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Old 26-06-2014, 10:34   #1
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Lifeboat Navigation

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.

I learned in diving that an emergency is when you want your best equipment, not your cheapest. You want the most foolproof, reliable and easy to use equipment, not the one made out of cardboard.

So I don't understand the duct tape approach to emergency, life and death equipment choices.
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Old 26-06-2014, 11:04   #2
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Re: Lifeboat Navigation

Well, for one you will not be able to sail anywhere in the liferaft. You're at the mercy of the sea. An accurate position will not do much. A sextant (plastic or otherwise) will not help much in an emergency situation. If you need a position your i-phone would work better (make sure it's in a ziplock).

I would think a sextant in a liferaft or lifeboat would be an anachronism. Captain Bligh had one (actually a quadrant I think) on his sail to Timor but liferafts and lifeboats today don't sail.
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Old 26-06-2014, 16:14   #3
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Lifeboat Navigation

As said navigating a life raft is note of much importance. A sextant, with reduction tables, charts, chronograph etc. is probably the worst solution available. Coupled that with everything being soaking wet, crew scared s**tless, seasickness, possible injuries, over cast skies if storm was responsible for being in the life raft, no one is going to be hopping up for a noon site. Waterproof handheld gps, and of course your epirb are the best solution to being found. GPS coords can help if you are able to communicate with anyone, and you can even buy handheld vhf with built in gps.


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Old 26-06-2014, 16:35   #4
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Re: Lifeboat Navigation

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?

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Old 26-06-2014, 16:52   #5
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Re: Lifeboat Navigation

Getting back to the OP's question re quality of sextant to be used in a life raft: disregarding the problems of actually using the sextant observations in that environment, the limits of accuracy are set not by the quality of the instrument but the physical difficulty of making the observation from an unstable, bobbing raft, with a canopy overhead and a height of eye of only a few feet. The basic Davis sextant, besides being fairly durable is certainly accurate enough that it will not be the limiting factor. What this means is that your results would be no more reliable with the very best instrument available.

Cheers,

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Old 26-06-2014, 16:58   #6
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Re: Lifeboat Navigation

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Originally Posted by Jim Cate View Post
Getting back to the OP's question re quality of sextant to be used in a life raft: disregarding the problems of actually using the sextant observations in that environment, the limits of accuracy are set not by the quality of the instrument but the physical difficulty of making the observation from an unstable, bobbing raft, with a canopy overhead and a height of eye of only a few feet. The basic Davis sextant, besides being fairly durable is certainly accurate enough that it will not be the limiting factor. What this means is that your results would be no more reliable with the very best instrument available.

Cheers,

Jim

Why do you need to know where you are, in a liferaft. Surely the key is that others know where you are ????

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Old 26-06-2014, 17:04   #7
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Re: Lifeboat Navigation

Quote:
Captain Bligh had one (actually a quadrant I think) on his sail to Timor but liferafts and lifeboats today don't sail.
Bligh I believe had a sextant, which had been invented some 32 years before and was the latest navigational instrument of the day, having pretty much superseded the earlier octant of 1730 in the Royal Navy (although the less expensive octant continued to be used in smaller merchant and fishing ships). The octant and sextant had entirely replaced the Davis Quadrant of 1594.
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Old 26-06-2014, 17:27   #8
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Re: Lifeboat Navigation

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Originally Posted by Astrid View Post
Bligh I believe had a sextant, which had been invented some 32 years before and was the latest navigational instrument of the day, having pretty much superseded the earlier octant of 1730 in the Royal Navy (although the less expensive octant continued to be used in smaller merchant and fishing ships). The octant and sextant had entirely replaced the Davis Quadrant of 1594.

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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Old 26-06-2014, 17:48   #9
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Re: Lifeboat Navigation

Try to let go of the sextant, guys. I shouldn't have mentioned sextants, all it did was distract you guys. It was like waving the shiniest word in a sentence in front of magpies. My mistake.

This is about the attitude of using the cheapest equipment available in lifeboats.
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Old 26-06-2014, 17:54   #10
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Re: Lifeboat Navigation

In that case, I think Jim answered it quite well, although he was specifically talking about the sextant. I think his answer can also be more generalized to what can reasonably be used in that situation.

What other pieces of equipment concern you? I would want a very good epirb, radio and backup epirb. After that, some basic supplies, a very good flashlight, very good flares and something to keep me warm when everything is wet.

Maybe an electric wench for that last one?

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Old 26-06-2014, 17:56   #11
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Re: Lifeboat Navigation

Does the electric wench come in brunette?
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Old 26-06-2014, 17:56   #12
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Re: Lifeboat Navigation

I suppose plotting where i was going could keep me from going nuts. And a sextant is a lot less complex than a gps/etc with literally millions of ways to fail.

Not that I think its a particularly practical piece of gear for a liferaft, just playing devils advocate. I personally dont even know how to use one.

As far as why its all the cheapest stuff, who wants to keep all their best toys hidden in a liferaft they'll never use?
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Old 26-06-2014, 17:59   #13
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Re: Lifeboat Navigation

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Originally Posted by Jammer Six View Post
Does the electric wench come in brunette?
See - there you go - already asking for the cheapest one…

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Old 26-06-2014, 18:09   #14
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Re: Lifeboat Navigation

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Originally Posted by colemj View Post
See - there you go - already asking for the cheapest one…
Only for the lifeboat. Onboard, I want a pair of the most expensive models available.
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Old 26-06-2014, 19:08   #15
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Re: Lifeboat Navigation

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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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