Waterbuoy

[fisherman]

If it's a chemical trigger, is it going to be the same as the tablet triggered lifejackets, which are susceptible to damp? If so you may find your pocket suddenly very full if you get wet. Two or three of them in various pockets and you might float upside down if you fell in.

It would need a 50 cm diameter float to lift 49kg, but it would be only just sub surface. In deep water the 50cm would be several times that size by the time it reached the surface, so would need to spill gas on the way up. One way round this is to contain the float in a net to limit its size, but then it would have to contain several atmospheres of pressure at the surface. We do this to get our pot marks up.

 

[KevB]

One litre of water weighs approx 1kg. A Mercury 3.5, 4 stroke outboard has a dry weight of 17kg so to stop the engine sinking you'd need a balloon holding just over 17 litres of air (3 petrol cans and a bit) in my opinion not very big.

The balloon only needs to displace more weight of water than the thing hanging off it weighs to keep the balloon on the surface.

Submarines for example use exactly this method, they either fill their tanks with water making the overall weight of the submarine heavier than the water it is displacing or fill the tanks with air from compressed air bottles to make the submarine lighter than the water it's displacing.

 

[KevB]

[ QUOTE ]
If I place a 1 kg lead weight in water (assume density ten times that of water) it will only displace 10% of its weight and would exert a net 900 gram downward force - the balloon would not pull this up.

[/ QUOTE ]

A balloon holding just over one litre of air will stop a 1 kg weight sinking because the air in the balloon would be displacing more than 1 kg of water so the balloon floats. Simple.

 

[Gludy]

I agree with those statements.
The volume of a sphere 50 cms diameter is approx 65.45 litres
Taking the weight of the air it contains as zero and assuming it weighs nothing then 45 kilo of steel at say an SG of 7 would have a volume of about 6.42 litres. In water it would have lift of 6.42 kilo so you would need to lift about 38.58 kilo with a balloon. (45 less it buoyancy of 6.43)So a balloon of 65 litres would manage it well.
These are large balloons to pack away into anything and the gas needed to fill them would also be pretty chunky as well!

Waterbuoy in the TV demo did not lift a one kilo weight - it simply gave enough lift to lift an air filled wooden box which only had a bit of negative buoyancy.
The weight in air is meaningless - the negative buoyamcy in water is the force we are talking about.

 

[neale]

We tested these in MBM some months ago. Using tins of beans at 450g each the ballon inflated and brought to the surface two tins (900g) in water around 3m deep.

I am not sure it matters about the weight of an object in water. They say it will support something that weighs 1kg and that it does.

My biggest issue at the time was that it took minutes, not seconds to inflate and bring the beans back to the surface. Apparently this has since been sorted but I have yet to see a modified one in operation.

Their bouyancy is soooooo much better than a cork keyring and un-inflated they are less obtrusive. I realised the hard way a few years back just how few keys a round ball of cork can keep afloat, it isn't many.

If the firing mechanism has been sorted now to operate quickly, I would defo have them on my important bits /forums/images/graemlins/blush.gif

 

[Gludy]

[ QUOTE ]
I am not sure it matters about the weight of an object in water. They say it will support something that weighs 1kg and that it does.


[/ QUOTE ]
The claim is illogical.
Cans of beans weighing 1 kg need a lot less power to lift than a lump of steel weighing 1 kg - both weigh the same but require different lifting powers. What really matters is the density and size of the object you are raising. Its weight in air in not the factor.
Basically you are overcoming negative buoyancy and it is this that matters.
A tiny baloon can lift a 100kg weight if the weight was a lump of plastic with an sg of 1.01. Yet the same baloon could not manage a 1 kg lump of tungsten with an SG of 19.
The uplifting force on a body in water equals the weight of water displaced and so the voulme is critical.
Waterbouy used an air filled box that was only just negative buoyancy and then claimed that the baloon could lift a 1 kg weight when it fact it could not - that baloon did not have the power to oivercome 1 kg of negative buoyancy.
Further - the speed at which the an object is lifted depends on the overall difference between its density and water.
In simplistic terms an object with an SG of 0.98 and one with an SG of 0.9 would come to the surface at very different speeds - one would be 5 times faster than the other as its the difference in buoyancy that matters.
The fact that the beans only came up very slowly indicates that you have only just overcome the negative buoyancy. So had the same weight been say a tin of spam with a higher SG it may not have made it up at all.

 

[Gludy]

[ QUOTE ]
I am not sure it matters about the weight of an object in water. They say it will support something that weighs 1kg and that it does.


[/ QUOTE ]
That is not right.
The reverse is true. /forums/images/graemlins/smile.gif
That is all that really matters the weight in air does not - the weight in water does.
A can of beans weighing 450 gms in air weighs a lot, lot less in water as the contents are almost the same density as water.

Imagine two cans - one sealed and full of bean sauce which has about the same density as water - imagine it weighs 450 gms in air. In water this may weigh just a few grams - basically the weight of the empty tin!!! That would be the downward force you are overcoming with the baloon - the weight of the empty tin!!!! So your test was meaningless.

Take the same tin that is empty but not sealed so it just fills with water - this tim weighs say 30 gms this would have the same downward pull as the tin filled with sauce with an SG of 1.

This is very important because the way waterbuoy presents itself leads people to believe that it can lift a 1 kg weight eg a 1 kg set of keys or an anchor weighing 1 kg - it cannot do this. I hope no magaizine is going to compound this misleading information and therefore continue the myth!!!?????

Try lifting a 1 kilo weight as used on w eighing scale - it will not do it.

 

[TigaWave]

I'm with you on this one Paul, very misleading for Joe public talking about weight it will lift. It has a level of positive bouyancy that will decrease with depth, which is a function of displaced water (its volume) and its mass.

It will overcome negative bouyancy which is less than its positive bouyancy at the given depth. Not an easy one to get across in a demo.

Nice idea though, but he could get into some horrible arguments with regard to how it is presented.

 

[KevB]

[ QUOTE ]
Try lifting a 1 kilo weight as used on w eighing scale - it will not do it.

[/ QUOTE ]


I'm having trouble agreeing with you. If I have 1kg of lead weight are you saying a balloon filled with just over 1 litre of air - i.e. will displace slightly more than 1kg of water, wont stop the 1kg lead weight from sinking?

 

[Gludy]

Kev
Can I first of all state that what i am stating is simple scientific fact, not an opinion.

At no time have I stated that the baloon is filled with a litre of air. In fact i have given examples proving what size baloon is required to lift a 45 kg anchor.

I will try to explain another way taking the misleading waterbuoy demo on TV.

They produced a large wooden box with a 1 kg label on it and I am sure it weighed 1 kg.
When they placed this large air filled box into the water is displaced a lot of water - this displaced water probably was almost a litre. Lets say it was 900 gms worth - in other words the box sank but had an sg of about 0.9 = 10% higher than water.
Now the force needed to lift this 100 gram force equates to 100 cc of iar. In practice more will be needed because there is also the weight of the gas cylinder and housing - say 150 cc size balloon.
So what you see in front of you is a baloon inflating and lifting a box with a 1 kg label on it BUT in fact only 150 gms of lift was required to do it.

Now if they had taken an iron weight of one KG with say an SG of 7 then the volume of water displaced by this weight would be 1000/7 = 142cc.
So the 1 kg weight would have positive buoyancy of 142 gms giving a net downward force of 858 gms. Therefore instead of the 150 gms of lifting force needed someting almost 6 times bigger would be needed - 875 gms yet both items being lifted weighed the same when out of water.
So all that matters is what the 'weight; in water is and to get that you have to deduct the volume of water displaced by the weight from the weight.


Got it? /forums/images/graemlins/smile.gif

 

[Gludy]

[ QUOTE ]
Nice idea though, but he could get into some horrible arguments with regard to how it is presented.

[/ QUOTE ]
You can forget the effect of depth to try and keep it simple.
What these items should carry - which the USA version does is the lifting force they can lift or the weight of a set of keys they can lift.
However this lifting weight for keys would not lift a lump of lead weighing the same weight because lead has a higher density then steel and so displaces lees water for a given weight = less postive buoyancy.

I actually invented a whole range of fly fishing products including the fastest sinking lines in the world etc and used tungsten to produce the sinking forces and super postive bouyancy fly lines - I had the same agruments then!! /forums/images/graemlins/smile.gif

 

[rickp]

What do you think the radius of the balloon was? Judging from Theo's hand - could it be 7cm? That would give it a volume of over 1 litre, wouldn't it? I think its certainly greater than 3cm (your 150cubic cm).

Rick

 

[MapisM]

[ QUOTE ]
The claim is illogical.

[/ QUOTE ]That's a very kind statement of yours.
Reading such claim in a boating forum is actually surrealistic, to say the least.
I wonder how anyone thinking along these lines can dare to use boats weighing some tons.
/forums/images/graemlins/laugh.gif

 

[neale]

OK but the point is that if it would lift two cans of beans (900g weight in air), then it will lift your keys, a mobile phone, a handheld VHF, a handheld gps, a pair of binos or any other small item that you may be worried about dropping overboard.

I'll bear in mind your comments and make sure that if I ever feel the need to take a solid 1kg lump of metal onto the boat that I can in no way afford to lose, I'll stick two waterbouys on just in case /forums/images/graemlins/tongue.gif

 

[Gludy]

You only have to look at the size of the one KG weight to see how high the volume was. In water i do not think the balloon would have been a litre.
Imagine that weight instead of being a large box filled with air as being a sinle iron weight - it would not have done it. That is why they made into a large box!!!

All I am stating are simple facts - is anyone disputing the simple science?
if so they can argue with Archimedes
/forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[Gludy]

Mapism
You are not disoputing the scientific facts are you?

Boats displace enough weight of water to conterect their downward weight - most of the inside is air - if you fill this with water you sink!!!! /forums/images/graemlins/laugh.gif

Even forums have to accept simple science.

What i am staing has been understood for thousands of years and is taught in almost year one lesson one in physics.

 

[Gludy]

[ QUOTE ]
OK but the point is that if it would lift two cans of beans (900g weight in air), then it will lift your keys, a mobile phone, a handheld VHF, a handheld gps, a pair of binos or any other small item that you may be worried about dropping overboard.


[/ QUOTE ]
it would lift a normal bunch of keys - they only used a small bunch of course.
It may not lift a large bunch.

It depends on how much pressure they can put inside the submerged balloon and that depends on the gas cylinder size which has to be very small.

They only used a small bunch of keys.

All I sm stating time after time is that the one kg test was totally misleading and there is no way it can lift a 1 kg bunch of keys.

Secondly that test with tins of beans are misleading - use a weight from a set of weighing scales for a fair test as the SG of this is closer to the itmes attached to such a device.

I am finding it difficult to accept that anyone could be disputing the science of this matter /forums/images/graemlins/laugh.gif
[ QUOTE ]
I'll bear in mind your comments and make sure that if I ever feel the need to take a solid 1kg lump of metal onto the boat that I can in no way afford to lose, I'll stick two waterbouys on just in case

[/ QUOTE ]
Then you would have been misled and lose the 1 kg item because I do not think that the lifting ability of the waterbuoy is even 500grms.
You are proving my point for me! The test was misleading and people cam fall for it and hence lose things!
UNLESS the item weighing 1 kg was as large as that enourlose box they ised - it would not work.
How many people carry oround boxes of that size in their pockets????? /forums/images/graemlins/laugh.gif
You would probaly need 6 waterbouys to lift a 1 kg weight and so spend 3100 on them!!!

 

[rickp]

[ QUOTE ]
You only have to look at the size of the one KG weight to see how high the volume was.

[/ QUOTE ]

Yes, not disputing that. What I wanted to know was your opinion of the balloon size. Just as KevB asked, but you ignored.

I think the balloon is large enough to hold one litre - but there's only one way to find out....

Rick

 

[neale]

I'll telll you what, leave it with me and I will see if I can get a couple more to retest.

I'll test them with a solid 1kg lump of metal, and try different depths including 'quite deep' to see what happens.

Now, where did I leave my stash of gold ingots??? /forums/images/graemlins/grin.gif

 

[Gludy]

Rick the ballon has to be a litre underwater and that depnds on the amount of gas pushed into it. Underwtaer the baloon size was nowhere nerar a litre.

Ia m not ignoring the point - I am stating simple facts, nio opinions and am amused and amazed at the resistance to these simple facts.

The bal;oon only just managhed to lift up the Ikg box of that size - that box was a low denisty becayse of its size,. a 1 kg weight would be maybe 6 times or more smaller and hence require six or seven times the lifting power. Its that simple.

Are you disputing this????????