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Old 03-05-2012, 18:32   #91
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Re: Sad News Again Off Mexico

sabray,

Each of us has a very private list of things we've done while cruising, that we'll never tell to anyone. I almost lost my life things. the passage from hell things. For me I could have been killed three times and I almost lost my boat 6 times.
Then there are the outright stupid things, the embarassing things, the times the entire marina pointed at you and laughed things. The times that the other boats at the anchorage came to your assitanence and saved your sorry behind and your boat.
The great thing about this CF is that we share and discuss these stories.

But there are still stupid things I've done that I seldom remind myselj of, let alone tell anybody else about. One of the perks of sailing singlehanded.
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Old 03-05-2012, 19:38   #92
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sabray,

Each of us has a very private list of things we've done while cruising, that we'll never tell to anyone. I almost lost my life things. the passage from hell things. For me I could have been killed three times and I almost lost my boat 6 times.
Then there are the outright stupid things, the embarassing things, the times the entire marina pointed at you and laughed things. The times that the other boats at the anchorage came to your assitanence and saved your sorry behind and your boat.
The great thing about this CF is that we share and discuss these stories.

But there are still stupid things I've done that I seldom remind myselj of, let alone tell anybody else about. One of the perks of sailing singlehanded.
Amen to that. The biggest risk is hubris. And in reading this forum for the last several years the most common manifestation of that is, "I am a superior sailor therefore I can do things no others can."

I suffer from this as much as the next person but I like to think that my fears keep my hubris in check. That and the fact I love to learn. I know that I do better collaboratively than I do making solo decisions. Even newbies offer insight that I try to take advantage of. Perhaps their higher level of fear or uncertainty acts as a check and balance to my own decision making. I like to think so.
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Old 03-05-2012, 19:42   #93
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Re: Sad News Again Off Mexico

Have they found the skipper yet? Maybe he went over an hour earlier while on solo watch and the boat auto-ed on...and on. Any number of alternatives.

But another reminder to always tether, even if that wasn't a factor this time.

BTW, a query to those with chartplotters: surely setting a leg through dry land sets of alarms and strobe light warnings?
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Old 03-05-2012, 20:19   #94
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Have they found the skipper yet? Maybe he went over an hour earlier while on solo watch and the boat auto-ed on...and on. Any number of alternatives.

But another reminder to always tether, even if that wasn't a factor this time.

BTW, a query to those with chartplotters: surely setting a leg through dry land sets of alarms and strobe light warnings?
No it doesn't. GPS will allow airplanes to fly through mountains, cars to cross bays without bridges and boats to sail in deserts.

That is the whole point of these gps nav threads.
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Old 03-05-2012, 21:40   #95
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Re: Sad News Again Off Mexico

Perhaps Zee can correct my recollection if it is wrong as she is familiar with the Islands but I recall on deliveries headed south, I would stand off North Coronado Island about 1-2 miles in the lee but stay off the south island 2-3 miles due to the foul ground and the navy installation on the South Island. The western side of both North and South Island was considered dangerous within 5 miles due to sneaker waves and surf around the points. From South Island course would take us outside the submarine berth off Rosarita Beach which is well lit.
Sailing south, much would depend upon the wind strength but heading outside added considerable distance so you would have to be certain you could make up the time.
Most take the inside between the islands and the mainland of Mexico as I recall but you won't know until you are just north of North Coronado whether it is worth the risk to head outside for stronger winds.
I know that fishing boats hang more around south Island because it is higher and more protected that the North Island.
Not sure we will ever know the answer to this tragic mystery... Capt Phil
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Old 03-05-2012, 21:55   #96
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Re: Sad News Again Off Mexico

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dennis--the only fault with your paragraph is that the coronado islands are visible from san diego undermost all circumstances. t
At 0130 in the morning???

I know that things are different up there in the northern hemisphere, but it tends to be bloody dark at that hour down here!

One can only guess at why they were on the recorded course, but there is pretty good evidence that they were in fact headed right at the island. If motoring, the sound of surf may have been obscured, and the island, being unlit, might be pretty hard to see end-on in the dark of night.

It will be interesting to see if they can find the keel...

The presence of a large merchantman that close to the island seems unlikely, but how about a big trawler? Others have pointed out that various fishermen hang out in the area, and a collision with such could have disabled the vessel, leading to it's being destroyed in the surf. We know from past experience that fishermen do not always do the right thing under such circumstances.

I suspect that it will remain a mystery and a source of conjecture for all time!

Cheers,

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Old 03-05-2012, 22:14   #97
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Unless the spot time and location are way off the boat reports consistent progress and course straight at the island. At 0136 it's in or damn near the surf of the island. Unlikely it finds a boat to collide with that close. Less
Likely they would have planned that course deliberately. Their speed is consistent and direction consistent. If they were able and aware they would have changed course and speed much earlier. This suggests that they were unaware or unable to recognize the danger. I really can't see how this can involve a second vessel. Really don't like that merchant seamen and fishermen are wrongly being subjected to bad unwarranted suspicion. Because the race organization did not disclose what they should have known and the press was lazy and falsely reported the event as a collision.
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Old 03-05-2012, 22:34   #98
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Re: Sad News Again Off Mexico

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No it doesn't. GPS will allow airplanes to fly through mountains, cars to cross bays without bridges and boats to sail in deserts. That is the whole point of of these gps nav threads.
If I draw a leg of a course between waypoints on a paper chart and find that it passes through land, then not surprisingly a little strobe alert fires up in my head and I rethink my course.

So are you saying there is not, or ought not to be, or cannot be, a function on electronic charts that sets off a similar alert in similar circumstances?
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Old 03-05-2012, 23:06   #99
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Originally Posted by At sea

If I draw a leg of a course between waypoints on a paper chart and find that it passes through land, then not surprisingly a little strobe alert fires up in my head and I rethink my course.

So are you saying there is not, or ought not to be, or cannot be, a function on electronic charts that sets off a similar alert in similar circumstances?
GPS simply triangulates a position from the satellites based on the time the signals arrive at the gps. Depending on the number of signals available this position is plotted as 2d or 3d with increasing accuracy as a higher number of singals is received.

The gps is basically oblivious to terrain. It only knows about time.

Plotter makers add chart data to the gps position. All chart data relies on some sort of Datum. Different Datum are chosen for different reasons.

It would not be unreasonable or impossible to integrate the chart data with the course data and provide a method of warning the navigator that intended course travels over land. It would require a level of computing power and chart data not currently included in most consumer level electrronics.

I guess one way to look at it is like using a laser pointer and a slide. You can point the laser pointer at the wall - the location of the pointer is meaningless. You project a slide of a chart and can pinpoint a harbor projected on the wall. Change slides without moving the pointer and the location of the laser dot becomes meaningless.

Most chart data is "flat" data. It is a slide projected onto you plotter. This allows the chart data to be fairly small in size. Imagine if you need the 3d data for every point on earth in say 1 square foot increments in order for the plotter software to know the altitude of the features on the chart. That's a lot of data.

And of course when using a plotter to plot a course the human light should definitely go off in your head if the magenta line goes across an island.
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Old 03-05-2012, 23:30   #100
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Re: Sad News Again Off Mexico

In order for the computer program of the chart plotter to read the screen, and detect signals from a pixal on the screen and know what that signal represented would take a level of technology that has yet to be developed.

Information is displayed on a screen, and the only thing read from a screen is the signal from the position where your mouse is pointing when you click the mouse or press enter.

The chart on the plotter/AIS.Spot, is nothing more than a document scaned and displayed on the screen. Some charts used are reather old as GPS mapping is something quite new. This means that the GPS position is correct - the chart is not.

The whole thing works by some very clever programing by humans who have been known to make mistakes.
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Old 03-05-2012, 23:50   #101
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Re: Sad News Again Off Mexico

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Have they found the skipper yet? Maybe he went over an hour earlier while on solo watch and the boat auto-ed on...and on. Any number of alternatives.
Fascinating theory. And a clear possibility

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BTW, a query to those with chartplotters: surely setting a leg through dry land sets of alarms and strobe light warnings?
They are not quite that smart. At least mine is not. You tell it to plow through the middle of the continent, and it will do its best to obey.
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Old 04-05-2012, 00:41   #102
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Re: Sad News Again Off Mexico

Thanks to the three posters above, Bash, John A and Ex-Calif, for setting me straight on what chartplotters do - and don't (at least yet) do; it's true I had presumed they meshed chart and course data.

I'm keeping my pencils till they get it right...
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Old 04-05-2012, 04:04   #103
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Re: Sad News Again Off Mexico

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Originally Posted by At sea View Post
Thanks to the three posters above, Bash, John A and Ex-Calif, for setting me straight on what chartplotters do - and don't (at least yet) do; it's true I had presumed they meshed chart and course data.

I'm keeping my pencils till they get it right...
All you need to know are the limitations of a CP and then it becomes even more useful. (not essential but very useful nonetheless). More important than using the pencil is knowing how to use it (and what it / you can and can't do with it) - same as for a CP.
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Old 04-05-2012, 04:24   #104
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Re: Sad News Again Off Mexico

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..........So are you saying there is not, or ought not to be, or cannot be, a function on electronic charts that sets off a similar alert in similar circumstances?
As others have said, no it is not done but it could be done easily. The computing power is readily available and the data is available but it wouldn't be cheap and that is probably the main reason it isn't done. The other reason is that there isn't much need for it.

Aircraft do it all the time, it is called EGPWS or TAWS; enhanced ground proximity warning system or terrain awareness warning system. The boxes are small, the terrain databases exist, the GPS is of course available. A marine system would only require a simple two dimensional solution rather than a 3D aviation solution unless one wanted to factor in depth of water and tidal conditions.
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Old 04-05-2012, 04:29   #105
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Re: Sad News Again Off Mexico

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In order for the computer program of the chart plotter to read the screen, and detect signals from a pixal on the screen and know what that signal represented would take a level of technology that has yet to be developed.

Information is displayed on a screen, and the only thing read from a screen is the signal from the position where your mouse is pointing when you click the mouse or press enter.

The chart on the plotter/AIS.Spot, is nothing more than a document scaned and displayed on the screen. Some charts used are reather old as GPS mapping is something quite new. This means that the GPS position is correct - the chart is not.

The whole thing works by some very clever programing by humans who have been known to make mistakes.
Terrain databases already exist and coupled with a GPS position and a GPS derived plan (course), the computing is not that difficult, just requires a need or a will. Neither exist, yet!
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