How to navigate new ports?

[Palarran]

Originally Posted by Mike OReilly

I was just about to respond to bmz's dangerous advice, but glad others beat me to it. Anyone who doesn't understand that a chart plotter is at least two levels removed from reality really shouldn't have one. They show you your approximate position on a chart which is an approximate representation of the world. They are wonderful tools, but I'd prioritize most of the other advice offered over primary reliance on a plotter.

I don't know if I can agree with you, so I guess I shouldn't have one. Actually I have two so maybe that's ok.

My chart plotter is freaky accurate. If it shows a rock somewhere, it's there - a single rock. Piers, marinas, nav markers, it's always been right. And as for accuracy of my location, well, it shows me backing between two finger piers, so that's pretty much as good as you can get. It's my primary navagation device and backed up by observation. I do read the pilots on many harbors I enter beforehand.

[Vasco]

Originally Posted by Palarran

I don't know if I can agree with you, so I guess I shouldn't have one. Actually I have two so maybe that's ok.

My chart plotter is freaky accurate. If it shows a rock somewhere, it's there - a single rock. Piers, marinas, nav markers, it's always been right. And as for accuracy of my location, well, it shows me backing between two finger piers, so that's pretty much as good as you can get. It's my primary navagation device and backed up by observation. I do read the pilots on many harbors I enter beforehand.

Depends greatly on the area and the electronic chart manufacturer. I dare anyone on this forum to use and rely solely Navionics electronic charts in the Bahamas. Just do a search and you will agree with me.

[boatman61]

Going up the Canakkale my CP had me sailing along a ridge a mile or so away.. or passing to the N off Cabo San Vincente.. the Corinth half a kilometre inland.. and a few other places.. the worst was just outside Soller and my GPS told me I was down near Dragonera..
Also.. How anyone can say that using a sounder and paper chart is slow and laborious only indicates to me either little or poor instructions.. a glance at a chart will show me the soundings and contours.. and setting my depth alarm will let me know when I hit the 50.. 20 or 10metre contour that I wish to follow.. what slow and laborious about that..???
This Luddite still loves the MK1 Eyeball for confirmation.
PS.. my current system use's licenced CM93 Charts.

[Palarran]

I hear ya. Many threads here over the years on chart plotter failures leading to groundings. But mine has always been accurate. C-map.

[StuM]

Originally Posted by Palarran

I don't know if I can agree with you, so I guess I shouldn't have one. Actually I have two so maybe that's ok.

My chart plotter is freaky accurate. If it shows a rock somewhere, it's there - a single rock. Piers, marinas, nav markers, it's always been right. And as for accuracy of my location, well, it shows me backing between two finger piers, so that's pretty much as good as you can get. It's my primary navagation device and backed up by observation. I do read the pilots on many harbors I enter beforehand.

I've been to one place where I was sailing through a narrow channel and the chart plotter said I was 500m inland.

And another where I was almost close enough to touch a reef marker light when the chart plotter said it was 800m away.

Just because the charts where you sail are accurately aligned to WGS84, doesn't mean they all are.

[StuM]

Originally Posted by Palarran

I hear ya. Many threads here over the years on chart plotter failures leading to groundings. But mine has always been accurate. C-map.

Doesn't matter very much whether it's C-map or any other set. They are all based on the same surveys.

"But mine has always been accurate where I have sailed" would be a more appropriate comment.

[Vasco]

The major problem with plotters and electronic charts is that you do not know their accuracy until you use them in situ. If you rely on them blindly, you might be in real trouble. It's only after you've used them that you can or cannot rely on them. Beware.

The first time I ran into this the plotter showed clear sailing dead ahead. The only problem was this little island right on the bow. Did a 180 right away. Up until then I thought it was the best thing since sliced bread.

[Mike OReilly]

Originally Posted by Vasco

The major problem with plotters and electronic charts is that you do not know their accuracy until you use them in situ. If you rely on them blindly, you might be in real trouble. It's only after you've used them that you can or cannot rely on them. Beware.

The first time I ran into this the plotter showed clear sailing dead ahead. The only problem was this little island right on the bow. Did a 180 right away. Up until then I thought it was the best thing since sliced bread.

Yes, another great example. I too have been well up on land on the plotter, while still sailing in the channel or near an island.

I’m not anti technology at all. But people really do need to understand what the plotter is actually doing, and how it’s doing it. It’s a wonderful tool. I use mine all the time, but as a secondary support to my sounder, charts, and most importantly my eyes and ears.

[odeapt]

Originally Posted by akprb

Odeapt, your question says to me that you have not had any or very little experience. I may be wrong and if so apologies.

That being said there is a mountain of experience to gain prior to "figuring out how to leave without hitting anything". Much can be gained through books, film, etc. Much from simply doing with others.

Whenever I read this type of question I wince a little. Some of the very detailed and sincere responses are spot on however miles above the OP.

This has been hashed out many times on this forum and the answers are always the same, take a course, crew, volunteer for a passage, charter, etc. Whatever you do please be prudent and know your limitations, especially if you have others aboard.

There is a reason I stay off the "Magenta Line" in the Bahamas. The chart plotter is a wonderful aid, treat it as such ;-)

Eh sorry i didnt really write the original post very carefully. I know navigating with a GPS at sea is not like a car.. i know my OP made me seem pretty oblivious. I understand how plotting a course on a paper chart is done, and know that a GPS wont just give you directions.

I do not want to rely on my eyes to see a reef before I hit it, and a depth sounder will be too late.

Im really just trying to figure out how i would plan this trip from the west side of the island to the south end. It wouldnt be for several months so i definitely have time to learn. I work on a submarine so ill be able to learn a lot from friends.

I will probably end up hiring somebody to move the boat this time and give me lessons at the same time, but I want to start figuring this out now.

[boatman61]

Originally Posted by odeapt

Eh sorry i didnt really write the original post very carefully. I know navigating with a GPS at sea is not like a car.. i know my OP made me seem pretty oblivious. I understand how plotting a course on a paper chart is done, and know that a GPS wont just give you directions.

Im really just trying to figure out how i would plan this trip from the west side of the island to the south end. It wouldnt be for several months so i definitely have time to learn. I work on a submarine so ill be able to learn a lot from friends.

Well we're all suffering winter boredom.. give us a where to where and we'll take a look and maybe can be of help.
Be interesting to see how many agree on routing..

[SV DestinyAscen]

Chart plotter can plot your specific location very accurately. The map data it relies ok however varies wildly and unexpectedly.

For example if you're relying on certain charts for the south pacific, except for French and New Zealand surveys that are more recent, the rest probably dates back to Captain Cook. If you don't believe me just compare Google earth satellite photography with charts and you'll notice variation.

The good news is that with reasonable prudence you generally know where charts are less reliable. Folks who claim they're perfect probably haven't left US surveyed waters.

If you use CM93 you'll find that their focus on commercial shipping gives you a lot of good data on more busy ports and recommended channels in more hazardous waters. But go to regions where there's limited commercial shipping and CM93 itself will tell you it lacks sufficient detail for navigation disclaimer.

Even navionics isn't great - I recently looked up a bridge by Nagasaki, navionics says it's underconstruction . I know it's been done for at least two years.

[Palarran]

It's interesting how many of you have this plotting error. For me, never.

The issue of being under zoomed though - did have that once where at 16 nm zoom it didn't show the reef but at 8 it did. For me that's where you really need to know how to use your specific plotter

[odeapt]

Originally Posted by boatman61

Well we're all suffering winter boredom.. give us a where to where and we'll take a look and maybe can be of help.
Be interesting to see how many agree on routing..

I would certainly not want to waste anyones time with that, although I do appreciate the offer.

[StuM]

Originally Posted by Palarran

It's interesting how many of you have this plotting error. For me, never.

It's interesting how people who sail in more remote areas appreciate that charts in many parts of the world are based on old and inaccurate base lines and limited surveys and that plotter displays reflect those charts: while those who have only sailed in more "civilised" areas find it hard to comprehend that the whole world hasn't been surveyed in detail on the WGS86 geoid and tend to put more trust on what their plotter tells them.

[DumnMad]

So are some of you suggesting that Hawaiian charts are so inaccurate and out of date that Navionics will lead you onto rocks??