I am considering to cast myself a planing boat out of marine grade concrete - I know they use it for sailboats with displacement hulls, but would it work for a light boat, too?

On Fri, 3 Dec 2010 13:13:53 +0000, terryjohnson
wrote:


I am considering to cast myself a planing boat out of marine grade
concrete - I know they use it for sailboats with displacement hulls, but
would it work for a light boat, too?

Very doubtful. Even on displacement sailboats ferro-cement ends up
being too heavy unless the boat is well into the 40 to 50 foot range.
There are other issues as well, not the least of which is the
inability to get insurance.

On Fri, 3 Dec 2010 13:13:53 +0000, terryjohnson
wrote:


I am considering to cast myself a planing boat out of marine grade
concrete - I know they use it for sailboats with displacement hulls, but
would it work for a light boat, too?


Err... the correct term to refer to a
"concrete boat" is "ferro-cement" which comes from the way that they
are built., ferro meaning steel or iron.

A ferro boat is built by first framing the hull with steel reinforcing
bar, then covering this form with steel mesh and lastly "stuccoing
over this "armature" with concrete applied largely with a trowel.

You idea of casting a boat, disregarding the weight problem, is that
concrete is hell for strong in compression but not really worth a damn
in tensile or bending strength.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

Terry,
In addition to the other comments, there is no such thing as marine concrete. The last time I worked on a concrete hull (1970s),
it was simply Portland #5 with a very fine quartz sand mix. These hulls are very difficult to build without flaws (air pockets &
cracks). Once the steel structure is completed, it takes a large, well coordinated crew to execute the application of the
concrete. We used a concrete pump, several vibrators and two lathers with trowels inside and another two lathers on the outside.
All the concrete must be applied in a single effort. Curing must be delayed until all the concrete is applied, otherwise bonding
issues and cracks will occur. It is a logistic nightmare. Personally, I have never seen a hull without flaws. I think it is
impossible. Once all the concrete has been applied the hull must be totally covered in canvas and soaked with a hose every few
hours both inside and out for thirty days. Assuming this has been done correctly, the hull will still be full of small microscopic
cracks. The hull must be then sanded smooth and epoxied to both fill the cracks and create a surface for paint.

The result is a very expensive, heavy, low performance hull that if damaged can never be adequately repaired. This method of
construction is viable for concrete, low maintenance, disposable open barges and nothing more.
Steve

"terryjohnson" wrote in message ...

I am considering to cast myself a planing boat out of marine grade
concrete - I know they use it for sailboats with displacement hulls, but
would it work for a light boat, too?




--
terryjohnson