Horses for courses. It is hard to beat bamboo for ability to take
loads and torque from all directions but if the bamboo was
constrained with the load more in one direction I would imagine it
would end up more oval.
If there is no problem with torque go for an I beam. My idea for a
folding beam is based on an I beam, allowing easier load transfer
when partly folded, with judicious addition of fairing to provide
resistance to torque and fore and aft bending moment. It is tempting
to just buy some of those composite beams used in the building
industry as a start
For simplicity in building and reasonably close to optimum I would
go for a ring framed wooden box section reinforced on the corners
with carbon tow. This way the web can also act as a flange.
Fibreglass in the same circumstances would be less useful as it
stretches too much and the timber goes past its limit long before the
fibreglass takes up the strain. There may have to be some cloth
reinforcement around the beam to prevent the carbon tow from
delaminating from the timber.

I have been closely observing the Harry construction and I am most
impressed with the engineering. It seems to be based on years of sea
time and knowing what breaks, and mathematical and material analysis
on how to best achieve the strength required with building techniques
within the ability and cost of the low volume builder. I certainly
wouldn't stray from the specs. This is what you're paying the money
for.


--- In harryproa@..., "Tony Richardson"
<atrichardson@b...> wrote:
>
> ----- Original Message -----
> You wrote
> - You have to make a box section, nothing else is remotely
> comparable.
>
> I dissagree
> I'm no engineer but I do have a tri with round beams
> Rob and I built them in a female mould mostly of uni's
> It flies two hulls and has no seastays/wires etc
> They have a degree of flex in them though
> The beams weigh 5kg each bare.
> The boat is only 16ft but it is 15ft wide
> Rgs
> Tony