Nightmare. Do life-rafts sink?

[prv]

I'm only arguing this for fun here Pete, no actual point intended...but....they once pumped a boat full of gas and set off a spark....

Did they really not know what was going to happen at that point? But they did it anyway!

They wanted to demonstrate what a gas explosion looks like, because it's fortunately not something that gets seen very often - and practically never filmed.

How to use a liferaft (the apparent ignorance of which continues to stagger me) is seen on any number of sea-survival courses, and often filmed:

http://youtu.be/JDUvUcCIy5o?t=1m8s

Pete

 

[fireball]

No, what is the point in a hydrostatic release in a life raft that sinks? It won't be released even if the hydrostatic release works because it will sink with the boat. The whole point is that the hydrostatic release releases the raft which then floats up and deploys/is deployed.

unless you expect someone to swim down to the raft siting in its sinking cradle and pull all the painter out and deploy it underwater.

See - that's why you need to think these things through - perfectly logical once you think about all the aspects - but dangerous if someone has assumed something - like perhaps the hydrostatic device triggers the inflation of the liferaft? Not entirely unreasonable assumption I wouldn't think ... (not that we had one)

 

[prv]

As we're on about 4 pages of forum thread perhaps it is worth a 3 page spread in PBO ....

You're starting to convince me now. Apparently there are lots of people who do not understand how to launch a liferaft, or what a hydrostatic release is and how it's supposed to work. I never would have guessed it - I thought this was basic knowledge that (almost) everyone who goes to sea understood. Three pages might still be a bit patronising, but a single-page "skipper's tips" type card might have value.

Out of interest, do those who didn't know they were supposed to throw the raft overboard (or thought it would sink if they did), or those who didn't know that it's supposed to float up and pull its own painter after being released by the hydro unit - do these people have rafts (and hydro units) on their own boats?

Pete

 

[bedouin]

All liferafts must float in their uninflated state. What is more there must be enough buoyancy to trigger the automatic inflation mechanism.

Once the liferaft is inflated then there must be enough buoyancy to break the painter if it is still tethered to a sinking boat.

 

[prv]

Once the liferaft is inflated then there must be enough buoyancy to break the painter if it is still tethered to a sinking boat.

Not sure that part is strictly true - it's the plastic weak link attached to the hydro unit which breaks, rather than the painter. Hammar at least have different coloured links for different sized rafts, because the link intended for a 25-man commercial raft might not break even with an inflated 4-man tugging on it.

A few years ago the MCA (or possibly SeaFish or similar) put out a warning that during surveys they had found several cases of painters being secured to the wrong place. Some were secured through the HRU loop only, so if the HRU had fired the raft would float to the surface without pulling the painter and inflating. Others were secured to strong points so that they would not break free, and the MCA seemed to be of the opinion that they might be dragged down with the ship rather than breaking free. They could be wrong in that (it seems like a hell of a lot of force to expect the painter attachment to take) but either way it's not the designed method of release.

If you have an HRU, the painter needs to be attached through both the HRU loop (so that it is strongly attached if you release the senhouse slip and throw the raft over manually) and through the red plastic link so that, once the loop is cut, it is secured weakly enough to break free. Maybe worth a check if you have a hydro unit?

Pete

 

[bedouin]

Not sure that part is strictly true - it's the plastic weak link attached to the hydro unit which breaks, rather than the painter. Hammar at least have different coloured links for different sized rafts, because the link intended for a 25-man commercial raft might not break even with an inflated 4-man tugging on it.

A few years ago the MCA (or possibly SeaFish or similar) put out a warning that during surveys they had found several cases of painters being secured to the wrong place. Some were secured through the HRU loop, so if the HRU had fired the raft would float to the surface without pulling the painter and inflating. Others were secured to strong points so that they would not break free, and the MCA seemed to be of the opinion that they might be dragged down with the ship rather than breaking free. They could be wrong in that (it seems like a hell of a lot of force to expect the painter attachment to take) but either way it's not the designed method of release.

Pete

You are confusing two different issues.

The hydrostatic unit is there to release the liferaft from a cradle (if it has one) should the boat sink. Not all liferafts are deployed in cradles. But for any liferaft a requirement of the standard(s) is that if it is secured to a sinking boat it should inflate and not be dragged down - hence those requirements.

So there are specific requirements on the breaking strain of the painter on the Liferaft (often achieved by giving it a deliberate weak link). It must not break under the strain required to inflate the liferaft, but must break rather than let the liferaft be pulled under.

 

[westhinder]

I think it's down to having units of the right size for the question you're thinking about. This started with a consideration of a volume of 1 or 2 cubic feet. That is much easier to grasp than .03 to .06 cubic metres. 30 to 60 litres is easier but somehow relates more to liquids than solids. I'm baffled by the way the UK construction industry has taken to millimetres and metres for lengths whereas the continentals use centimetres which seem to have a much more human scale. (eg 12metres 37 vs 12370mm).

I absolutely agree with you. That is how we grow into the scales, metres and centimetres are what you can relate to. Millimetres come later, decimeters are hardly ever used, except on charts, come to think of it. I suspect millimetres are important in engineering and will have made their way into some fields. And apparently as it was all strange anyway, no one will have realised that centimetres are the more common measure.

 

[pmagowan]

I absolutely agree with you. That is how we grow into the scales, metres and centimetres are what you can relate to. Millimetres come later, decimeters are hardly ever used, except on charts, come to think of it. I suspect millimetres are important in engineering and will have made their way into some fields. And apparently as it was all strange anyway, no one will have realised that centimetres are the more common measure.

Yes, mm got in through architectural and engineering drawings and the builders didn't know how to move a decimal place.

 

[fireball]

You're starting to convince me now. Apparently there are lots of people who do not understand how to launch a liferaft, or what a hydrostatic release is and how it's supposed to work. I never would have guessed it - I thought this was basic knowledge that (almost) everyone who goes to sea understood. Three pages might still be a bit patronising, but a single-page "skipper's tips" type card might have value.

Out of interest, do those who didn't know they were supposed to throw the raft overboard (or thought it would sink if they did), or those who didn't know that it's supposed to float up and pull its own painter after being released by the hydro unit - do these people have rafts (and hydro units) on their own boats?

Pete

Only owned a liferaft briefly - as it was a valise it was kept in a locker - my understanding was that basically we lobbed it over the side and pulled the painter - it inflated. Never occurred to me to think about if it would float or sink prior to inflation. I'm assuming it didn't have a hydrostatic inflation mechanism as it wasn't going to be surface mounted - but I could be wrong there too - I suppose we could've tied off the painter and left it somewhere it could float free if the boat sunk, but it really wasn't a concern we thought worth worrying about.

There's lots of kit that many of us don't know all the particulars about - just enough to get by ...

 

[onesea]

It's a sign of age. I started my engineering qualifications in imperial. Eg working out brick quoins in various wall thicknesses and bonds. A brick was 9" and walls a combination of 4.5" plus any cavities. A sheet of ply was 8' x 4'. Then we went metric but at first nothing changed as manufacturing plant was not replaced. The imperial dimensions were just rounded into metric eg brick 225mm and ply 2.4m x 1.2m ! A lot of stuff is still imperial based but quoted in a metric number. Most building wall lengths will still be a multiple of 9"!

I finished my HNC and BSc in metric. Metric is easier to use but imperial grew out of convenient numbers so it has more meaning for people. When responsible for graduate engineers they had no concept of what 100kN was but talk about 8 ton lorries and they could visualise it.

I use both badly, I "see" a boats length in feet but its sail area in meters. I worked in an industry where it was not uncommon to make bags 6" diameter buy 2m long, or even better when they extended a unit 6" dia x 6' 1m long (around about 2.83m). It got confusing when they brought in new plant is that the 6" dia one or the 150m dia one?

Dont even start me on Cement, how many sacks are in a jumbo sack? particulary if dealing with americans you can have hours of fun

When my pontoon neighbour was removing his liferaft from the pushpit cradle he dropped it. It floated!:encouragement:

I accept the calculations given prove that a liferaft will float, but it does assume that water will not leak into the canister. Mine has no seal and would over a period of time in a seaway flood and ultimately sink, much like me!

This "should" be designed out of it.

Link to my earlier explination on HRU's
http://www.ybw.com/forums/showthread.php?305891-Is-a-hydrostatic-release-for-the-liferaft-a-good-thing&p=3404048#post3404048

I say should because some life saving ideas do not strike me as practical....

 

[FishyInverness]

Here's a nice pretty vid to show you how the HRU works

https://www.youtube.com/watch?v=0nin0jpPig8

 

[Salty John]

They float:

https://www.youtube.com/watch?v=sm9VwvpmWZE

Remember not to give up pulling the tether until the raft inflates - there's a lot more line than you might think.

 

[TQA]

Well if anyone wants to have nightmares about liferafts they should read the account of the 1979 Fastnet Race " Fastnet Force Ten "then follow that up with the 2014 story of how the three guys on Taos who deployed their liferaft, it inflated caught the wind [ it was blowing a hooley] the painter pulled off the raft and the raft blew away.

 

[pmagowan]

Which anchor do you take with you when you retreat to the liferaft and does the choice depend on whether you are departing a sinking submarine or AWB?

I'll get my coat...

 

[DJE]

Which anchor do you take with you when you retreat to the liferaft and does the choice depend on whether you are departing a sinking submarine or AWB?

I'll get my coat...

This thread reminds me that the sailing club AGM is approaching. :ambivalence:

 

[Daedelus]

The float. I was putting my Viking Rescyou 4 back in it's cradle when I dropped it (it's flippin heavy -around 40kg) and it floated gently down the line of trots in the marina. The marina staff had to come out in their dory and get it back for me. I now let them put it back anyway, seems easier and they haven't dropped it yet.

 

[FishyInverness]

Which anchor do you take with you when you retreat to the liferaft and does the choice depend on whether you are departing a sinking submarine or AWB?

I'll get my coat...

Who cares about this? The real issue is what Ensign do you wear in the Liferaft, and do you lower it if it takes longer than 12 hours to be rescued?!

 

[pmagowan]

Who cares about this? The real issue is what Ensign do you wear in the Liferaft, and do you lower it if it takes longer than 12 hours to be rescued?!

Well, it depends on where your liferaft sinks. If it is in international waters and there are no other craft around one might get away without the ensign, especially at night. It would be necessary to get it up tout sweet if you drift into a foreign port. The real question is where do you fly your ensign and is there a recognised place to fly it from in the event your liferaft sinks. In war films the Americans generally let their 'flag' drift to the bottom in an atmospheric way with the sunlight twinking behind it. Certainly if you are riding your sinking liferaft to the bottom this is most aesthetically pleasing but it is unlikely that the Americans have the correct ettiquette so we should probably dismiss it out of hand.

Now what do you do if your RYS member or RYC member succumbs to the deep first, do you swap the white for a blue and then the blue for a red?

 

[FishyInverness]

 

[Robert Wilson]

Well, thank you folks. That certainly stirred-up more than I thought!
I for one work/measure materials in metric, walk in imperial, fill-up the car in metric but work-out consumption in imperial MPG, drink in metric and imperial, weigh myself in imperial, cook in metric but pour imperial milk onto my metric-packaged cornflakes.

As for float/not float liferafts:-
Firstly I am relieved but not surprised they float - otherwise they'd sink a long way before the tethered painter inflated the raft which would then breach like a whale after eating too much cabbage.

Secondly, I had realised that the raft has to be conveniently located and suitably secured, for immediate release.

Thirdly, I have never seen one deployed, and hope I never have to be needing one. But I have one, just in case.

Fourthly, I would expect that a fluttering ensign would get in the way of the winchman, so I shall not be making arrangements to take one with me. Unless of course I have been enrolled in the RYS :encouragement: