what's the bouyancy of Carbon Fiber?

[Science Abuse]

I know it's light, but, when permiated totaly with its epoxy, how bouyant is it on its own? Anyone have an idea?

[Maro]

I would say that it isn't.....

[Farkas]

Wouldn't buoyancy be measured by the amount of volume an object can displace in order for it to float.. or something like that? I don't think you can just ask if carbon fibre is buoyant or not, it would depend what it is you're trying find out that's buoyant and what shape/size/weight it is.

[Maro]

I assumed a solid object..... a hull of carbon fibre would be boyant... a ball or brick would not.

[Linn1647545492]

they do make sailboat hulls out of CF so im sure its just a bouyant as fiber glass

[Farkas]

straight from wikipedia:

 

In physics, buoyancy is an upward force on an object immersed in a fluid (i.e. a liquid or a gas), enabling it to float or at least to appear lighter. Buoyancy is important for many vehicles such as boats, ships, balloons, and airships.

 

If the weight of an object is at least 3 percent less than the weight of the fluid the object would displace if it was fully submerged, then the object is less dense than the fluid and it floats at a level so it displaces the same weight of fluid as the weight of the object.

 

If the object has exactly the same density as the liquid, then it will stay still, neither sinking nor floating upwards, just as the liquid nearby stays still.

 

An object made of a material of higher density than the fluid, for example a metal object in water, can still float if it has a suitable shape (e.g. a hollow which is open upwards or downwards) that keeps a large enough volume of air below the surface level of the fluid. In that case, for the average density mentioned above, the air is included also, which may reduce this density to less than that of the fluid.

[Lustalbert]

To rephrase the question: what is the specific gravity of carbon fiber when cured vs. the constant of 1 (distiled water)

 

http://www.kynol.com/NewFiles/carbon%20fiber%20with%20pics.html

 

 

specific gravity, g/cm3

1.5 Novoloid

1.4

 

1.6 Pitch

1.5

 

1.8-1.9 Polyacrylonitrile

1.9-2.0

IIRC 1 cm3 of H2O is ~1 gram, so no, CF will not float.

 

This is just the carbon fiber, not taking into acount of the resin. That would be a function of the volume of the resin used, and its specific gravity to the volume of the carbon fiber in a given cm3. It make sense when I think about it, but I cant think of the formula (should be very simple, like an average)

Hopfully this is what you where looking for.

[Total Sign]

A lot of companies (Cigarette, Outerlimits, MTI) are doing kevar or carbon fiber reinforced hulls. Nothing new.

 

Very pricey. I was in Tennesse a few weeks ago for the offshore races, talked to Randy Scism of MTI, the 42' catamaran model un-rigged (No engines/drives/wiring) is 260k.

[Science Abuse]

A lot of companies (Cigarette, Outerlimits, MTI) are doing kevar or carbon fiber reinforced hulls.

You can make a hull out of concrete and it'll still float, thats not what I'm looking for. Basicaly I'm making something, and considering the materials whith which to make it. It will be small and solid. I want it to float, but barely. I'm looking for more of an iceburg then a bobber, and from what Andrew posted, CF may fit the bill, dependant on the bouyancy of the epoxy. I may just chip some off the basement floor, lord knows I've spilled plenty.

[Akula]

Bouyancy is determined by the weight of the water DISPLACED. It has alot to do with the shape, steel is negatively bouyant but somehow aircraft carriers float. If the weight of the water you are displacing is greater than the weight of the object displacing it, the object is bouyant. So, just asking if a material is bouyant isn't the best way to determine its use.

[Science Abuse]

Bouyancy is determined by the weight of the water DISPLACED. It has alot to do with the shape, steel is negatively bouyant but somehow aircraft carriers float.

It has nothing to do with the shape, the carrier floats because its full of air. It could be any shape you can imagine, as long as there's the same volume of air inside per ton of steel, it'll float. I'm talking about a solid hunk (or as solid as epoxied CF can be). I'm now thinking it wise to make it hollow, then to fill it water as balast, letting me tune its end buoyancy.

[El Karacho1647545492]

Buoyancy is entirely dependant on density of displacement. The reason a hull is buoyant is not because the fiberglass/steel/CF is light, its because the mass of the volume of water displaced is greater than the mass of the [material] + the mass of the air that does the displacing aka fills the void. Remember that density = mass/volume

 

So when a log floats downstream, thats because water hasn't permeated all the orifices and soaked through. If you go to the bottom of a stream, you'll find tons of wood at the bottom that has been soaked and rotted, thus lowering its density. So to answer the original question, you're probably gonna have to experiment. If you have a somewhat shapely piece of CF, you can determine its volume using cubic centimeters. Fortunately, as many of you know, one cubic centimeter = one milliliter. Therefore, you can get the volume of water you need. If the mass of the water is > 3% + the mass of the CF, it's buoyant.

 

Physics pwns joo.

[Akula]

Yeah, what would a scuba diving ex submariner know about bouyancy. The shape allows it to displace more volume of water than the equivalent hunk of metal. So saying the shape has nothing to do with it is inaccurate. The air in the carrier just happens to weigh less than the water being displaced by the volume of the cavity created by the steel. It is all about displacement, the shape allows for more or less displacement.

[Lustalbert]

Eric, do you have a highly acurate scale? Like for masuring grains of powder for reloading? If so, make a 1 cm3 block of CF with the resin of choice, and see how many grams it weighs. You may be able to adjust the consitency and see what it does. If you get it to weigh .9 grams or lower , it will be boyant.

[Science Abuse]

Yeah, what would a scuba diving ex submariner know about bouyancy. The shape allows it to displace more volume of water than the equivalent hunk of metal. So saying the shape has nothing to do with it is inaccurate. The air in the carrier just happens to weigh less than the water being displaced by the volume of the cavity created by the steel. It is all about displacement, the shape allows for more or less displacement.

If it was not full of air (or anything lighter then water), it would not float.

if it had the same volume of air per ton, it would float no matter what shape it was, and it would displace the same amount of water. The carriers shape is determined by, as with all boats, by what job it does, and the need to be straight and stable. A spher of equal mass and equal volume would displace just as much water, but would not be a good place to land planes.

 

Dive in a pool

do a cannonball into a pool

you'll displace the same water, no matter what shape you're in.