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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