Nightmare. Do life-rafts sink?

[Robert Wilson]

If unsecured, untethered and washed overboard, would an uninflated valise (and/or cannister) liferaft sink or float?

I woke in a muck sweat last night after dreaming that I'd suffered a knockdown, the valise life-raft had been on the cabin-top, not lashed on and as it hit the water it sank.

I know a raft should be lashed-on with quick-release knots/hydrostatic releases, but it made me think.

 

[awol]

A 6-man Seago canister floats - this I know from personal experience. But surely you would have the painter attached to the boat?

 

[prv]

They float - not much point in a hydrostatic release otherwise, is there?

Pete

 

[Robert Wilson]

A 6-man Seago canister floats - this I know from personal experience. But surely you would have the painter attached to the boat?

By untethered I meant "painter not attached", so it wouldn't have inflated as it went into the water.

As I said, it was a dream, but it made me think about the "floatability" of an un-inflated raft. Very dense, very heavy.

 

[Birdseye]

If unsecured, untethered and washed overboard, would an uninflated valise (and/or cannister) liferaft sink or float?

I woke in a muck sweat last night after dreaming that I'd suffered a knockdown, the valise life-raft had been on the cabin-top, not lashed on and as it hit the water it sank.

I know a raft should be lashed-on with quick-release knots/hydrostatic releases, but it made me think.

quite possible it sinks. Depends on the volume of trapped air and since the air to inflate is in compressed form and of low volume it wont be sufficient on its own. And I cannot imagine a valise holding lots of air and not leaking it out.

 

[DJE]

They float - not much point in a hydrostatic release otherwise, is there?

Pete

Seems like pretty sound reasoning to me.

 

[Sailfree]

Just lifted a 8 valiase man off boat to return to hire company. It was very heavy and difficult to lift so I recon about 35 kg.

Not sure but I would expect it to sink until tether causes it to inflate and then it would quickly come to surface probable long time before fully inflated so it's empty of water.

Still have 4 man canister on board on pushpit but weight of valiase would concern me if a weaker person had to lift it out of a locker in a tired seasick state.

 

[DJE]

Just lifted a 8 valiase man off boat to return to hire company. It was very heavy and difficult to lift so I recon about 35 kg.

Not sure but I would expect it to sink until tether causes it to inflate and then it would quickly come to surface probable long time before fully inflated so it's empty of water.

Still have 4 man canister on board on pushpit but weight of valiase would concern me if a weaker person had to lift it out of a locker in a tired seasick state.

35kg is about 34 litres of seawater or 1.2 cubic feet in old money. Surely an 8-man valise raft would displace more than that and therefore float.

- Heavy stuff this water you know.

 

[FishyInverness]

Sounds like a PBO test case if ever there was one!

 

[Sailfree]

35kg is about 34 litres of seawater or 1.25 cubic feet in old money. Surely a valise would displace more than that and therefore float.

I would estimate that it's weight was nearer 50kg and it occupied 2.5 cu ft. Iirc that displaces some150lb of seawater so you are right it would flat.

Difficult to imagine when you are trying to lift the bloody thing onto a trolley!

 

[prv]

Sounds like a PBO test case if ever there was one!

I think I'd cancel my subscription if they wasted three pages on such a stupid question!

Sorry guys, but it is, and I'm amazed how many people don't seem to know how their kit works.

Pete

 

[Shorn100]

Life rafts float, whether they are in a canister or valise.
Sleep easy.
Shorn

 

[snowleopard]

OK, very simple to work out. Take this random liferaft (6-man canister)

http://www.force4.co.uk/172/Seago-Offshore-Liferaft-6-Man-Canister.html

The dinensions given are 77 x 50 x 29 cm, 38kg.

The displacement of the canister is 77 x 50 x 29 / 1000 kg = 111.65 kg (I've omitted corrections for density of seawater and the shape of the canister not being an exact cuboid as they cancel each other out. It is quite clear that the weight of the raft is 1/3 of the weight of the seawater it displaces so there is no way it is going to sink.

 

[Sailfree]

Prv in our defence I would say that Inflating a life raft in water is not something you normally do. I think most know that you pull the cord to inflate. On sea survival course they use an already inflated life raft but leave it inverted so you have to right it.

 

[fisherman]

To play devil's apricot, what if the raft sank with the boat, say the cradle was inverted: if the raft canister got to a depth where the air spaces in it compressed sufficiently it would not float. The canister is not pressure-proof.

 

[westhinder]

I would estimate that it's weight was nearer 50kg and it occupied 2.5 cu ft. Iirc that displaces some150lb of seawater so you are right it would flat.

Difficult to imagine when you are trying to lift the bloody thing onto a trolley!

Off topic, I know, but as someone raised in a metric universum I have to say it always amazes me how some of you manage to juggle measurements. In this case a mix of imperial and metric.
Surely the purely metric calculation that snowleopard offers is much easier to grasp?
(goes into hiding now;-)

 

[snowleopard]

On sea survival course they use an already inflated life raft but leave it inverted so you have to right it.

They inflated it on my course. It inflated inverted anyway.

 

[snowleopard]

Off topic, I know, but as someone raised in a metric universum I have to say it always amazes me how some of you manage to juggle measurements. In this case a mix of imperial and metric.
Surely the purely metric calculation that snowleopard offers is much easier to grasp?
(goes into hiding now;-)

We had a thread in the Lounge a couple of years back where various old-stagers tried to demonstrate that imperial calculations were just as easy as metric. I don't think they fooled anyone. In my school days everyone worked in imperial outside the lab. Today it is surprising how many people now give dimensions in metric where, 30 years ago you'd have been regarded as a bit of a ponce to talk in metres instead of yards. Let's hope we get rid of the silly hybrid system we have now, particularly in the building trade with timber sold by the 'metric foot' and plasterboard sheets 1200 x 2400 mm but plywood 8' x 4'.

 

[Sailfree]

Off topic, I know, but as someone raised in a metric universum I have to say it always amazes me how some of you manage to juggle measurements. In this case a mix of imperial and metric.
Surely the purely metric calculation that snowleopard offers is much easier to grasp?
(goes into hiding now;-)

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.

Unfortunately many constants stick on your mind eg a cu ft of water weighs 64lb! We are also more adept at conversion eg 5 ltrs is 10%greater than a gallon. 1kg is 10% greater than 2 lb . 1ltrs is 10% less than 2 pints. For many of us it's the best way to get a "feel" for the metric quantity. You are probably the same when converting Kilometers to mls!

 

[bigwow]

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