So you still think having the mast and sail in leeward hull would be lighter and beams requiring less strength. Compared to just a float to lee. The logic just doesn't make sense.
Todd
--- In harryproa@yahoogroups.com.au, Mike Crawford <mcrawf@...> wrote:
>
> <<Its marginal if all is rigid and designed to function taking that into
> consideration>>
>
> That simply is not true.
>
> If you can quantify the forces to demonstrate that they are marginal,
> you might be able to make a convincing point. If you can't quantify the
> forces, then you don't have enough information to say whether or not
> they are marginal.
>
> For the sake of discussion, let's do a sample calculation with rough
> numbers.
>
> Say you're on a Visionarry with 774 square feet of sail area, in a
> 20-knot wind. The Sail Wind Load calculator at sailingusa.info (
> http://www.sailingusa.info/cal_wind_load.htm ) calculates the load at
> 1300 lbs. Assuming the center of effort on the rig is 1/3 of the way up
> from the attachment to the beam, say 18 feet, that's 23,400 lb-ft of
> moment that the boat needs to resist pitchpoling. The actual force is
> several times that, because you have to design for: a) gusts, b)
> plowing the bows into a wave, and/or c) plowing the bows into a wave
> during a gust. But let's just assume 23,400 lb-ft of moment.
>
> If the rig is in the lee hull, the force is transferred directly to
> the bows through the hull, leaving the beams largely out of the
> equation. The hull takes the load. The beams do have to deal with the
> righting moment, but that's a separate calculation, one which has
> already been diagrammed, discussed, and largely agreed-upon.
>
> If the rig is in the windward hull, that 23,400 lb-ft of moment needs
> to be translated through the beams into the leeward hull so that it can
> resist that pitchpoling moment. That means torque going through each
> beam. Personally, I'd say that 23,000+ lb-ft of torsion is not a
> marginal load.
>
> If you've ever done a torsion calculation in a square box beam, you'll
> know how difficult the forces are to deal with. If you haven't, you
> might not have the background to decide what's marginal or not.
>
> That said, my training was in civil engineering, and I don't know
> enough to design boats.
>
> I'm happy for anyone to correct me with a better assessment of the
> forces at play. Not a flip "that's not significant" statement, but an
> assessment involving actual forces and numbers.
>
> - Mike
>
>
> On 11/21/2010 8:38 PM, tsstproa wrote:
> >
> >
> > Built in safety factor beam still sees less force than weight dominant
> > windward hull.
> >
> > Referring to a different force. Aw I see that too, Its marginal if all
> > is rigid and designed to function taking that into consideration, Lee
> > float skips across waters surface very little torsional load its a
> > float not a hull.
> >
> > Todd
> >
>