Would it sink or would it float?

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spark
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A concrete cube 3m size with cinder block walls:

http://www.csgnetwork.com/specificgravmattable.html
specific gravity of gravel concrete = 2403 kg/m3 = 2.403 g/cm3

http://www.engineeringtoolbox.com/specific-gravity-liquids-d_336.html
specific gravity of sea water = 1.028 g/cm3 = 1028 kg/m3

buoyancy of a 3m cube in sea water is: 3m X 3m X 3m X 1028 kg/m3 = 27756 kg

cinder blocks are 6” X 6” x 12” . A cinder block wall is 6” thick. 1” = 2.5 cm, 6”= 15 cm = 0.15 m
5 walls for the cube: the top is open.

weight of the walls = 3m X 3m X 0.15m X 2403kg/m3 X 5 = 16220 kg

buoyancy – weight = 27756 kg – 16220 kg = 11536 kg.

buoyancy weight ratio = 16220 / 27756 = 0.5844 = 58.44%

So the cube would float and about 58 % of it would be in the water.
58% of 3m is 1.75m The cube would float and 1.75m of it would be below the water line, 1.25m would be above.
3m=10′ 1.75m=5’9” 1.25m=4’3” approx

1 Meter = 3.2808399 Feet

#22899

Anonymous

First, get your materials straight. You talk of cinder blocks and concrete. Cinder blocks are not made of gravel concrete, they are made with cinders, they don’t weight as much and don’t cost as much and are not as durable as concrete blocks. Cement blocks are even denser, to point of being airtight, but they aren’t common.

You didn’t allow for any steel to take the tension in the middle of the walls, cement and concrete do not take much tension to crack, and cinders are far worse. Besides, you will need another couple 100 lbs to skim coat it to make it watertight, or heavy paint.

This sort of “engineering” is scary.

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