What confidence do you have in your charts?

[svfinlandia]

Originally Posted by Mike OReilly

Didn't read all the references Ping, but I can easily answer your basic question: I have confidence that my charts are a general facsimile of reality.

By that I mean, I realize my charts may, or may not, be exceedingly accurate. They show some useful information about the area, which makes them useful tools. But I NEVER assume they are perfectly accurate, and NEVER place my vessel in a situation where I am blindly or solely relying on them.

I know full well that many areas I travel are poorly charted. The "source material" might be soundings that date back over 100 years in some areas. And it's quite clear some are offset from reality by up to a mile or more.

So I think I have the appropriate level of confidence in my charts. IOW, they are useful tools, but I never assume they are fully accurate. This is why in a trade, I'd rather have my depth sounder and radar over my chartplotter, or even paper charts. The former shows actual reality, while the latter displays a representation of the world which is at least two steps removed from actual world.

+1
I have found many places where my charts are not accurate.
The best example is to watch your boat sailing on land while traveling on the US Intracoastal waterway. That was probably a GPS error rather than a chart error, but many times I have seen soundings, shoals, and shorelines to be incorrect, even on a recently updated chart.

Al, S/V Finlandia

[Cynara]

We cruised in the 80s and were aware of inaccuracy then again we had no Gps so our navagation was off to. Seem to work out

[requiem]

Possibly unpopular opinion: the charts are generally OK, so long as good navigational practices are followed.

For the "children of the magenta line"... that could be an issue.

[El Pinguino]

GPS tells you - very accurately - where you are in relation to a constellation of satellites.

Your compass, your radar, your sounder, and your eyes tell you where you are in relation to the land both horizontally and vertically.

[RaymondR]

One should be mindful that the degree of trust is impacted by the local sea states and weather conditions and bottom topography and that whilst one may venture into gradually shoaling waters with mud or sand bottoms, the currents and wind likely to drive one away from a danger, it would not be prudent to trust a chart too much when approaching a reef rising from deep water with the winds, waves and currents liable to drive one onto it.

In the first instance one may exhibit the confidence of a bold and reckless rider and the second an out and out chicken.

[pbmaise]

I found in my area the most important resource was other cruisers who documented their anchorages and experience. Special call out to Valhalla!

[captrick2011]

What I usually do when plotting is to always set way point a couple of miles in the direction of deep water from my destination. Then visual,depth sounding, chart radar etc.

[Jon Hacking]

Originally Posted by pbmaise

I found in my area the most important resource was other cruisers who documented their anchorages and experience. Special call out to Valhalla!

Yes, documenting anchorages & posting them as downloadable resources is an excellent service for the cruising community.

Terry's a great old guy, but he doesn't actually go anywhere anymore, since Valhalla is parked on the hard in Davao & "isn't going in the water while [Terry's] on it." But he does aggregate anchorages that others send him, & publishes those as GPX files that can be imported into OpenCPN. A lovely service to the cruising community.

If you want more anchorages, we do much the same. We publish what amount to mini-Cruising-Guides for all the countries we visit, & we've been rattling around SE Asia since 2009. Not only do these go over general issues for each country (visas, officialdom, safety, weather, money, provisioning, fuel, phones & internet, charts, downloadable tracks, etc) but they then discuss all the anchorages that we've visited, listing lat/lons, depths, bottom, cell coverage, approach hazards, activities, & a satellite image showing our entry & exit tracks (much better than mud-maps, IMO) for each anchorage. For his own reasons, Terry has decided not to include our anchorages in his lists.

Our 19(!) Cruising Guide pages are all listed under our Cruising Info page, & include Australia, Solomon Islands, PNG, & the Philippines in the Pacific, as well as Indonesia, Malaysia, Thailand, Madagascar & several others in the Indian. Each of these document several dozen anchorages, with the Philippines covering over 100, & Indonesia almost 200. Links are provided to download our tracks & anchorages.

[Cynara]

When we were cruising we couldn't afford or carry all the charts. Once we were past certain points we traded charts with people going the other way. We ended up with an interesting mix. Even had charts from a German submarine. Our favorites were British admility charts

[ChrisJHC]

Originally Posted by requiem

Possibly unpopular opinion: the charts are generally OK, so long as good navigational practices are followed.

For the "children of the magenta line"... that could be an issue.

I think this greatly depends on where you are sailing.

There are still charts around based on surveys taken by Captain Cook!

[El Pinguino]

Originally Posted by ChrisJHC

I think this greatly depends on where you are sailing.

There are still charts around based on surveys taken by Captain Cook!

Nothing wrong with Cook's cartography. Having worked his way from Point Hicks to Torres Strait I believe his longitudes when he arrived up the top were a mere 12 miles adrift by today's reckoning.

Newfoundland Surveys (1763-1767) | James Cook 250

(Click on the chart of Newfoundland to compare Bellin, Cook and Google.)

Speaking of the top end - prior to imperial giving way to metric in the 1970's the chart of the Gulf of Carpentaria said something to the effect of 'from the work of Mathew Flinders, HMS Investigator, 1810' in the title block. When the metric chart appeared that was replaced with 'from the latest information available to the HO'. I think apart from port approaches it is still today Flinders' work.

[Cynara]

In the 70s we took navigation classes. The teacher either was the winning navigator or taught the winning navigator that won the transpac 8 times in a row. The race is every other year.
One of the other instructor when he was 16 was on a boat that was recording animals and stuff on Pacific islands. As part of that he was drawing charts of the islands and Anchorages.

He found out later these were the same charts used in WWII

[bbalan]

Originally Posted by Jim Cate

^^^^^
I just wish you had had a go at Vanuatu on your journeys, for the charts there are pretty poor. If we ever go back, we'll try to make our own, and if successful, will make t hem available as you have done.

Jim

Hi All,
MBtile charts for Vanuatu and nearly all the Pacific Island groups, the East Coast of Australia including Tasmania, several areas of the Caribbean, and all of Pacific Coast from the US border to South America are available at http://TheChartLocker.com. Most areas have four types of charts: ArcGIS satellite, Bing satellite, Google satellite, and Navionics.


Video tutorial on how to use them in OpenCPN is available as well.

All free.
Cheers,
Bruce

[davil]

thank you for sharing brucebalan

[Cynara]

No electronic charts when we went in the 80s

We mostly us us charts. We also got a few British charts and one from a Russian submarine