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Old 09-06-2010, 20:01   #16
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Quote:
Originally Posted by MarkJ View Post
2 Screen captuers below of the location I suppose Airwego hit the reef.
<snip>
But now look at the Mark I have put in on the chart. Now look at the Google Earth image and see the SAME L&L is 1,000 meters to sea!!!!!!!!!!!!!!!!!!!!!!!!
I wonder if this is a case of the wrong datum (ellipsoid) being used ? Wrong as in different for Google Earth and your chart plotter.

That raises the question of how Google Earth handles the different datums needed around the world and why can't chart plotters do the same ?



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Old 09-06-2010, 22:33   #17
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That is horrible to hear and even worse the cost of pulling it off the reef only to sink again

Glad they are okay and hope they make it back on the water in a timely manner.
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Old 14-06-2010, 03:12   #18
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Mark,

We were lucky enough to meet an ex navy sub captain when we were heading out that way years ago.

He gave us a very important bit of advice which we never forgot.

Don't rely on GPS positions! The reefs and islands are not where they are plotted on charts in most cases.

He did however point out that in relation to the islands the reefs were always were they were supposed to be, therefore is you had radar, you found the island then the reef.

Also Mark, you truly summed up the photo.

Nothing sadder than seeing a photo of a yacht on a reef.

End of yacht and end of a dream.

Good to hear that they are Ok but I feel for them.

Cheers
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Old 14-06-2010, 21:01   #19
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We were very saddened to learn of the loss of S/V Airwego. We know Mike & Cindy, as well as Alan & Kristen on S/V Charisma (the boat they were following through the pass) and Sally & Glen on S/V The Dorothy Marie (the blog where this was first posted). We understood from Alan that Mike & Cindy did have insurance, so are surprised to learn differently from Bill Streep's posting above.

This loss strengthened our decision to continue carrying insurance. Every year we debate with ourselves whether the insurance is worth the high premiums. These days, unless it happens in open ocean, you can pretty much count on having to pay for environmental damage anywhere your boat is lost. That cost is almost certainly going to be much more than an annual insurance premium.

Very sorry to learn that Mike & Cindy are facing such expenses at a time when they must be traumatized by the loss of their boat/home.

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Old 14-06-2010, 21:50   #20
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Mike and Cindy reiterated the importance of carrying insurance, in spite of the costs. On top of their loss, it would likely have covered the Samoa fees as well. In their case, they couldn't get out of Samoa before paying the costs.
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Old 14-06-2010, 22:28   #21
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Mark,

Your images of Google Earth and the chart are interesting. I plotted the waypoint on our latest C-map charts using Maxsea as the viewer and there is a difference from Google Earth, just as you illustrate. To me the most interesting thing is that there is a significant difference in the latitude more so than the longitude. That is unusual. Most of the differences we have encountered between true GPS waypoints and charts have been longitudinal errors. Which makes sense because most charts were done during days of sextants. The old hydrographers tended to be fairly accurate with latitude but were often off on the longitude.

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Old 14-06-2010, 22:44   #22
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I was always uncomfortable going through passes that were new to me when I was in the South Pacific. The charts frequently are wrong, and you need local knowledge to safely navigate through some passes, and in others, you have to get the time of day right so that there is slack tide. If there is a sea coming in from the wrong direction, you can't go safely in as well.

I always was glad to have two engines running on Exit Only when going through passes. If one engine failed, we still had a chance with the second engine. (I never had an engine failure going through a pass). We usually had someone in the first level of spreaders as well. We always went through slowly until we were 100 percent sure of what was happening.

Fiji is also tricky when navigating passes. The international dateline passes through Taveuni, and on one side of the dateline, the charts need to be corrected to the east, and on the other side of the dateline, the charts need to be corrected to the west when using the charts from the Fiji government. We were very careful and triple checked our waypoints and our charting to stay out of trouble in that part of the South Pacific.

Sorry to hear about the loss in Samoa.

Bummer.
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Old 14-06-2010, 23:42   #23
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I think the Pacific islands are the most tricky we have seen and that some mistakes are very very easy to see how they could happen. Sometimes it just looks like luck or bad luck. I think this one was just bad luck.

We are fortunate that we don't mind not going in if unsure. We both prefer to stand off for the night, or go to another port, anchorage etc.

When I say 'we don't mind' its an interesting thing that we seem more at home at sea on our boat that some others. Some folks, in a general sort of way, much prefer to get to anchor than stay at sea.

On the Nav side. When we were in Tonga we had a bad situation that I pushed ourselves a bit... getting into an anchorage behind a island where the approach have a long reef. The reef was a lee shore, the wind was picking up, its was 6.30 pm, charts definitely inaccurate, hand drawn photocopied Sunsail map.... I knew I was pushing it a bit. But I used Google Earth (not connected to the internet - I have paid for the premium service thats now free) and found Google Earth to be absolutely perfectly accurate.

No, I don't rely on Google Earth, but each time I connect it to the GPS it is absolutely 100% perfect in position. The comments by Get-a-Life are correct, one must be able to eyeball all the way in. But I like 2 things, my eyes plus something aditional to tell me my eyes arn't lying

I had a couple of screen captures to show how accurate Google Earth is... but do you think I can find them on this computer?

Nic and I discussed the Airwego situation and we have decided to make sure we only go into places which are a bit easier than this entrance. If we have to miss idyllic locales then so be it.

The Chart shows 70 meter wide straight channel but Google Earth shows half that with white water! Its only 35 meters of dog leg channel without white water. Thats too narrow for me.

I hope Mike and Cindy are feeling better about it all now. The very least is for us all to learn a little more about the tricky nature of our cruising life


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Old 14-06-2010, 23:49   #24
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Mark,

Quote:
Originally Posted by MarkJ View Post
... I used Google Earth (not connected to the internet - I have paid for the premium service thats now free) ...
Do you mean that you have all the data downloaded or how do you use it without being connected ?

Thanks,


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Old 15-06-2010, 00:29   #25
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Mark,
Do you mean that you have all the data downloaded or how do you use it without being connected ?
-Sven

Hi Sven,

When connected to the internet I go over all the areas I will be cruising in Google Earth. These images are automaticaly cached by Google Earth.
Then when DISconected from the net Open Google eart Click NO when it asks you if there is a problem. Google Earth will then open and you can view those areas in the Cache.

You can better organise the cache but downloading simeple programs to help (some cost money) or work out how to do it yourself.

Google earth still lets you plug your GPS in whilst not connected to the net


It really is excellent!


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Old 15-06-2010, 00:34   #26
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Mark,

Sorry for the thread drift but I'll definitely have to look into that caching. I had assumed the caching was lost when you shut down. Very interesting !

Thanks,



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Old 15-06-2010, 01:14   #27
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Back to the issue of Google Earth displaying this waypoint at a different location than the C-map charts. In this particular instance, it appears that the C-map charts more accurately place the waypoint than does Google Earth. The point obviously is not 1,000 meters out to sea as is shown on Google Earth. They clipped the edge of the reef entering the channel, which is very close to where C-map displays this waypoint. However, I do think having aerial views from Google Earth would be of great benefit when entering passes such as this.

As I understand it, we would have to save the Google Earth images for our planned route while we are connected to the internet and then utilize these images on our computer when not connected to the internet. I don't think we can actually access Google Earth when not connected to the internet. If my understanding is incorrect, please enlighten me.

Judy
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Old 15-06-2010, 04:18   #28
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Very sorry to hear of the loss. We cannot know all the details as we weren't there, however, there may be some value to be had from trying to learn from others' mistakes.

Cruising the South Pacific taught me to rely on the Mk1 eyeball more than the charts. We had many seamap/maxsea plots going over dry land as it was shown on the electronic charts. I strongly agree with the advice given by the submarine skipper. Once you've located the landmarks with your eyes, you can use traditional navigation techniques to work out where the reefs are relative to those points. In some cases you can totally ignore the lat/long of the passes, but this should be no surprise to experienced cruisers. If you're unsure, don't travel through the difficult area under difficult conditions - eg. at night, with a heavy sea etc...

When entering potentially difficult passes we always waited for slack water or a slight following current, and would rather remain at sea than risk difficult sea conditions to get through.

A friend of ours insisted on navigating into Tahiti past the airport using his GPS rather than his eyes. Unsurprisingly, he ran aground, but thankfully no harm done. This was while his crew were on the bow telling him he was outside the marked channel. Remember that the vast majority of locals in these places don't use GPS or charts, but they do use landmarks and buoys.
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Old 15-06-2010, 06:15   #29
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I too need to know more about GE caching.

Here is a photo (I hope) of the entrance to Francois, Newfoundland.

There was very heavy fog, I found the buoy on the radar and came in that way watching my offset from charted path. The problem with radar is that you can see a headland, but you can't always tell WHICH headland it is.
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Old 15-06-2010, 06:52   #30
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My skipper training tells me that if I found myself in fog, I should try and get away from dangers like land, headlands, channels etc... the idea of trying to go down a channel in this situation is completely counter-intuitive to me.
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