5-6m righting arm and 1500kgww hull,4-5m cofe and you have 2m bury,
gives a bit over 4500kg pointloading on the bearing x3 for dynamic
loads 113500kg point loading. I am assuming the engineering is quite
capable of designing the masts strong enough, but I can see where
the boat has to be reinforced.
Robert--- In harryproa@yahoogrou
<jtaylor412@
>
> Question for Rob,.....
>
> Cause I know hew loves the epoxy.... How is the mast held in place
> and what takes the load. Looking at the design 1500lb wind load
or
> so with a 12-15 ft CE above the hull makes for a lotta torque, not
> withstanding any peak loads due to accel or decel. Top ring takes
> 5/8 of that and bottom ring takes the balance. Is there another
> material, balsa, etc that can handle high compressive forces ?
How
> does that force get distributed over the hull top/bottom.
>
> So basically where will the rig fail if overloaded and how ?
> Strength of materials may support the unusual tip over, rather
than
> an actual failure. Visionarries may have too high a CE and thus
> break the mast whereas the lower CE of Elementaries and HarryP's
get
> a dunking.
>
> Finite Element Ananlysis despite high cost could determine answers
on
> much is the mast capability. Nice about the unsupported is there
is
> a clean point load at the mast contact with hull, albeit a fairly
> sharp load point.
>
> Tougher questions is how does the carbon fail, which was a
discussion
> a while back. That still takes expertise for what is failing in
the
> laminate structure and when is limit reached. All are unanimous
that
> carbon does not fair well with shock loads, lots of high stress
cup
> racing rings falling down. Those folks may never tell the public
> why...... but has always caused wonder, since us HarryProa fans
like
> an unsupported rig type, but with a material that may not like it !
>
> Nice to have a broad discussion over over how the rig is actually
> supported and where ARE the risks.
>
> JT
>
> --- In harryproa@yahoogrou
> wrote:
> >
> > Chris,
> >
> > You're entirely right. Those loads will definitely be
transmitted
> > through the boat, and the structure will have to be designed to
> handle
> > them. Additionally, with a 9m beam, there will obviously be
torsion
> > when one hull hits a wave before the other does.
> >
> > There is a proa design out there with a single large beam that
> allows
> > the hulls to pitch independently, but I personally have doubts
about
> > trusting such a joint long-term. Besides, a single aka with
> independent
> > hulls leaves no room for a large deck with massive trampolines.
> Why get
> > a large multihull if you can't stretch out?
> >
> > The difference in the unstayed mast would be in the way the
> structure
> > is loaded. Given a catamaran or trimaran with a stayed mast,
> there's a
> > lot of stress the structure has to handle. There a large
> compressive
> > load in the center where the mast is stepped, large point loads
on
> the
> > hulls/amas at the chainplates, loads due to righting moment while
> > heeling, and also wave loads.
> >
> > Compounding the matter is the problem of keeping the structure
> > torsionally stiff enough to keep the leeward stays from getting
too
> > loose as the boat twists. This not only puts more force on the
> > forestay, it also allows a jolting point load on a chainplate
when
> the
> > mast snaps back in the opposite direction due to wind/wave
action
> and/or
> > twisting in the structure.
> >
> > That's a lot of loading to handle while attempting to keep the
> boat
> > from twisting lengthwise. If there were four symmetric stays,
> either
> > shrouds parallel with the mast step and fore- and mainstays, or
two
> > shrouds on a side, there's less torsion to deal with. But when
> compared
> > to swept shrouds and a forestay, there's a lot of stress induced
in
> the
> > structure while flying a hull.
> >
> > While the harryproas will still have to keep themselves
together
> and
> > relatively stiff as each hull hits different waves, they won't
have
> to
> > deal with the additional huge wrenching forces induced by stays
in
> > tension with a mast in compression.
> >
> > - Mike
> >
> >
> >
> > Chris Ostlind wrote:
> > >
> > > Hi Mike,
> > >
> > > I understand the part below about the compressive stress on
the
> boat
> > > due to lack of shrouds, but the other two (torsional and point
> load
> > > stress) kind of escape me with regards to a freestanding mast.
> > >
> > > Is not the mast point loaded at the mast partner location (the
> deck in
> > > most cases) once dropped into place and placed under wind load
by
> the
> > > sail(s)?
> > >
> > > Is not the moment generated through the mast focused into the
hull
> > > torsionally through the partner location as fulcrum and then,
> > > subsequently, to the mast step?
> > >
> > > Chris
> > >
> > >
> > >
> > > ----- Original Message -----
> > > From: Mike Crawford <mailto:jmichael@
> > >
> > >
> > >
> > > The nice thing about a freestanding mast is that there
won't
> be
> > > all sorts of torsional stresses on the boat, nor point
loads
> and
> > > compressive stresses on the mast.
> > >
> > > _._,___
> > >
> > >
> >
>
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe