Rob,

Responses in-line

On Thu, May 19, 2011 at 9:21 PM, Rob Denney <harryproa@gmail.com> wrote:

 

Hopefully Rick will answer the performance question.

The box spar is a good idea, can be made to taper in both section and laminate very easily.  

Yes, I can see that tapering the tube is easy, but that makes the leading and trailing edge construction harder. 

The leading edge over a tube is hard work due to the flat sides.  Much easier to make it from a flat panel and bend it to an elliptical shape, then add glass to the inside or outside.   Experiment with the flat panel till you get a laminate that bends naturally into an ellipse.  should be able to get close with 3 layers of 200 gsm cloth of varying widths.

 

It is the bending to an elliptical shape, especially a tapered one, that worries me the most. It would seem that you would need some sort of form to make a uniform curve over a 35-40' length, which is why I thought of the semicircle. I also wasn't sure that the leading edge really needed the rigidity of cored construction. When I imagine it in my mind, the bending loads are taken by the spar and the trailing edge has the sail attachment loads, but the leading edge seems like it would be fairly unloaded and could be made uncored, and maybe even without carbon fiber. 

The trailing edge can be panels with glass on the inside only.  Use a spacer to spread them a little in the middle to induce some curvature, then glass the

I can see this. I was trying to simplify as much as possible, but this could be doable. Each panel can be built seperately, then the spar and spacer can be attached to one and then the top panel can be attached to the spar and after it has cured, it epoxy can coat the spacer and the 2 panels bent together to trap the spacer and join the trailing edge. It wouldn't be that much more work than just leaving the side panels flat.

 

outside.  A bit of bog to make the sides of the box spar rounded and a track and you will be very close to optimal. 

Reinforce the mast at the deck bearing and boom with either an internal bulkhead or an external wrapping.

rob

On Fri, May 20, 2011 at 9:39 AM, Gardner Pomper <gardner@networknow.org> wrote:

 

Hi,

I am still a bit hung up on how much of the expense of building a boat
is tied up in the masts. I know that Rob is working on techniques, but
I haven't see him publish anything and I expect that he is still
relying on the builder not being a complete moron and fumblefingers. I
can't afford to make those kind of assumptions <grin>.

Anyway, I have uploaded a really simple idea for building a wing mast
(crude_wingmast.pdf in Files). The idea is to make the central "tube"
just like the crossbeams, out of a flat sheet, folded into a square.
The leading edge could be infused over a PVC septic pipe, and the
trailing edge of the wing would just be 2 more flat panels.

There are several really obvious problems with this, such as a
semicircular leading edge instead of a elliptical edge. Also, the
trailing edge is flat, instead of elliptical. I know this isn't
optimal, but I don't have any way to determining how much it hurts
performance. Is this something that Xfoil can do, for those of you who
have it? It would be great if we could get some numbers out that would
say how much less force the sail would produce.

Another severely non-optimal factor is that the mast would not taper
towards the top. I know it will increase weight aloft, but that seems
of little significance in a multihull which sails basically flat. It
might need to reef earlier, but I could live with that, if the
difference is minimal.

The common thread with all these suggestions is fairly obvious. I know
that there are fields where alot of effort is put into optimization,
but with marginal benefit in the real world. I know that is true with
writing software, and I am hoping that there are people here who are
knowledgeable enough to not just figure out the difference, but who
can also explain how much difference would be apparent in the real
world.

I think that the harryproa concept has hit huge performance benefits
from the basic proa concept, reducing weight and making the hulls so
slim. I wonder how much more optimization we need.

- Gardner