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Old 21-10-2012, 16:29   #31
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Re: How to sever the liferaft painter?

It's a bit of a Hobson's choice:
  • would you prefer your raft to be pulled under - or, perhaps more likely, having the patch ripped out, leaving it crippled - in a sudden sinking before you can get to it, and find and use the knife, or
  • would you prefer it to exit the scene in tumbleweed mode when launched in a storm?
Seems to me there are a couple of avenues to follow to try and have it both ways. (or perhaps I should say, NOT have it either way)


In an ideal world, the "self tending" gold standard might be a strong weak link: strong enough that it would only break when the attachment of the D-ring was about to rip out of the raft.

This is not as easy as it sounds, though. The concept is feasible when trying to protect rigid structures made from engineering materials whose properties don't change. I'm thinking of shearpins and the like.

Unfortunately it seems to me the material of most rafts probably doesn't support this ideal, but for a Hypalon raft it might be a possibility.

As I understand it, the usual liferaft material has quite serious potential for progressive deterioration over time and with storage. It's not realistic to engineer a "strong weak link" when the target keeps shifting.

The way this subject is sometimes discussed (often in the context of explaining away failures of rafts which were a little past their service date), you'd think the material properties followed a straight level line until that date, at which point they suddenly and mysteriously lost their integrity.

My experience of deterioration in such materials is that it tends to be a lot less predictable and orderly , much as engineers would wish it to be otherwise.


The second idea, and one I would favour, would be to put a (strongish) weak link at the yacht end of the tether, and to leave that as the default option. If the yacht sank quickly, this would protect the raft from being submerged or damaged. In a storm-force launching, when the yacht was not in a rapid sinking condition, a clip on the painter, outboard of the link, could be clipped to the yacht to 'defeat' the weak link.

ON EDIT:
I realised after posting that my reasoning is underlaid and possibly undermined by my unverified assumption that the patch would be at risk of pulling out before the raft would submerge.

If this is not the case, the "strong weak link" would have to be weaker than I imagine, because its primary function would be to prevent the raft being pulled under. The good thing is that the maximum buoyancy of the raft is a known quantity, so this link could be relatively easily engineered.

And (in the strong-wind scenario) the weaker link could be just as easily defeated as a stronger one.
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Old 21-10-2012, 17:02   #32
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Re: How to sever the liferaft painter?

This is what happens if you are unable to launch your life raft manually when fitted with the H20, click on the movie logo in the link>>>...hammar-mod.....no need for a knife...

An example (on the right) of a supplied life raft safety knife if you do need to cut the painter...(we have this type of knife fitted to all our life rafts)...



A lot of good info here...H20 Small Rafts model - CM Hammar
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Old 21-10-2012, 17:04   #33
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Re: How to sever the liferaft painter?

ON FURTHER EDIT (would have applied to previous post, but period had expired.)

A hydrostatic release at the yacht end would be sufficient to protect against submersion. No weak link needed.

Mi estupidez
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Old 21-10-2012, 17:14   #34
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Re: How to sever the liferaft painter?

Quote:
Originally Posted by Andrew Troup View Post
ON FURTHER EDIT (would have applied to previous post, but period had expired.)

A hydrostatic release at the yacht end would be sufficient to protect against submersion. No weak link needed.

Mi estupidez
That is where the hydrostatic release should be, they need to have the weak link to self realease from the vessel if no one is able to....see the movie in the link i posted above....
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Old 21-10-2012, 17:47   #35
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Re: How to sever the liferaft painter?

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Originally Posted by IslandHopper View Post
That is where the hydrostatic release should be, they need to have the weak link to self realease from the vessel if no one is able to....see the movie in the link i posted above....
Hmmm ... not sure I follow. Seems to me if there's a hydrostatic release at the yacht, and a knife at the raft, you don't actually need a weak link ?

What have I missed ?

ON EDIT

OK, terminology thing: I'm thinking of a hydrostatic release of the painter, as a substitute for a weak link. Obviously there also can previously (in fact must) be a hydrostatic release of the canister, so maybe we're talking at cross purposes.
The hypothetical hydrostatic release of the painter would happen at something approaching the depth difference from the canister release depth represented by the length of the painter.
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Old 21-10-2012, 17:54   #36
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Re: How to sever the liferaft painter?

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Originally Posted by Andrew Troup View Post
Hmmm ... not sure I follow. Seems to me if there's a hydrostatic release at the yacht, and a knife at the raft, you don't actually need a weak link ?

What have I missed ?
What if nobody is in the raft at the time of the vessel sinking....?
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Old 21-10-2012, 18:03   #37
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Re: How to sever the liferaft painter?

I should probably apologise and withdraw.

I don't have anything useful to contribute in this thread because I don't know enough about the topic. I haven't previously been a great fan of liferafts, preferring some variation of the survival boat concept

I strayed in here in the hope of educating myself, in hopeful expectation that the things which make me queasy about liferafts will be addressed, and I want to keep abreast on what progress is being made in that direction.

I'll shut up and sit on my hands.

ON EDIT
Ooops, just spotted IslandHopper's question

if nobody is in the raft at the time of the vessel sinking -

wouldn't a hydrostatic painter release (on the yacht) still serve the same purpose as a weak link?
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Old 22-10-2012, 06:42   #38
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Re: How to sever the liferaft painter?

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Originally Posted by estarzinger View Post
However, I do know that people who have vast specific knowledge and data and expertise write these ISO and ISAF recommendations.
I suspect you're joking here.


[QUOTE=Andrew Troup;1064441]I should probably apologise and withdraw.

I don't have anything useful to contribute in this thread because I don't know enough about the topic. QUOTE]

I know you're joking!
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Old 22-10-2012, 06:52   #39
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Re: How to sever the liferaft painter?

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Originally Posted by Blue Crab View Post
I suspect you're joking here.
. . .
I know you're joking!


I believe Andrew T and I share some general misgivings about life rafts.
Mine are reasonably well known.
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Old 22-10-2012, 07:09   #40
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Re: How to sever the liferaft painter?

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Originally Posted by estarzinger View Post
The official position is that empirical experience says is that there is a much greater risk of the raft accidentally breaking away with a weak link than of a raft being dragged under without a weak link.
I' guessing that by "accidently breaking away", they are referring to the fact that the raft has been manually launched and is intentionally left tethered to the yacht. In that case, if the raft has been launched, then the crew will be immediately boarding, as to launch the raft idicates they have made the decision to abandon. If it was me, then I would have shifted the painter to a strong point, then cut once in the raft.

My preference would be to have the weak link in place, if the boat was run down and sank, I would like to see the raft pop up at some stage, hopefully intact, and not a big hole where the painter had been fixed to the raft.
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Old 22-10-2012, 12:09   #41
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Re: How to sever the liferaft painter?

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if the raft has been launched, then the crew will be immediately boarding, as to launch the raft idicates they have made the decision to abandon.
The universally agreed rule is something like "don't board the raft until you have to step up into it". Although this rule does not necessarily work in the most common case today, when the raft is used as a transfer vessel (to a rescue ship) or helo pick point, perhaps for an injured crew member, rather than in the traditional 'life raft for days' mode.

It's not universally agreed when to launch the raft. You propose one rule "not until you have made a decision to abandon", but others would suggest launching earlier "just in case and to be prepared" - lets say the interior is on fire and you have half the crew fighting the fire . . . I could imagine telling the other crew to launch and ready the raft while we still don't know if we will get the fire out or not and thus have not made a final decision on abandoning or not. I think this (when to launch the raft) is a case of 'it depends on the situation'.

But even with your suggested rule . . . the fact the have decided to abandon does not mean they are immediately ready to board the raft. They might want to wait for a rescue helo/ship to come into sight for instance. And in that time period a weak link might break and the raft be lost.
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Old 22-10-2012, 12:39   #42
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Re: How to sever the liferaft painter?

Quote:
Originally Posted by estarzinger View Post
The universally agreed rule is something like "don't board the raft until you have to step up into it". Although this rule does not necessarily work in the most common case today, when the raft is used as a transfer vessel (to a rescue ship) or helo pick point, perhaps for an injured crew member, rather than in the traditional 'life raft for days' mode.

It's not universally agreed when to launch the raft. You propose one rule "not until you have made a decision to abandon", but others would suggest launching earlier "just in case and to be prepared" - lets say the interior is on fire and you have half the crew fighting the fire . . . I could imagine telling the other crew to launch and ready the raft while we still don't know if we will get the fire out or not and thus have not made a final decision on abandoning or not. I think this (when to launch the raft) is a case of 'it depends on the situation'.

But even with your suggested rule . . . the fact the have decided to abandon does not mean they are immediately ready to board the raft. They might want to wait for a rescue helo/ship to come into sight for instance. And in that time period a weak link might break and the raft be lost.
Hence why the recommended procedure when manually launching the raft is to always transfer the painter to a strong point, the weak link is there purely to free the raft from the vessel without human intervention in a sudden sinking situation......
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Old 22-10-2012, 12:45   #43
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Re: How to sever the liferaft painter?

No, you should already have a knife or two...I like the ones with a rounded point and a serrated cutting edge. Touch a taut line and it parts...
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Old 22-10-2012, 14:14   #44
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Re: How to sever the liferaft painter?

Quote:
Originally Posted by nigel1 View Post
I' guessing that by "accidently breaking away", they are referring to the fact that the raft has been manually launched and is intentionally left tethered to the yacht. In that case, if the raft has been launched, then the crew will be immediately boarding, as to launch the raft idicates they have made the decision to abandon. If it was me, then I would have shifted the painter to a strong point, then cut once in the raft.

My preference would be to have the weak link in place, if the boat was run down and sank, I would like to see the raft pop up at some stage, hopefully intact, and not a big hole where the painter had been fixed to the raft.
I'm not experienced on this but my logic tells me to be concerned about the circumstances most likely to incur forced usage of an inflatable liferaft. For me it is likely to be in extreme waves/winds and I fear the inflatable being blown over the water away from me and me not being able to swim to it in such rough conditions?
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Old 22-10-2012, 14:18   #45
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Re: How to sever the liferaft painter?

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Originally Posted by IslandHopper View Post
Hence why the recommended procedure when manually launching the raft is to always transfer the painter to a strong point, the weak link is there purely to free the raft from the vessel without human intervention in a sudden sinking situation......

Thanks for pointing that out John, I was going to quiote from our liferaft Šlaunching instructions, but when I looked, the bit about attaching to the strong point was not there. Norwegian poster with translation, so may be lost somewhere, but thats what I recall the instructions stating, if lauched by hand, secure painter to a strong point.

BTW how was the tow
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