Subject: [harryproa] Re: Schooner v. Unarig
From: "jjtctaylor" <>
Date: 12/10/2006, 4:38 AM

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.


--- In, Mike Crawford <jmichael@...>
> Chris,
> You're entirely right. Those loads will definitely be transmitted
> through the boat, and the structure will have to be designed to
> 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
> the hulls to pitch independently, but I personally have doubts about
> trusting such a joint long-term. Besides, a single aka with
> 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
> 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
> load in the center where the mast is stepped, large point loads on
> 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
> mast snaps back in the opposite direction due to wind/wave action
> twisting in the structure.
> That's a lot of loading to handle while attempting to keep the
> from twisting lengthwise. If there were four symmetric stays,
> 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
> to swept shrouds and a forestay, there's a lot of stress induced in
> structure while flying a hull.
> While the harryproas will still have to keep themselves together
> relatively stiff as each hull hits different waves, they won't have
> 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
> > due to lack of shrouds, but the other two (torsional and point
> > 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
> > 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
> > all sorts of torsional stresses on the boat, nor point loads
> > compressive stresses on the mast.
> >
> > _._,___
> >
> >

Recent Activity
Visit Your Group
Y!7 Toolbar

Get it Free!

easy 1-click access

to your groups.

Yahoo!7 Groups

Start a group

in 3 easy steps.

Connect with others.