|Subject: Re: [harryproa] Re: Schooner v. Unarig|
|Date: 12/12/2006, 5:34 AM|
Can you help us with this detail:
. We use 20 of them (carbon tows) to spread the load over about 600mm
all round the mast. To further spread the load there is a bulkhead under
the mast and a stringer along the keel and under the deck.
Our plans are missing these details.
How is this done on Visionarry? Can you send us details about mast
bearings and mast support.
Is there carbon on the lw hull around the mast?
> Difficult to know where the rig will fail. The lower part is
comparatively massive to provide enough stiffness. I suspect just above
the hounds, but it would vary a lot depending on the rig at the time.
> Finite element analysis is a good tool, but only if you are looking to
minimise everything. On the cruisers we use large safety factors, and
overbuild critical areas so standard engineering is fine.
> My experience of carbon is that it is pretty good on impact. I have
dropped carbon masts off roof racks under circumstances that would have
dented alloy. The carbon masts are still standing. My experience is
supported by golf club, racquet sports and F1 cars bouncing over kerbs,
all of which see severe impacts with surprisingly little damage. Where
carbon is at a disadvantage is that impact damage is not visible. It is
very rare to hear of a mast failing due to the carbon. It is almost
always a rigging failure, or can be traced to a former incident which
damaged the mast. I know of no unstayed masts which have failed. If
anyone does, please let me know the details.
> Carbon is particularly good for unstayed masts as along with low
weight and high stiffness, it has the best fatigue properties of any of
the common building materials.
> ----- Original Message -----
> From: jjtctaylor
> To: harryproa@yahoogrou
> Sent: Sunday, December 10, 2006 5:38 PM
> Subject: [harryproa] Re: Schooner v. Unarig
> 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 harryproa@yahoogrou
> > 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.
> > >
> > > _._,___
> > >
> > >
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