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Old 26-06-2014, 19:45   #16
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Re: Lifeboat Navigation

A sextant with an instruction book could while away the hours once the batteries on the electric brunette ran out.
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Old 26-06-2014, 20:23   #17
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Re: Lifeboat Navigation

Quote:
Originally Posted by Jammer Six View Post
Here's what I don't understand: the logic behind lifeboat equipment choice advice.

Davis, for example, recommends their cheapest, least accurate sextant, a plastic triangle, for a lifeboat sextant...
That's the very sextant onboard TN to backup the navigation electronics.
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Old 26-06-2014, 20:42   #18
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Re: Lifeboat Navigation

The only bit of kit you need packed in a liferaft these days is an EPIRB.
You really don't want to watch your yacht sink and then go through the 'but I thought you brought the epirb?' 'No that was your job...''No......
That scenario cost three Tasmanians their lives about 10 years ago.....
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Old 26-06-2014, 20:58   #19
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Re: Lifeboat Navigation

Bligh's trip from the site of the mutiny to Timor was an amazing feat of navigation and seamanship. He used the tools of the day - those that were given to him. His knowledge of the area, gleaned from his previous travels to the area, were what he used instead of the charts that Christian denied him.

Bligh would have been glad to use modern equipment, of course. He didn't use the sextant out of a misplaced sense of sentimentality - it was the best technology of the day. Like the GPS is now. Make sure you have spare batteries in your abandon ship bag, a spare GPS, a good EPIRB and a radio/sat phone as well.

I can't even imagine trying to use a sextant in an inflatable raft. Woah, Nellie.
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Old 26-06-2014, 21:16   #20
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Re: Lifeboat Navigation

Nothing about navigation in this thread means squat, if you dont have WATER. Try doing a sun shot after 2 days without WATER. Try breathing after 3 days without WATER. I would want an epirb, but $100 worth of bottled water would most likely keep you alive longer. On a typical(if there is such a thing) Mom and Pop cruising boat a 4 person life raft serves fine, but a 6 person raft with a much larger supply of water might be more practical. Dehydration ruins the decision making process. _____Just my 2 cents worth. ______Grant.
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Old 26-06-2014, 22:54   #21
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Re: Lifeboat Navigation

The OP's scenario was for a lifeboat not a liferaft, thus at least some minor control of your course was implied.

The Mark 3 is not Davis's least accurate sextant. I read a reasoned argument at Strait of Magellan: Celestial Navigation 101 indicating that the Mark 3 is more accurate than the 15 or 25 even new out of the box.

Why go for the cheaper resource for the ditch kit? Several reasons I can see.
A) You don't need great accuracy in a lifeboat except in a very few locations such as the south pacific where the only islands you can hit for thousands of miles are very small. Most places you will have a fairly large target to hit so 15nm either way would be acceptable. Greater accuracy would require greater size and weight in the ditch kit.
B) Minimizing the cost of this item and its ancillary equipment allows you to spend more money on other safety gear to stow in the lifeboat or ditch bag. All told you would need $150 or so for the whole setup including sextant, long term almanac with reduction tables, 3 watches and a good case. That's about the cost of a cheap GPS.
C) The Mark 3 being dirt simple also means there is a lot less to go wrong.
D) The vernier reading helps keep you from developing a false sense of precision about your results. A pity more people can't keep this idea in mind when using the results of their GPS.

As implied in the first sentence all this is dependent on having a lifeboat with some control. In a liferaft I wouldn't bother with a sextant or a GPS, what's the point?
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Old 27-06-2014, 00:40   #22
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Re: Lifeboat Navigation

Quote:
Originally Posted by crazyoldboatguy View Post

Bligh would have been glad to use modern equipment, of course. He didn't use the sextant out of a misplaced sense of sentimentality - it was the best technology of the day. Like the GPS is now. Make sure you have spare batteries in your abandon ship bag, a spare GPS, a good EPIRB and a radio/sat phone as well.

I can't even imagine trying to use a sextant in an inflatable raft. Woah, Nellie.
Yeah - And to call Bligh's lifeboat a liferaft would be a misnomer...

Quote:
Originally Posted by gjordan View Post
Nothing about navigation in this thread means squat, if you dont have WATER. Try doing a sun shot after 2 days without WATER. Try breathing after 3 days without WATER. .
Doesn't matter how much water you bring unless you know how long you will be out there.

I'd pack at least 2 of these.

PUR Survivor 06 LS Manual Watermaker

What was the couple that was adrift for 67 days? They caught birds and turtles and fish by hand. They patched holes in their raft.

But they made water - Without this they are dead.

Quote:
Originally Posted by Adelie View Post
The OP's scenario was for a lifeboat not a liferaft, thus at least some minor control of your course was implied.
I think Jammer can weigh in but not many around here will have a lifeboat big enough and stable enough to take sightings.

Many other things I would take before a sextant and reduction tables.

But the thread is titled "lifeboat navigation" so for me - Best handheld gps I would look at one of these before spare batteries.

Gogen Emergency Survival Generator Hand Crank Solar Charger Ppt Pr..

So the start of my list is

- EPIRB
- Water maker
- Food
- Sat Phone
- Generator
- iphone in Rhino case
- GPS
- DC chargers
- Raft repair and tools including pump etc
- PPE - Sunblock, hats, long sleeve shirts, medical supplies, prescription meds if I use them
- Signalling -Flares, mirror, air horn, water dye

I am sure there is more but this is a good start.

The phone may raise eyebrows but it has a ton of uses. First is back up gps. I could store survival manuals and data (be nice to know where the shipping lanes are), books to read, games to play so I don't go batshit crazy. If one got imaginative they could find other ways to use a "computer" on board a raft.

In regards to mirror - People have to be looking at least in the quadrant a flare is fired to see it at day. With a fortunate sun angle you'd stand better to shine a spot at the bridge of a ship.
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Old 27-06-2014, 04:24   #23
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Re: Lifeboat Navigation

Today under GMDSS the average time in a liferaft is less then 1day. The maximum expected time is 4 days. This assumes am epirb alert.

Hence long term liferart stays are not a feature of modern rescues. Hence your equipment needs to be tailored to this

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Old 27-06-2014, 09:14   #24
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Re: Lifeboat Navigation

Quote:
Originally Posted by goboatingnow View Post
Bligh from records in his personal journal had a personal sextant and a quadrant

"According to Bligh's notebook, he was equipped with a magnetic compass needle, a 10 inch sextant, a quadrant and two books containing mathematical, astronomical and geographic information on the enforced journey aboard the launch. Within days they knotted a log-line and the men learned to count seconds accurately so as to estimate their speed. Bligh already had a knowledge of the waters gained from his voyage with Cook and, on a personal level, the ability to focus on the minutiae to the exclusion of all else. This last trait may have triggered the mutiny but it was this very quality that was now to save his life and those of the men with him."

Source UK national maritime museum

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That is interesting that he had a quadrant. It is somewhat analogous to someone today having a hand held GPS unit and a sextant, as today a sextant is 200+ year old technology and the quadrant in Bligh's time was almost 200 years old; in Bligh's time the sextant was cutting edge technology much as the GPS is for us today.
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Old 27-06-2014, 10:38   #25
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Lifeboat Navigation

Quote:
Originally Posted by Ex-Calif View Post
I think Jammer can weigh in but not many around here will have a lifeboat big enough and stable enough to take sightings.

The advantage of a sextant or octant over the earlier quadrant was that the image of the body being that was stabilized relative to the horizon and the instrument retained some accuracy even in rough weather.

In storm seas you won't be able to take sights but neither will you be able actively steer the lifeboat. About the time you can start to control the direction of a lifeboat you should be able to take sights.

Unless your "lifeboat" is an inner tube, at some point it will be stable enough to shoot.



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Old 27-06-2014, 11:25   #26
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Re: Lifeboat Navigation

In a modern fully enclosed lifeboat you wont be going much further than you would in your liferaft... the days of setting your dipping lugsail, breaking out your lifeboat charts ( no longer included in lifeboat kit) and heading for Africa are long gone.
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Old 27-06-2014, 11:32   #27
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Re: Lifeboat Navigation

In addition, I would think it would be to one's advantage to stay as much in one place as possible. Actively moving doesn't help SAR efforts.

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Old 27-06-2014, 12:27   #28
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Re: Lifeboat Navigation

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Originally Posted by colemj View Post
Frankly, I'm surprised anyone recommended a sextant of any type. Not only is it fairly useless without reduction tables, chrono, charts, etc like others said, there are very few people anymore who even know how to use one (I'm one of those).

I would consider a sextant as a duct-tape approach to equipment choice for a liferaft. I agree that you want good and proper equipment in an emergency - that would be your epirb, your DSC radio and your backup epirb.

I'm curious - how do you think a sextant will help you if you abandoned ship to a liferaft?

Mark
Not true. A nautical almanac is all that's needed for a noon sight and that's not even necessary if you just want a rough latitude. The NA also contains a tables for sight reduction.
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Old 27-06-2014, 13:57   #29
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Re: Lifeboat Navigation

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Not true. A nautical almanac is all that's needed for a noon sight and that's not even necessary if you just want a rough latitude. The NA also contains a tables for sight reduction.
OK, so how about my statement that few people even know how to use one?

And no one has answered the question about just what one would DO with a sextant in a liferaft. One is not navigating in a liferaft.

Seems like something that could be broken and poke a hole in the raft to me. Certainly the $60 would be better off spent on other useful items.

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Old 27-06-2014, 15:04   #30
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Re: Lifeboat Navigation

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Originally Posted by colemj View Post
OK, so how about my statement that few people even know how to use one?

And no one has answered the question about just what one would DO with a sextant in a liferaft. One is not navigating in a liferaft.

Seems like something that could be broken and poke a hole in the raft to me. Certainly the $60 would be better off spent on other useful items.

Mark
Well, I know. But I agree that few others do. I don't claim that it's a necessity, but neither do I think it's a 'waste of time.'
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