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Old 01-08-2017, 19:23   #196
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

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I thought this was interesting and looked up the charts. There's a significant depth change from 2000 meters to fewer than 200 in about 4 nm. I would be inclined to follow the surveyed 2000 meter depth around the island until I'm able to get to the right bearing for the recommended track that larger ships use, before I would begin really approaching closer.

It is a night approach at a new island - one nm off the pass the depth is still 500m. I'd really have to be sure and committed that I can hold the course before I'll commit. If I can't do it half a nm out I'm declaring no go and going around.
How would you navigate to stay in the 2000m waters? I don't have anything onboard that reliably will measure 200m depths, and that's with two depth sounders.
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Old 01-08-2017, 19:53   #197
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

I'd just use the chart to estimate depth. Key is to avoid confused wave conditions.
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Old 01-08-2017, 20:15   #198
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

Part of the issue here there was an SW swell running, but the wind was out of the ene.

On all the fringe reef islands we've seen, the waves break perpendicularly onto the reef, at the very end, they have refracted around.

Where the bottoms come up fast, the waves hump up. One of the reasons to stay further off where the bottom comes up fast is to stay where the waves are "normal", even including the ones at the tails of the averaged wave heights. It doesn't show as well on the Navionics chart as on the real chart, but you can see the contour lines are almost right on top of each other. That tells you it is a sudden change of depth.

Obviously from this discussion it is not wise to follow contour lines close to reefs; and nor, is it a great idea to follow the continental shelf depth contour line, either. You get stuck there with strong wind against the continental current, and just like seamounts, it is a place best avoided, especially in rough weather.

How close you are comfortable with being also depends on whether it is rock, hard coral, hard mud, soft mud, hard sand, or medium sand. That is why charts have notations as to what the bottoms are, to inform you.

Cheers, guys,

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Old 01-08-2017, 21:07   #199
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

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I'd just use the chart to estimate depth. Key is to avoid confused wave conditions.
It is the chart that was being doubted here. There really are places where chart elements are correct except their positions are shifted significant distances - lime in miles. Staying in deep water makes sense. After you use charts in a location you get a feel for how trustworthy they are. Then you make the judgement call of staying clear by X miles, where X is the navigators judgement for the area, time of day and general conditions.
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Old 01-08-2017, 21:19   #200
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

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It is the chart that was being doubted here. There really are places where chart elements are correct except their positions are shifted significant distances - lime in miles. Staying in deep water makes sense. After you use charts in a location you get a feel for how trustworthy they are. Then you make the judgement call of staying clear by X miles, where X is the navigators judgement for the area, time of day and general conditions.

Indeed. Which is why I like 2000m.
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Old 02-08-2017, 04:01   #201
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

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Why so far. I expected 400m (1/4 mile).
that's why insurance premiums are what they are ("premium")
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Old 02-08-2017, 07:03   #202
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

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There is an interesting tension on a cruising boat (and perhaps more broadly in life). If you are not paranoid and careful enough you will lose your boat, BUT if you are too paranoid and careful you will never do anything interesting and challenging.

Most cruising couples cycle thru this spectrum. They start out on the careful end, then they build miles and everything is going well and they get more "adventurous" / less careful, then they make a mistake or have some bad luck and get slapped down hard, and they cycle back to careful.

Even after two rtw's we still cycled thru that continuum. One of the more difficult times Beth and I had was the first time we were in chile. Before that she had been the careful prudent one and I the adventurous risk taker and we had sort of reached a good balanced decision making process. But when we got to chile it was initially a bit beyond my comfort level (and I had just made a bad mistake in Iceland which wrecked my confidence) and I wanted to be extra careful, while she had sailed thousands of miles to this special place and wanted to go everywhere and see everything and somehow felt very comfortable. The reversed roles sort of threw us for a loop for a while.
This actually came up in a discussion tonight. I was a better cruiser when I started than I was four years later, hitting a reef taught me how dangerous complacency is, and that a little fear is healthy, fortunately the lesson wasn't costly.
I now try to be concious of complacency creeping in ,particularly when tired.
Another good point Evans mentioned was knowing when being alert is important and when its not.
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Old 02-08-2017, 07:05   #203
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

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Why so far. I expected 400m (1/4 mile).
Im with Jim, being conservative wont kill you. What's that saying " there's old sailors and bold sailors, but no old bold sailors".
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Old 02-08-2017, 07:21   #204
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

when sailing from the Marquesas to the Tuamotus in the "sextant-days" we'd plan for an arrival just after full moon, kept 15 miles off (according to our navigation) & I spent most of the last night before landfall taking starsights (& of course working them out). served us well on rtw 1 & 2!
I wouldn't choose to pass within 1/4nm of the southern tip of Huahine-reef in broad daylight & under perfect conditions - what would it be for?
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Old 02-08-2017, 07:36   #205
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

"curiosity killed the cat"
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Old 02-08-2017, 08:58   #206
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

The other possibility for this "navigational error" may be to do with the chart plotter and not the charts. We recently had our Raymarine E125 replaced under warranty and almost got into trouble a few days later when we discovered a very serious issue with the replacement unit. The boat curser had frozen in position and was not updating on the plotter despite the GPS Co-ordinates still updating. I only realised because I was navigating a reef entrance and what my eyes were seeing was not matching what the chart plotter was telling me. If I was offshore this error would be almost impossible to pick up without other features like AIS targets to reference. After discovering this fault we found it was happening randomly every other day and the only way to unfreeze and update the vessel position was to switch to another screen item like radar and then back to the plotter. Raymarine have been very quiet about this issue despite several emails from me, I recently sent the unit back and the issue is yet to be resolved. If this is what happened in this scenario I think there is absolutely a case for going after Raymarine, disclaimers or not the unit is not performing how it should. I was super angry when I first discovered this issue because it could so easily result in losing my boat in the dark.
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Old 02-08-2017, 09:38   #207
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

"... this error would be almost impossible to pick up..."
maybe with DR on a paperchart?

imho offshore not keeping a DR on a paperchart (like on Moorea-Huahine) is not a "navigational error", but plain idiocy, incompetence & ineptitude & simply inexcusable & irresponsible towards the people entrusted to ones "care"!
(but what do I know after 3 rtws...)
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Old 02-08-2017, 09:58   #208
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

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"... this error would be almost impossible to pick up..."
maybe with DR on a paperchart?

imho offshore not keeping a DR on a paperchart (like on Moorea-Huahine) is not a "navigational error", but plain idiocy, incompetence & ineptitude & simply inexcusable & irresponsible towards the people entrusted to ones "care"!
(but what do I know after 3 rtws...)
You are describing 99% of cruisers that I've met (me included). I write our co-ordinates in the log every hour (for back-up) but don't plot them on the paper chart, why would I when my plotter is supposed to do a much better job updated every second? This Raymarine issue is something I had never seen or heard about before, even so I keep an iPad running at the helm station usually with Bluecharts to reference and compare the Navionics charts. So far the iPad has sadly been more reliable than the 10K plotter. I guess that's the difference between old school and new school sailors, still I bet more old school sailors ended on the rocks with navigational mistakes.
Anyway I was merely highlighting a feasible reason for the mistake based on my own recent experience.
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Old 02-08-2017, 10:01   #209
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

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"... this error would be almost impossible to pick up..."
maybe with DR on a paperchart?

imho offshore not keeping a DR on a paperchart (like on Moorea-Huahine) is not a "navigational error", but plain idiocy, incompetence & ineptitude & simply inexcusable & irresponsible towards the people entrusted to ones "care"!
(but what do I know after 3 rtws...)
Well how? If the GPS position was updating flawlessly but the chart didn't there's no way to see the error in openwater DR or not nor plotting the positions on paper..
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Old 02-08-2017, 10:16   #210
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Re: Leopard 46 lost in French Polynesia - stunning rescue pictures

...our understanding of DR seems to differ...:
"...advancing that position based upon known or estimated speeds over elapsed time and course..."
but maybe you people don't have logs any more...
"...more old school sailors ended on the rocks...": restricted to "old-school methods" most of those "new-school"-"navigators" wouldn't get far!
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