Chart accuracy in NZ coastal waters

[Berend de Boer 2]

Having just completed my level sailing 2 course, we got introduced to nautical charts, actually quite a fascinating subject. As forum members here seems to have decades of experience sailing in NZ waters, perhaps you can give me some feedback on your experience with these charts:

 

1. Are they accurate, in the sense that you personally have never experienced a rock/reef not in there, nor know anyone who has?

 

2. Are you so convinced they are accurate that you would be happy to plot an entire course in NZ waters you haven't sailed in before, check with your GPS you are not hitting any rocks, enable the auto pilot, and go to sleep (obviously assuming every traffic moves out of your way, just a contrived example to know how much people would trust NZ charts).

 

3. How accurate are these raster charts for GPS purposes, correct within a few metres according to your experience?

 

Please feel free to refer my to other posts on this forum, but didn't find any on this subject. Thanks for any feedback!

[erice 732]

am not so experienced but

 

1 - the charts are more accurate than they've ever been   +/- 5mt? high trafficked areas around auckland, +/- 100mt? in very low? areas around the auckland islands

 

2 - they will be more accurate in the future +/-1mt? everywhere 

 

3 - the costa concordia cruise ship accident in the med. perhaps happened due to a quake? rolling a huge bolder from a rocky area into a previously clear channel.................nz is currently having quite a few quakes, so powering into something like garden cover at night at low tide may end badly even if the gps is running perfectly

 

4 - autopilots fail all the time, gps systems stumble and can be slow to get a fix

 

5 - like having abs brakes hasn't really led to a huge reduction in crashes, as people simply drove riskier, if you think you charts, autopilot and gps are infallible you are more likely to cut corners until you find they're not 

[Island Time 1,239]

NZ Charts are pretty damn good. However, No mariner worth his salt will tell you they are 100% foolproof! There are always errors and omissions, and the ocean is a dynamic place - things change over time. Basically, whatever information source, be it charts, sonar, radar, whatever, NEVER trust one information souce. Always verify with at least 2, 3 is better. One can be your eyes!

 

Dont forget one of the more dangerous objects is not on the chart - marine traffic! 

 

Yes, I do set the AP and sleep, but with radar and AIS, and only offshore.

 

Coastal I try to keep at least a mile or so (5 is better!) offshore if doing a passage, and I always follow my route thru on the largest charts available so as to be aware of anything that could be a threat. Use transits and running fixes etc to confirm your positions if Radar etc not available. This is known as pilotage, rather than navigation, nowdays taught as coastal navigation.

[Kevin McCready 83]

It's a pain in the butt but make sure you keep your paper charts updated as you've probably been taught.

[Island Time 1,239]

Yep, much easier to download the electronic ones from LINZ - already corrected

[John B 106]

I haven't looked at a paper chart except for a 'big picture' for years.

When I do they're old charts and perfectly fit for purpose. Rangitoto and Coromandel are still in the same place, and that would also be my  experience with other hard things norf too..

 The only issues I've noticed on electronic charts ( with one exception) has actually defaulted to safe by showing shallow areas where we all know we can actually go.

 

 The exception is the rock in Admin bay Motutapu, it is now named and features on updated electronic charts.

[Kevin McCready 83]

Paper charts if not updated are not fit for purpose. Buoys and beacons change and so does positioning of lights and cables and and and. If you ended up in court you'd be mincemeat trying to prove you were a competent skipper with that attitude. Sorry to be blunt but I think it needs saying.

[Berend de Boer 2]

Ah thanks guys. Yes, initially I was just going to skip printed charts altogether, but those nice big charts look pretty beautiful So bought the "Tamaki Strait and Approaches including Waiheke Island" one, just because it looks so nice. And yes, they come with a warning you need to update them (but don't tell you how, but it seems you can download the notices here).

 

But the plan is to use OpenCPN (on phone) when sailing initially, just starting with baby steps.

[John B 106]

Paper charts if not updated are not fit for purpose. Buoys and beacons change and so does positioning of lights and cables and and and. If you ended up in court you'd be mincemeat trying to prove you were a competent skipper with that attitude. Sorry to be blunt but I think it needs saying.

That information is on your electronic charts.

 signed 

Incompetent Skipper, who hasn't called coastguard in 30 years, and ( touch wood) hasn't hit anything either, but is always looking.

[MarkMT 68]

those nice big charts look pretty beautiful

 

Yep, I have Tamaki Straits and Approaches under glass on my coffee table here in Chicago. It's fit for that purpose

[Kevin McCready 83]

I know John. And when the electronics go down??

[Island Time 1,239]

What about paper - still can get wet, torn, damaged. If offshore, need sextant and tables, coastal need hand-held compass etc etc There isn't a 100% reliable system.

Modern electronics backed up by a hand-held gps or sextant and paper charts is about as good as it can be. It's very unlikely you will lose everything electrical including handhelds. A lightening strike can do that, and it can also stuff the compass magnets...

[Fish 0]

To answer the OP, yes the charts are accurate, the issues come about as to how close you want to get to pointy bits.

If you follow IT's advice and stay a mile off everything, you will be safe as houses.

 

If you want to get to within 5m of a chartered rock, you may well hit peripheral rocks. Most "uncharted" hazards are in areas where other hazards are already chartered, i.e. around known rocky reefs or rocky outcrops, there is often rocks near by that aren't shown on the charts, but the area is shown as having hazards.

 

In my experience, most issues occur not because of inaccurate charts but other more basic, human issues. i.e. trying to pass a known reef to close, mixing up tide height and chart datum etc. The classic issue is failing to check the chart as the voyage progresses, or such basic things as not keeping a proper look out. Example being team Vestas smacking into a 60 mile long island because they didn't zoom the digital chart in enough.

 

Example on a proper look out, rounding the North Eastern corner of Tiri tiri matangi in a club race, had studied chart and was rounding a long reefy outcrop on the corner of the island, had chart plotter going and believe I had allowed enough distance off the chartered danger. started thinking about sail angles for the next leg and decided it was time to start the bear away.

 

Caught a fraction of a glimpse of "something" in the water a boat length ahead (trucking at about 6 knots).

 

Didn't have time to take a second look, but threw the helm hard over and missed a rock with maybe a foot of water over it, by maybe one meter. Felt sick to my stomach afterwards, would have wrecked the boat easily at that speed and shouldn't have been trying to cut the corner.

 

The lessons there are:

A) don't sail near known dangers, and 

good pilotage (looking at stuff, having good positional awareness etc) and a proper look out trump charts, chart plotters and electronic gizmos any day. (When close in to hazards and land)

 

The charts are substantially more accurate than the human ability to make a mistake.

[erice 732]

the classic case being 2 years ago when an old salt in a classic yacht

 

was sailing to the bay of islands at night 

 

and made a mistake in identifying the bay he was in

 

ended up sailing into a very rocky area, wrecked the boat, had to be rescued

 

he thought he could take his classic, logan mullet,for the first time through the cavailli inner passage with no gps or sounder, at night with just the chart and lights on shore to guesstimate position

 

didn't work and he ran up on rocks

 

"In fact, I sailed into a minefield of small rocky islands, which just weren't clear on the map at all.

 

"I think it's a significant short-sight of the hydrographic department. The minefield was indicated to be further north; it was actually further south."

 

He also blamed a lack of lighting on the east coast of Northland for his misadventure, but conceded he did not have sonar or an electronic GPS system on his yacht.

 

"I had charts and good experience, but I hadn't actually been through that channel before."

 

http://crew.org.nz/forum/index.php/topic/11391-lucky-bugger/?hl=pickmere&do=findComment&comment=148200

 

and

 

http://www.nzherald.co.nz/northern-advocate/news/article.cfm?c_id=1503450&objectid=11561765

[Clipper 343]

If he said 'Map', im not sure he was an old salt, just in an old boat.....

[rossd 16]

My first visit to Coromandel harbour was on a dark night, what with a Cow and Calf and mussel farms, where am I?  Not sure if it was my brain or ears thought they heard waves crashing on rocks.  I to this day believe that  calf had wandered away from its mother.   

[wild violet 38]

I was recently at French Pass jetty and the brand new Garmin Gps had us on top of the hill behind it Like IT said your eyes are the best most trustworthy navigation device,Updated charts are good to sail with a few years back we sailed into Tauranga harbour at night with a dodgy motor no GPS and a chart from 1974 wasnt fun.

[Beccara 25]

If you really want to be anal about it then always compare multiple sets of data and try to work out "conflict" zones where 2 or more sets of data disagree about a hazard. The navionics webapp with sonar charts offer a great improvement in resolution but the data being "user submitted" can/will be off in places, so when compared with the LINZ charts you can get a good idea on where this may/may not be right and should let you know where you really can't cut corners

[Chloe 7]

I was recently at French Pass jetty and the brand new Garmin Gps had us on top of the hill behind it

 

Had that happen at southeast bay mayor island. On mates boat drove in dropped pick in middle off bay, then found that the gps had us about 300mts the other side of beach. Same machine had us running over a jetty in great barrier. when we where 200mtrs away. Mate replaced the gps and next trip to mayor parked in about the same place but we where still on the beach. Nothing beats your eyes.       

[John B 106]

That Cavallis business was weird right from the get go. We go through that passage and its not something I take lightly at all. Something else is going on with that one.

 

I think it goes without saying that you use multiple sources of data and information, Navionics around Auckland and the NE coast where we cruise has had to prove itself ,and it has done that to my satisfaction over the last 7 or 8 years.  Without exception it has defaulted to safe. This is typical of a few places I've seen.

 

 

I've never seen a rock unmarked ( except for the 'newly' named Admin bay one from last year  I referred to before)

 If that goes down we look at our old charts , or our tablet , or our phone , or our laptop with Open cpn.....and again it goes without saying that you make allowances for new buoys etc. No issue. None.

 The charts say we can go through that passage ^ and we have done for  several decades anyway.