<<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