How do i build a cement boat?
 

I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??

On 29 Apr 2005 05:11:37 -0700, wrote:

I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??

Use a vacuum pump to press a thin cement shell - some fiber content
would be helpful - is this disallowed?

Brian Whatcott Altus, OK

I'm pretty sure that that's disallowed :-(

Interesting project. A model Ferocement boat.

Portland cement and 60-70 seive sand will make a strong fine grained
plaster. You will have to experiment with the ratio but about 4 parts sand
to 1 part cement should work. It needs to be a very stiff mix so add water
sparingly. For reinforcing I think you have two options. You can use a
chopped fiberglass available from any ready mix supplier and occasionally at
Home Despot or a fine (.016") wire 20x20 plain steel mesh available from
McMaster for about $1.50/sq.ft. If you go to your local ready mix plant
and explain what you are doing they will either laugh you out of the office
or get interested and give some good advice and maybe even a quart of cement
and some fiber.

You will need a form. Styrofoam will work but you will need to seal it well
to prevent it from sucking water out of the mix. A wood form would be
better but harder to shape. Mount the form on a painted board and apply a
thin coat of grease.

If you use mesh, shape it around the form and staple it lightly in place
around the edges only. Smear on the cement mix and work it in well to a
thickness of about 3/8". (assuming a total volume of 1 cu.ft.) If using
fiber it should probably be a little thicker.

The key is to make the cement mix as dense as possible. As Brian said, a
vacuum will help the ultimate strength a lot. You can make a bag from 4mm
poly sheet folded over and sealed at the edges. Make it about twice the
size of the board so that it fits very loosly over the mold. You don't want
it to stretch over the top or it will thin out the cement. You can use
nylon tube and one of those plastic suction cups used to stick things to
windows for a vacuum port. Drill through the middle and fit the tube
tightly in the hole. Borrow a vacuum pump and suck the bag down as tight as
possible.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

wrote in message
oups.com...
I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??

I'm pretty sure that that's disallowed :-(

Check and make sure. Cement has very little tensile strength. You really
can't build a thin shelled cement structure without some reinforcement.
Glass fiber is denser than water so it will not add any buoyancy.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

In article , betwys1
@sbcglobal.net says...

You need to check out more and define more.

Cement can be rocks held together by portland cement, or by ply
_cemented_ by epoxy glue. Or by portland cement reinforced with glass
fibre. Vass deferences.

You really need to look for more info and provide it. A lot can be done,
but not without full info.

"concrete pavement is sometimes referred to as cement; "they stood on
the gray cement beside the pool"
a building material that is a powder made of a mixture of calcined
limestone and clay; used with water and sand or gravel to make concrete
and mortar

something that hardens to act as adhesive material

make fast as if with cement; "We cemented our friendship"

cover or coat with cement

any of various materials used by dentists to fill cavities in teeth
cementum: a specialized bony substance covering the root of a tooth
bind or join with or as if with cement
www.cogsci.princeton.edu/cgi-bin/webwn

************************************************** **********************
the general sense, a cement is any material with adhesive properties.
************************************************** *******************
The term cement is also commonly used to refer more specifically to
powdered materials which develop strong adhesive qualities when combined
with water. These materials are more properly known as hydraulic
cements. Gypsum plaster, common lime, hydraulic limes, natural pozzolana
and Portland cements are the more common hydraulic cements, with
portland cement being the most important in construction. "


I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??

Use a vacuum pump to press a thin cement shell - some fiber content
would be helpful - is this disallowed?

Brian Whatcott Altus, OK




--
Do M$oft actually _refer_ to _users_
when they design their UIs? The increasing
"ease of use" seems more and more like
fascism every time!

In article 2qqce.320$qV3.29@lakeread04, says...

I'm pretty sure that that's disallowed :-(

Check and make sure. Cement has very little tensile strength. You really
can't build a thin shelled cement structure without some reinforcement.

Glass fiber is denser than water so it will not add any buoyancy.

But enormous strength.........

--
Do M$oft actually _refer_ to _users_
when they design their UIs? The increasing
"ease of use" seems more and more like
fascism every time!

In article .com,
says...

I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??

What does the 1 cubic foot refer to? The volume of cement or the capacity of
the boat? If the later, that's a really small boat!

On Fri, 29 Apr 2005 05:11:37 -0700, iceman390 wrote:

I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??

Can you add aggregate to the cement? Can you use chicken wire or some
other metal wire material? When concrete (aggregate + cement) is used for
structural purposes it is usually reinforced with bar material of some
sort. And cement is usually mixed with some type of aggregate.

Is this a university competition? Is there a website with the full rules?

--Mac

Usually cement boats are made by trowling mortar into a mesh form.

For a quick and cheap alternative, mix your cement and soak burlap in it.
Lay the soaked buralp over a form which could be made of wood, paper mache
covered in plastic, wet sand, or whatever. Cover the whole thing with
plastic for a few days until the cement cures. Then lift your boat hull
off the form.

Cheap durable house walls have been made in Africa by draping burlap soaked in
cement over wires stretched between poles. You might find something about
it on the Internet.

) writes:
I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??



--
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William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-FreeNet email must have "notspam" in subject or it's returned

There's been a lot of discussion about materials and techniques. I suggest
that regulars on this forum will be of limited assistance with these
"engineering" aspects of the problem.

The hull design, on the other hand, is an interesting question.

The boat must float with a heavy load, presumably at rest in a smooth pool,
and have a maximum volume of 1 cubic foot. How will the weight be
measured? I would guess, by adding small blocks or balls of cargo, until a
gunwale goes under, and the craft sinks.

Will the cargo be very dense, such as lead blocks? In that case, you will
want the weight to be concentrated at the bottom center, as ballast. A very
deep hull, (ideally a longish cylindrical shape, with one end closed - as
you add weight, stability increases.) On the other hand, if it's too deep a
hull, it will lack stability when unballasted, and perhaps fail at the
outset.

If the weight to be added is a relatively light (low-density), the hull
shape would be very different, perhaps towering above the gunwales.
Stability will be a limiting factor. Perhaps a catamaran form? What about a
"floating drydock" approach, where the cargo is on a platform at the BOTTOM
of two (sealed?) pontoons - as it is loaded, the platform will submerge, and
cargo will contribute to the buoyancy...

--
Sal's Dad


wrote in message
oups.com...
I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??

I am more concerned with the design of the hull. This is a project for
my High School Engineering class, and our teacher wants us to use only
cement to get our craft to float.

we can use some sort of mesh or something to get the cement to hold a
shape, but it cannot be wood, or something else that would provide
buoyancy that way.

There certainly are lots of cement barges plying the costal rivers of China.
Staight sides and flat botton, but probably for ease of construction and
load handling.

Might want to play with the math a little to get a fix on the shape that
encloses the greatest volume with the least surface area. Hmmm. Sounds a lot
like half a sphere. Could cast it inside a basketball...

surfnturf


"No Spam" wrote in message
news:UTeee.7459$Rl6.7151@trndny08...

I think I would model it after river barges. very flat bottom, straight
sides and rounded up at both ends. Rectangle shape. It is used to haul
tons of coal around here every day. It is also a very simple shape to
produce. Also agree with everyone else that you need a mesh inside to
keep it all together.

On Wed, 04 May 2005 05:40:12 -0700, iceman390 wrote:

we can use some sort of mesh or something to get the cement to hold a
shape, but it cannot be wood, or something else that would provide
buoyancy that way.

Use chicken wire, then.

Make the boat a simple sqare box maybe half an inch thick.

You'll have to work out how big each side is based on your cu. ft. limit.

Since it is a school project, I won't say much more than that. Come to
think of it, I'd probably lead you in the wrong direction anyway since
I've never had any training as a marine architect.

Good luck!

--Mac

OK, as I understand it you need to carry as much cargo as possible in a boat
of 1728 cubic inches total volume, can use some reinforcement as long as it
doesn't float and obviously it has to be cheap. Here is another idea.

As others have said a barge shape would be most efficient. It is easy to
make and has a lot of innitial stability. Now for a little math. Fresh
water weights 62.5 pounds per cubic foot so that is the maximum total
weight. You must have some freeboard above the water line so there is a
practical limit somewhat lower than that. Concrete made with portland
cement and sand weighs about .087 pounds per cubic inch. A thickness of
3/8" weights .0326 pounds per square inch.

The shape that will inclose the largest volume with the least amount of
material is a sphere. In this case, half a sphere 14 7/8"" in diameter.with
a surface area of 347.5 sq.in.weighing 11.33 pounds would be the most
efficient but it would not be stable. Next choice is a topless cube 12" on
a side with a surface area of 720 sq. in. and a weight of 23.5 pounds.
Still not very stable though.

An interesting thing about a topless cube though. If you split it in half
and lay the halves side by side you get the same volume without increasing
the surface area. Any other combination of H*W*L with the same volume
increases the surface area. Squash the cube so it is 6" high, 24" long and
12" wide. Now the same cubic foot volume still has a surface area of 720
sq. in. and weights 23.5 pounds but is a lot more stable. In fresh water it
will sink when about 39 pounds of cargo is very evenly loaded. If you are
feeling real lucky you can try for 1/4" thick cement and save about 7 pounds
but it will be very delicate.

To build it, make a block 23 1/4" long by 11 1/4" wide by 5 5/8" high. You
will need some "draft" to be able to remove the block once the cement sets
so taper the sides so the bottom is about 1/4" wider than the top and take
your measurements half way up. Coat it with some heavy grease. Cover it
with hardware cloth or mix some concrete fiber reinforcing in the cement..
Spread on the cement 3/8" thick and work it into the hardware cloth well.

If you are going to try for 1/4" thick, increase the size of the block to 23
1/2" x11 1/2" x 5 3/4" and cut some grooves in the top about 3/8" deep and
1" wide for stiffeners. One down the middle long ways and two across.

When the cement has set to the point that finger pressure will just dent it,
go over it with a smooth, stiff steel trowel or spatula to make the surface
as dense as possible. Cover with a wet towel and let it sit for several
days. Keep the towen wet. Concrete reaches about 75% of its maximum
strength in about 7 days.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

wrote in message
oups.com...
I am more concerned with the design of the hull. This is a project for
my High School Engineering class, and our teacher wants us to use only
cement to get our craft to float.

How is the teacher testing the resulting shape? Is he/she using lead shot,
pea gravel, water. Is the teacher really looking for a boat/barge or the
theoretical practical solution? Lead shot in the bottom of a hemisphere
would be stable enough for a test and give you the least amount of surface
area.
Clark
"surfnturf" wrote in message
news:MIfee.1223692$6l.94600@pd7tw2no...
There certainly are lots of cement barges plying the costal rivers of
China.
Staight sides and flat botton, but probably for ease of construction and
load handling.

Might want to play with the math a little to get a fix on the shape that
encloses the greatest volume with the least surface area. Hmmm. Sounds a
lot
like half a sphere. Could cast it inside a basketball...

surfnturf


"No Spam" wrote in message
news:UTeee.7459$Rl6.7151@trndny08...

I think I would model it after river barges. very flat bottom, straight
sides and rounded up at both ends. Rectangle shape. It is used to haul
tons of coal around here every day. It is also a very simple shape to
produce. Also agree with everyone else that you need a mesh inside to
keep it all together.

Terry Spragg ) writes:
wrote:

we can use some sort of mesh or something to get the cement to hold a
shape, but it cannot be wood, or something else that would provide
buoyancy that way.


Dig a hole in the ground, line it with plastic, drive in some pins
to position rebar or position chainlink fencing for reinforcement,
plaster or even spray on concrete. Make it into a basement for a
floating house with several compartments, wait for spring floods to
launch.

It's also been done upside down. Pile up some wet sand and sculpt the boat
you want, cover that with burlap or something (I forget the details,
plaster over smoothly with wet cement mixed with beach sand (mortar),
cover with plastic sheeting (you want to keep the water in while the
cement cures), and when it cures turn turn it over and drag it down to the
water. I read aqbout this being done by someone who could not transport a
boat to a waterside vacation spot. The cement boat was left behind after
the vacation for the use of local residents. Claimed it was a success.
Note that cement has to remain moist to cure. If it dries out before it
cures it will crumble into pieces.

Piling up the sand might be better than digging down in wet locations
where a hole would fill with water. Just a thought.

--
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William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
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A highly regarded book on this topic is:

Ferro-cement

by Bingham.

HTH,

Courtney


On Fri, 26 Aug 2005 10:19:55 -0300, Terry Spragg wrote:

wrote:

we can use some sort of mesh or something to get the cement to hold a
shape, but it cannot be wood, or something else that would provide
buoyancy that way.


Dig a hole in the ground, line it with plastic, drive in some pins
to position rebar or position chainlink fencing for reinforcement,
plaster or even spray on concrete. Make it into a basement for a
floating house with several compartments, wait for spring floods to
launch.

Or did you want a speed boat?

Terry K