What I find hard to believe is that the beams on Robs boats would be any lighter than those of an atlantic prao design.
Or that the stayed rig vs the unstayed rig is in any way a weight reduction worthy of performance.
According to Arthur Edmunds.
Where as for a craft with a beam of 17' on center with a weight of 12,000lb heavy will create a bending moment of 80,500ft-lb = 966,000 in-lb or 11,139 kg-m.
Sesction moduluse (SM)= BM/S where S=29,000 psi for glass fiber (199,810kPa)
Use a FS= 2. required SM =966,000(2)/29,000=66.6 in*3
Basically using two , 8in x 8in x 0.5 walled box beams.
Whats the weight of each beam compared to robs proa?
I figure if carbon was used drop the weight by 1/3 per beam or more possibly depending on process used for laying up each beam.
Todd
--- In harryproa@yahoogroups.com.au, Mike Crawford <mcrawf@...> wrote:
>
> John,
>
>
> I'm just a fan of designing forces out of the equation, and have been
> since my engineering days in college. Thus, I like the harryproa
> downspiral design: Eliminating torsional (forces in line) and
> compression forces (unstayed mast) means less weight, which means less
> sail, which means lower forces, which means a lighter structure, which
> means less sail, and so forth.
>
> At the same time, less carbon and epoxy mean a lower cost, as does
> skipping additional structures such as crew pods.
>