Buoyancy Aid Testing.
Mike Parsons
Minimum buoyancy Lead weight Iron or steel weight Cast iron weight
50N 5.5kg 5.7kg 5.8kg
45N 4.9kg 5.2kg 5.2kg
40N 4.4kg 4.6kg 4.6kg
35N 3.8kg 4.0kg 4.1kg
I need to raise the subject of weights for buoyancy aid testing at a
meeting and need to understand the facts before I confuse myself and
the meeting!
PHYSICS
-------
[Source Wikipedia
The newton is the unit of force derived in the SI system; it is equal
to the amount of force required to accelerate a mass of one kilogram
at a rate of one metre per second per second.]
Why buoyancy is measured in Newtons?
What is buoyancy?
For each row is the
Mass of weight different because each material has a different
density?
and
Each weight has the same volume and therefore displaces the same
amount of water?
WEIGHTS
-------
Does any Group near Heathrow / West London have or know of a source of
a set weights for testing buoyancy aids?
Thanks.
Mike
O. Level Physics 1965 which I seem to have forgotten a lot of the
subject and pre SI Units.
Stephen Rainsbury
news:ve4kf55b9tprm3r9g...@4ax.com...
> Weights for Buoyancy Aid Testing - 50N Standard
>
> Minimum buoyancy Lead weight Iron or steel weight Cast iron weight
> 50N 5.5kg 5.7kg 5.8kg
> 45N 4.9kg 5.2kg 5.2kg
> 40N 4.4kg 4.6kg 4.6kg
> 35N 3.8kg 4.0kg 4.1kg
>
>
> I need to raise the subject of weights for buoyancy aid testing at a
> meeting and need to understand the facts before I confuse myself and
> the meeting!
>
> PHYSICS
> -------
>
> [Source Wikipedia
>
> The newton is the unit of force derived in the SI system; it is equal
> to the amount of force required to accelerate a mass of one kilogram
> at a rate of one metre per second per second.]
>
> Why buoyancy is measured in Newtons?
> What is buoyancy?
Different definitions apply, in this case I would take it to mean the total
force when you have considered your weight (down), upthrust (up) and
bouyancy (up)
> For each row is the
>
> Mass of weight different because each material has a different
> density?
Don't know why its like that.
Density of lead = 11.35 g/cc
Density of Iron = 7.874 g/cc
so that doesn't fit.
> and
>
> Each weight has the same volume and therefore displaces the same
> amount of water?
If the volume is the same then yes, and the mass of water displaced x 9.81
gives you the upthrust in newtons.
--
Stephen Rainsbury (Physics teacher - but doesn't understand the table - but
then its early and I havn't slept due to a dental problems)
DESC Gillingham, Kent
www.gillinghamscouts.org.uk
John Russell
>"Mike Parsons" <m...@codfish.co.uk> wrote in message
>news:ve4kf55b9tprm3r9g...@4ax.com...
>> Weights for Buoyancy Aid Testing - 50N Standard
>>
>> Minimum buoyancy Lead weight Iron or steel weight Cast iron weight
>> 50N 5.5kg 5.7kg 5.8kg
>> 45N 4.9kg 5.2kg 5.2kg
>> 40N 4.4kg 4.6kg 4.6kg
>> 35N 3.8kg 4.0kg 4.1kg
<snip>
>> For each row is the
>>
>> Mass of weight different because each material has a different
>> density?
Yes
>Don't know why its like that.
>
>Density of lead = 11.35 g/cc
>Density of Iron = 7.874 g/cc
>
>so that doesn't fit.
That fits perfectly. A 5.5kg lead weight is 0.48 litre volume. A 5.7kg
iron weight is 0.72 litre. So the iron weight displaces 0.24 litres more
water than the lead weight, giving additional buoyancy of about 0.24kgf -
hence the difference in round numbers between 5.5 and 5.7.
>> and
>>
>> Each weight has the same volume and therefore displaces the same
>> amount of water?
No - the weights are different because the volumes are different and hence
displace different amounts of water.
>If the volume is the same then yes, and the mass of water displaced x 9.81
>gives you the upthrust in newtons.
--
John Russell
CSL 1st Pinhoe Exeter Devon
http://www.pinhoescouts.org.uk/cubs/
Cubs don't care how much you know, but they need to know how much you care.
Ewan Scott
>
> Minimum buoyancy Lead weight Iron or steel weight Cast iron weight
> 50N 5.5kg 5.7kg 5.8kg
> 45N 4.9kg 5.2kg 5.2kg
> 40N 4.4kg 4.6kg 4.6kg
> 35N 3.8kg 4.0kg 4.1kg
>
>
> I need to raise the subject of weights for buoyancy aid testing at a
> meeting and need to understand the facts before I confuse myself and
> the meeting!
>
>
> Does any Group near Heathrow / West London have or know of a source of
> a set weights for testing buoyancy aids?
>
Not near Heathrow, but no I don't.
We test out boats on a regular basis - every time they capsize...
The buoyancy aids get inspected to make sure that they have all their straps
and clips working and that they don't have holes and that the zips don't
stick. As for their ability to carry a load - We have never tested them
against set weights. If they can hold the wearer in the water then they must
be up to scratch.
On the subject of testing. Be careful of going down a too technical road.
There is, when it comes to testing safety critical equipment, a definition
somewhere of who a competent person is. And to satisfy test requirements the
test needs to be carried out by a competent person. The competent person
puts his name against the safety of the equipment... I guess you probably
know that but nonetheless, it is worth a thought. And sorry. I'm not going
trawling to find the definition but when talking about testing the term
"competent person" keeps cropping up.
Ewan Scott
fred
> Minimum buoyancy Lead weight Iron or steel weight Cast iron weight
> 50N 5.5kg 5.7kg 5.8kg
> 45N 4.9kg 5.2kg 5.2kg
> 40N 4.4kg 4.6kg 4.6kg
> 35N 3.8kg 4.0kg 4.1kg
> I need to raise the subject of weights for buoyancy aid testing at a
> meeting and need to understand the facts before I confuse myself and
> the meeting!
Why?
> Why buoyancy is measured in Newtons?
Because it's a force, so it's measured in newtons. If you hung a 5kg
weight from the bottom of a jacket in air the weight would exert a
force of 49Newtons as force=mass*acceleration 49N= 5kg * 9.8m/s/s and
9.8 is the acceleration due to gravity. If the weight was in the water
it would have the same mass, 5kg but would exert less force as the
water would be providing some support.
> What is buoyancy?
from wikipedia
"In physics, buoyancy (pronounced /ˈbɔɪ.ənsi/) is the upward force
that keeps things afloat. The net upward buoyancy force is equal to
the magnitude of the weight of fluid displaced by the body. This force
enables the object to float or at least seem lighter. - Wikipedia "
> For each row is the Mass of weight different because each material has a different
> density?
> and
> Each weight has the same volume and therefore displaces the same
> amount of water?
From Wikipedia
"Suppose a rock's weight is measured as 10 newtons when suspended by a
string in a vacuum. Suppose that when the rock is lowered by the
string into water, it displaces water of weight 3 newtons. The force
it then exerts on the string from which it hangs would be 10 newtons
minus the 3 newtons of buoyant force: 10 − 3 = 7 newtons"
So
for the 50N jacket with leadthe weight specified is 5.5Kg
the density of lead is 11340 Kg/m3
density = mass/volume therefore as we know the lead will be fully
submerged the volume it will take up is volume=mass/density =
0.000485m3
as water has a density of 1000kg/m3 the same equation
volume = mass/density or mass = density x volume gives 0.485 kg
so a 5.5kg lead weight in water will exert the same force as a 5.012kg
weight in air as 5.5-0.485kg = 5.012kg
5.012 kg hanging from the bottom of your life jacket would be
equivalent to 49 Newtons (F=m*a 49N=5.012*9.8)
for the 50N jacket with cast iron the weight specified is 5.8Kg
the density of lead is 7800 Kg/m3
density = mass/volume therefore as we know the lead will be fully
submerged the volume it will take up is volume=mass/density =
0.000743m3
as water has a density of 1000kg/m3 the same equation
volume = mass/density or mass = density x volume gives 0.783 kg
so a 5.8kg cast iron weight in water will exert the same force as
5.017kg in air as 5.8-0.783kg or 5.017kg
5.017 kg hanging from the bottom of your life jacket would be
equivalent to 49 Newtons (F=m*a 49N=5.017*9.8)
I hope this makes sense, now just to confuse the issue cast iron
density can vary between 6800-7800kg/m3, water density can vary with
pressure, composition, salinity & depth and acceleration due to
gravity can very with latitude, but non of these are enough to be
important.
> WEIGHTS
> -------
>
> Does any Group near Heathrow / West London have or know of a source of
> a set weights for testing buoyancy aids?
fs120603.pdf states "Weights can be manufactured locally using this
chart." I would be interested to hear from anyone who has had this
done as unless you know someone and can get "mates rates" I suspect it
would be very expensive.
So anyway back to my first question why do you need to test the
buoyancy aids?
The fact sheet specifies that they must be inspected, it describes a
test:
"A simple test for a lifejacket or buoyancy aid is to hang on an
appropriate weight, squeeze out all the air and see if it floats. If
it does float it is OK.
If it fails to float it needs replacing. (See chart on page 7)"
but doesn't insist this is done. This test seems appropriate to the
early 1980's when I was a scout and we used "life jackets" with rigid
foam blocks & extra air inflation in case of emergencies but doesn't
seem particularly relevant to modern buoyancy aids with flexible
closed cell foam.
In 26 years of sailing & teaching sailing safely I have only ever
conducted one buoyancy test (using a brick) to prove to a friend that
his ancient but beloved buoyancy aid was as unsafe as everyone else
could see it was. Anybody with enough experience to get a coaching
qualification or water sports authorisation should be able to inspect
a buoyancy aid & determine if it is safe without trying to sink it. I
have recently had to get a new one after using mine very regularly for
5 years because of a broken zip, the buoyancy was fine (tested by
pitch poling a catamaran in a force 6 this summer). In a modern
buoyancy aid the flotation is going to outlast the outer material,
zips fasteners & stitching.
John Russell
>> Does any Group near Heathrow / West London have or know of a source of
>> a set weights for testing buoyancy aids?
>fs120603.pdf states "Weights can be manufactured locally using this
>chart." I would be interested to hear from anyone who has had this
>done as unless you know someone and can get "mates rates" I suspect it
>would be very expensive.
A length of scrap angle iron with a hole drilled through it (for the cord)
wouldn't be expensive.
John Russell
>On the subject of testing. Be careful of going down a too technical road.
>There is, when it comes to testing safety critical equipment, a definition
>somewhere of who a competent person is. And to satisfy test requirements the
>test needs to be carried out by a competent person. The competent person
>puts his name against the safety of the equipment...
Does he? I doubt it. I bet what he does is sign that it passed the test.
That's a question of fact.
Dave
"John Russell" <jrus...@jrrconsulting.co.uk> wrote in message
news:as0lf5la8n0dbjmn1...@4ax.com...
> Ewan Scott wrote:
>
>
>>On the subject of testing. Be careful of going down a too technical road.
>>There is, when it comes to testing safety critical equipment, a definition
>>somewhere of who a competent person is. And to satisfy test requirements
>>the
>>test needs to be carried out by a competent person. The competent person
>>puts his name against the safety of the equipment...
>
> Does he? I doubt it. I bet what he does is sign that it passed the test.
> That's a question of fact.
>
Fact possibly based on the fact that you knew what you were doing when you
tested it.
Competent to carry out the test.
DaveB
West Yorks
Ewan Scott
>
>
>>On the subject of testing. Be careful of going down a too technical road.
>>There is, when it comes to testing safety critical equipment, a definition
>>somewhere of who a competent person is. And to satisfy test requirements
>>the
>>test needs to be carried out by a competent person. The competent person
>>puts his name against the safety of the equipment...
>
> Does he? I doubt it. I bet what he does is sign that it passed the test.
> That's a question of fact.
>
still need to be, I'm guessing, a competent person. It is only when you
start seeking the definition of competent person that the lack of clarity
becomes, well... clear :-)
So, the week after the BAs were tested and passed by a competent person, one
of them fails in some way, where then would that leave the tester? Wasn't
me guv', they was allright when I checked them and put them back in the
stores?
The whole concept of testing the kit has to be superficial. A visual check,
and does it work in use? It's a bit like the boat test - which was surely
designed for osmosis prone GRP boats. With Rotomoulded plastic boats they
only leak if they have holes and they generally all come equipped with the
required buoyancy. A visual inspection should show that the buoyancy is all
in place, the seat is secure, the footrests are secure and that there are
proper lifting points etc.. ( We did have one boat which had a leak. It
would still have passed the floatation test. We traced the leak by putting
the boat on trestles and filling it with water).
Ewan Scott
Ewan Scott
> fred wrote:
>
>
>>> Does any Group near Heathrow / West London have or know of a source of
>>> a set weights for testing buoyancy aids?
>>fs120603.pdf states "Weights can be manufactured locally using this
>>chart." I would be interested to hear from anyone who has had this
>>done as unless you know someone and can get "mates rates" I suspect it
>>would be very expensive.
>
> A length of scrap angle iron with a hole drilled through it (for the cord)
> wouldn't be expensive.
>
How deep would the water you test with the angle iron need to be?
Sorry, I think a visual inspection every time the kit is used should be
sufficient.
Okay, how do you test that helmets are still up to standard?
Ewan Scott
John Russell
>
>"John Russell" <jrus...@jrrconsulting.co.uk> wrote in message
>news:co0lf59ao5ggb0aum...@4ax.com...
>> fred wrote:
>>
>>
>>>> Does any Group near Heathrow / West London have or know of a source of
>>>> a set weights for testing buoyancy aids?
>>>fs120603.pdf states "Weights can be manufactured locally using this
>>>chart." I would be interested to hear from anyone who has had this
>>>done as unless you know someone and can get "mates rates" I suspect it
>>>would be very expensive.
>>
>> A length of scrap angle iron with a hole drilled through it (for the cord)
>> wouldn't be expensive.
>>
>How long is the required length of angle iron? :-)
>
>How deep would the water you test with the angle iron need to be?
A bit of 6" I-beam (to BS4) 13.5" long would be just right. If you drilled
two holes at opposite ends, for two cords, you could do the test in your
bath.
John
Ewan Scott
>>> A length of scrap angle iron with a hole drilled through it (for the
>>> cord)
>>> wouldn't be expensive.
>>>
>>How long is the required length of angle iron? :-)
>>
>>How deep would the water you test with the angle iron need to be?
>
> A bit of 6" I-beam (to BS4) 13.5" long would be just right. If you
> drilled
> two holes at opposite ends, for two cords, you could do the test in your
> bath.
>
After the bollocking I got for soaking withies in the bath for lantern
making, if I were to suggest dangling a lump of rusty iron in the bath I
wouldn't live to tell the tale! :-)
Ewan Scott
John Russell
>After the bollocking I got for soaking withies in the bath for lantern
>making, if I were to suggest dangling a lump of rusty iron in the bath I
>wouldn't live to tell the tale! :-)
But you'd only have to live long enough to sign the test certificate!
Graham Drabble
news:lqudnfI8M-E9WmfX...@bt.com:
Whatever for?
Next you'll be telling me you're not allowed to wash rope in the
washing machine either!
--
Graham Drabble
1st Uxbridge
http://www.drabble.me.uk/
fred
> >news:co0lf59ao5ggb0aum...@4ax.com...
> >> fred wrote:
>
> >>>> Does any Group near Heathrow / West London have or know of a source of
> >>>> a set weights for testing buoyancy aids?
> >>>fs120603.pdf states "Weights can be manufactured locally using this
> >>>chart." I would be interested to hear from anyone who has had this
> >>>done as unless you know someone and can get "mates rates" I suspect it
> >>>would be very expensive.
>
> >> A length of scrap angle iron with a hole drilled through it (for the cord)
> >> wouldn't be expensive.
>
> >How long is the required length of angle iron? :-)
>
> >How deep would the water you test with the angle iron need to be?
>
> A bit of 6" I-beam (to BS4) 13.5" long would be just right. If you drilled
> two holes at opposite ends, for two cords, you could do the test in your
> bath.
>
> John
>
> --
> John Russell
> Cubs don't care how much you know, but they need to know how much you care.
OK I didn't think of that, but you would need 4 pieces 1 each for the
different standard BAs to be tested.
Anyway the people here will supply I bean for £25 a meter & even cut
it to length for you
Ewan Scott
> Ewan Scott wrote:
>
>
>>After the bollocking I got for soaking withies in the bath for lantern
>>making, if I were to suggest dangling a lump of rusty iron in the bath I
>>wouldn't live to tell the tale! :-)
>
> But you'd only have to live long enough to sign the test certificate!
>
Ewan Scott
MatSav
news:RLGdnSMRHq9G8WfX...@bt.com...>> Weights for Buoyancy Aid Testing - 50N Standard
Indeed. There are a few problems with the requirements of the
Fact Sheet. The mass of the test weights listed doesn't give any
tolerance, class, or uncertainty of the required
value. The form of the weights isn't defined. The test method
isn't given in detail.
One method of proving the competency of the tester is by using a
UKAS accredited test house. A few years ago, I researched if
there was a test house that could offer such a service. I found
one UKAS accredited laboratory that could test and certify the
bouyancy aids. My Group chose not to use their service, as the
p&p plus testing cost would be greater than buying new bouyancy
aids.
I've just checked the UKAS web site, and there isn't a test house
listed for that service any more.
I doubt that there are many Groups who apply this requirement
thoroughly. I try to comply through self-testing, with two
cast-iron test weights marked as 5kg and 2lb - which is actually
more than the 5.8kg given - but is within 2%.
In 20 years of self-testing bouyancy aids, I've only failed two
because they failed the flotation test. As others have said,
there's a visual inspection before each use.
(Mike, I can loan you my test weights if it helps).
--
MatSav
Broooz
>
> That fits perfectly. A 5.5kg lead weight is 0.48 litre volume. A 5.7kg
> iron weight is 0.72 litre. So the iron weight displaces 0.24 litres more
> water than the lead weight, giving additional buoyancy of about 0.24kgf -
> hence the difference in round numbers between 5.5 and 5.7.
A bit precise for my liking. When someone told me my bouyancy aid was from
the ark and would not support me anymore I tested it using a large rock in a
swimming pool - not sure the janny was very keen but it worked ok. I think
it was 5kg. 10 years has passed and I still have that BA - wonder if it
would still pass. Not long to take the risk as wife getting me a new one
for xmas.!
Brian Smith
<84d04cb9-1602-44d5...@n35g2000yqm.googlegroups.com>,
fred <r1234...@aol.com> writes
--
Brian
www.8thmuswellhill.org.uk
Mike Parsons
wrote:
Thank you all for all advice. I am now able to impress everybody at
the meeting with my newly discovered knowledge of physics.
Mike
Mike Parsons
Matt
Thanks.
I have asked our parents for help with the weights and will keep you
informed of any progress.
Mike