plot (paper or plotter) their current position and determine a new CTS (possibly unchanged) and reset the steering device as needed. This is repeated until the waypoint or destination is reached.

None of the above requires staring at a swinging compass card and wondering if one is within 2 or 4 or whatever degrees of the CTS. This may not be what the traditional sailors advocate, nor what YRA teaches, but it is what happens on a typical short handed cruising boat. Some trusting folks even rely upon the a/p to automatically do this procedure for them, for when you set the a/p to follow a route, it does exactly the same thing, only more frequently, monitoring XTE and seeking a course to minimize it.

There are a few special places in the world where other methods are advantageous, places like cross-channel passages between England and the continent. The strong tidal currents running roughly athwartships your course, coupled with the very detailed tidal information that is available there allow one to calculate and then steer a constant heading all the way across. When done correctly, there are advantages to this scheme, and it does require careful steering to a set course, with no intermediate corrections applied. The situation is pretty unusual, especially with regard to the quality of the info available, and does not often appear in the rest of the cruising world.

For those still practicing celestial navigation, having good knowledge of variation and deviation is more important, for you do not have the convenience of an accurate COG to feed into your DR... which is all you have between fixes. I must admit that when I made passages with celestial, I was careful to swing the compass prior to departure, and to check the age of the variation figures on the chart... and landfall was a lot more exciting than it is today!

Jim

[toddster8]

Oh... Yeah, I've heard of people who cross the bar that way. They're called "shipwreck victims."

[Jim Cate]

Crossing the bar is very dangerous, especially when the bartender has a billy club...

Jim

[wolfesmy]

For changing True to Magnetic use the following:
TVMDCSE
True Virtue Makes Dull Company Saturday Evening
True Variation Magnetic Deviation Compass Subtract East
For Changing Magnetic to True
CDMVTAE
Can Dead Men Vote Twice At Easter
Compass Deviation Magnetic Variation True Add East

Use the appropriate correction values for chart variation and compass deviation and add or subtract east values as required.

Hope that helps or at least adds to your confusion. Lots of good information on the net or take a coastal navigation course. Well wort the price of admission.
Another good source is "Davis Quick Reference Coastal Piloting" for about $12 US they are a great condensed source of information.

[wolfesmy]

Jim Cate makes a point, however I always maintain at least 2 forms of navigation when offshore, and often coastal cruising as well. Instruments can fail and autohelms can break down and you have to steer by compass. It's great that everyone is using GPS as thier primary means of navigation but where are you when the system goes down. At the very least note your Lat and Long every hr. So that if you ever need help you can provide reasonable information.

[meirriba]

Originally Posted by wolfesmy

Jim Cate makes a point, however I always maintain at least 2 forms of navigation when offshore, and often coastal cruising as well. Instruments can fail and autohelms can break down and you have to steer by compass. It's great that everyone is using GPS as thier primary means of navigation but where are you when the system goes down. At the very least note your Lat and Long every hr. So that if you ever need help you can provide reasonable information.

As two 2 forms of navigation: I do use two independent ELECTRONIC systems. One the boat's MFD with it's maps, the second is an OpenCPN system on a laptop with differently sourced charts.
I have stopped the automatic route function of the AP (automatic change of course when arriving at a waypoint) - it seems to me too much freedom for the machinery. I would like the watch person to be aware of any course amendment.
We note position every so often in a paper log book as an extra to the automatic registration by the MFD (track function).
If AP breaks down, we can helm with the MFD in sight of the helmperson.
As to GPS breaking down - there are at least 4 units onboard.
World GPS system going down - seems rather apocalyptic nowadays - all shipping, airlines, taxi fleets, UPS fleets etc. will stop...

[Paul L]

Originally Posted by meirriba

.........
If AP breaks down, we can helm with the MFD in sight of the helmperson.
As to GPS breaking down - there are at least 4 units onboard.
World GPS system going down - seems rather apocalyptic nowadays - all shipping, airlines, taxi fleets, UPS fleets etc. will stop...

If you are unfortunate enough to find yourself in an area where a major power is involved in a military operation, you may find the civilian GPS signal jammed for a period of time. You can decide if that is apocalyptic or not

[meirriba]

Originally Posted by Paul L

If you are unfortunate enough to find yourself in an area where a major power is involved in a military operation, you may find the civilian GPS signal jammed for a period of time. You can decide if that is apocalyptic or not

It is...
Why should I sail in such a place if I can avoid it? And if I can't I am sure that the navy force on site will show me where to go.

[Paul L]

Originally Posted by meirriba

It is...
Why should I sail in such a place if I can avoid it? And if I can't I am sure that the navy force on site will show me where to go.

Says the man confidently with his boat in Turkey. I wouldn't count on escorting you to saftey as being a high priority for any invading force.

Can you imagination cruisers in Cyprus or Grenada during a military operation - doesn't take much because it's already happened.

[belizesailor]

Originally Posted by Paul L

If you are unfortunate enough to find yourself in an area where a major power is involved in a military operation, you may find the civilian GPS signal jammed for a period of time. You can decide if that is apocalyptic or not

Have had that happen. Wasn't apocolyptic unless you were on the receiving end of Operation Desert Storm.

[Bigjim]

Originally Posted by nigel1

Best way to correct charts that old is to replace them with new charts.

This is not as foolproof as you might think. New charts may still be several years old when you buy them. I was a Navigator in the US Navy. We would pick up charts all the time whenever we steamed to different locations.

The "new" charts were not always up to date. There just isn't a reason to update a bunch of charts and throw away all the old ones. Maybe they do it differently today.

But we would pull out a chart and then grab the various Coast Guard reports for each of the charts that listed the changes to the chart: new buoys, wrecks, deletions, etc. Often, we spent hours or days manually updating a chart for a specific area.

Hundreds of charts of each area are printed all at once. Depending on the source you are buying them from, don't count on them being up to date. Often, there will be a date on the Chart indicating the last time it was updated.

[Bigjim]

When close to land, keep a close lookout for lighthouses, or lighted buoys. Charts will usually indicate the period of the oscillation. When far offshore, taking sun lines and keep a dead reckoning track on the chart can be a real boon.

I've found landfall can be very deceptive. Nothing looks like you expect it the first time you arrive at a destination. I recommend researching and reading up on harbor notes and such before arriving at a destination. The more you know about the harbor or approach the better.

I had a handheld bearing compass to take bearing lines for navigation. Didn't travel to many unknown destinations, but being prepared is the first step.

Today, you can even use Google maps or satellite imagery before traveling to a place. Copy the screen shots and such and save them to your laptop. Identifying the best anchorages or docking facilities beforehand is crucial.

[nigel1]

I thought the US had a similar system as the UK, with corrections to charts published weekly. On the ships I have been on, all charts are kept corrected, and when a new edition is published, the new chart is purchased, and the old one usually ends up as jointing material for the engineers.

Trouble is with really old charts not all corrections will be available. If the chart has been replaced with a new edition, not all the corrections incorporated in the new edition will published as separate corrections

If Admiralty charts are purchased from an approved supplier, they will just about be up to date (the approved supplier is obliged to correct the charts).
Nowadays, most Admiralty charts are printed on demand, and will be up to date.

I'd rather ditch a 20 year old chart and purchase the new up to date one, cost over a few years is not much.

Originally Posted by Bigjim

This is not as foolproof as you might think. New charts may still be several years old when you buy them. I was a Navigator in the US Navy. We would pick up charts all the time whenever we steamed to different locations.

The "new" charts were not always up to date. There just isn't a reason to update a bunch of charts and throw away all the old ones. Maybe they do it differently today.

But we would pull out a chart and then grab the various Coast Guard reports for each of the charts that listed the changes to the chart: new buoys, wrecks, deletions, etc. Often, we spent hours or days manually updating a chart for a specific area.

Hundreds of charts of each area are printed all at once. Depending on the source you are buying them from, don't count on them being up to date. Often, there will be a date on the Chart indicating the last time it was updated.

[Bigjim]

The US Coast Guard reports changes to nautical charts. These were made monthly in the past. Periodic updates were published more frequently when necessary. We would go the Navy office that kept the charts. Local area charts were maintained by the personnel in the office. But there are just way too many charts to keep them all up to date. On demand printing would be ideal. But I'm not sure that's available everywhere. Most color ink printers are water soluble. This would be a bad thing on a boat. So, I'm hoping that they are using toner or waterproof ink.

The first step in all navigation is to know where you are going and what track you intend to take. Sailboats can't always approach a destination from a specific direction. We move with the wind. I remember reading about how John Adams traveled to Europe the first time and literally waited a week a few miles away from home for the wind to change direction.

Electronics are unparalleled for accuracy and convenience. But relying solely on them is foolish. As a navigator, we were drilled to maintain a dead reckoning track. You draw the track and place your assumed position on it and placed marks for where you should be at any time in the future. These marks were constantly updated as we progressed along the track. We made lists of lights and other salient markers when available to confirm all these assumptions. We even advanced various bearings when made using our assumed speed and course.

My fear was having only one method of navigation when close to land. We read many stories of ships missing Hawaii entirely in the old days when their course was one or two degrees off.

[Bigjim]

Here's an example of relying on one type of navigation: In the 70s I was in the US Navy and we were steaming up to Seattle from San Diego. We relied on radar for most navigation chores. This was ideal for Southern California. The coast is rocky and usually has a high bluff along the shore.

When you get north of San Francisco, the shore starts to get lower and softer. When you get to Oregon and Washington the shore is low and slopes gradually back to the mountains. When you are 100 miles out at sea, you can't see any of the coast on radar. Only mountain tops. Our Omega and Loran systems never functioned. And up north there was a lot of overcast.

Luckily, we were well out to sea and no concerns for grounding. But it was a tense day or two. We'd shoot sun lines during the day and LAN to establish latitude. Advancing the sun lines during the day to establish a rough fix. Sometimes we'd go into CIC to use the air search radar.

The most fun I had was shooting stars at dusk and working out the celestial lines from several stars and even throwing in a Moon shot. It was a great sense of pride when I plotted the lines and got a relatively small triangle on the chart.