Nightmare. Do life-rafts sink?

[pmagowan]

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;-)

I had exactly the same bamboozlement.

I can use both in some situations but not at the same time.

 

[Wandering Star]

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'.

i have to own up to having severe metric dyslexia. We're looking at houses in Ireland and the details usually give the areas in sq metres, I have the greatest difficulty forming an image of the room sizes in my head and need to convert the metric to imperial to make sense of them.

 

[FWB]

Metric or Imperial?

I think it's nice to have both.
I can't imagine boat lengths in metres nor how much water is under my keel... my sounder,tide tables, charts are all in feet.
I can though see how it's easier to calculate if a liferaft valise will float if the calculations are done in metric.

 

[Adonnante]

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!

Peter.

 

[bigwow]

I can only think in imperial, however when I built Bigwow the plans were all metric. This really concentrated the mind when marking out, cutting etc so I feel less mistakes were made than would have been the case if the plans had been in imperial.

 

[pmagowan]

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!

Peter.

Well, sea water is bouyancy neutral in sea water (obviously) so it really then depends on the density of the various parts of the liferaft. It seems likely that most of it is less dense than sea water. I suspect it would float even if all the air in the container was replaced with sea water.

re measurements, my boat is all imperial but anything scientific really needs to be metric for ease of calculation, IMO.

 

[DJE]

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;-)

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).

 

[fireball]

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

It's not a stupid question - nobody knows how their kit works until they ask the question.

 

[prv]

It's not a stupid question - nobody knows how their kit works until they ask the question.

It's not stupid for someone to ask here if they really don't know. It's not stupid for PBO to mention it in an article about using or mounting rafts. But it would be stupid for PBO to go out and test it as if it was an unknown fact that needed to be discovered through experiment. That's what my first line said, in context.

Pete

 

[prv]

Prv in our defence I would say that Inflating a life raft in water is not something you normally do.

Not "normal" in that most of us haven't actually done it, fortunately. But yes, it is normal if you have to launch a raft. That's what the instructions tell you to do - check the painter is tied on, throw it overboard, pull the painter (lots of it, like ten metres or more) until it inflates, then board immediately. Do people imagine they are to throw it overboard and watch it sink, or do they simply not know how to use it at all? Seriously?

Pete

 

[fireball]

It's not stupid for someone to ask here if they really don't know. It's not stupid for PBO to mention it in an article about using or mounting rafts. But it would be stupid for PBO to go out and test it as if it was an unknown fact that needed to be discovered through experiment. That's what my first line said, in context.

Pete

You called it a stupid question - it's still not a stupid question - and whilst you believe you know the answer, is that in fact the case for all liferafts? Granted, it doesn't need to be a 3 page test, but some sort of response from the manufacturers or importers could form the content of a short article.
I can't go and measure my liferaft because I don't have one anymore - but it's an interesting thought - including at what depth (if any) they get negative buoyancy.

 

[pmagowan]

You called it a stupid question - it's still not a stupid question - and whilst you believe you know the answer, is that in fact the case for all liferafts? Granted, it doesn't need to be a 3 page test, but some sort of response from the manufacturers or importers could form the content of a short article.
I can't go and measure my liferaft because I don't have one anymore - but it's an interesting thought - including at what depth (if any) they get negative buoyancy.

Are you intending to abandon a submarine?

 

[J Neeves]

We buy rivets in Oz whose diameters are metric, say 3mm, but their length is in inches, say 3/8th".

I understand that when one's yacht is sinking, and especially if its doing this quickly, then the weight of a liferaft stored below appears to only be about 5kg but confess I cannot confirm this nor am likely to conduct tests.

Jonathan

 

[fireball]

Are you intending to abandon a submarine?

they do tend to sink quite frequently ...

 

[Heckler]

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

Pete

Hydrostatic, does it not mean that water pressure is needed to set it off?
So it needs to sink a bit?
S

 

[pmagowan]

Hydrostatic, does it not mean that water pressure is needed to set it off?
So it needs to sink a bit?
S

The relaease needs to sink a bit. The liferaft needs to float otherwise when it is released it will carry on down with the ship and never deploy.

 

[FishyInverness]

But it would be stupid for PBO to go out and test it as if it was an unknown fact that needed to be discovered through experiment.
Pete

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!

 

[bigwow]

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!

That's what happens when you get given a boat for free:encouragement:

 

[fireball]

The relaease needs to sink a bit. The liferaft needs to float otherwise when it is released it will carry on down with the ship and never deploy.

Hyrdostatic release allows the container to release from the cradle - quite handy if your boat has sunk or has turtled.

Whichever way you think about it - the liferaft only needs to float once it has inflated. Although it would be handy if it floated prior to inflation if it's been released from the cradle but nobody has operated the inflation mech.

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

 

[pmagowan]

Hyrdostatic release allows the container to release from the cradle - quite handy if your boat has sunk or has turtled.

Whichever way you think about it - the liferaft only needs to float once it has inflated. Although it would be handy if it floated prior to inflation if it's been released from the cradle but nobody has operated the inflation mech.

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

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.