Mike,
We are completely in agreement. I was trying to refer to the
compressive forces imposed on the mast by the stays and assuming the
forces would be at maximum when the boat falls off a wave.
You are way ahead of me in design skill and experience. I am an
actuary and know nothing about design or engineering. I just looked
up the beam deflection equation a few days ago. I can understand the
arithmetic, but everything else is entirely new for me.
Best regards
Herb
--- In harryproa@yahoogrou
>
> Herb,
>
> I don't quite get everything you're saying, but that's probably due to
> my lack of design experience. Houses, garages, and bridges were my
> forte when I was a civil engineer, and none of the stresses encountered
> would be like those on multihulls.
>
> Regardless, it looks like we're in general agreement. While the mast
> still has to be strong, particularly in bending moment, it won't have to
> deal with some pretty fierce loads that stays would put on it. It's
> particularly nice not to have to deal with compressive forces as the
> mast slowly bends out of column due to wind loading. Let it bend! That
> eliminates the need for diamond stays, which lightens the load, reduces
> windage, eliminates additional compression and point loads, and so
forth.
>
> As with Rob, I've not yet heard of a carbon mast failing on its own.
> Then again, I'm the guy who came up with the wrong elongation at failure
> for carbon after finding some odd research, so my chiming in on this is
> of questionable value. Thanks again to Myriam and Youri for sending the
> link to http://www.matweb.
> all sorts of combinations of carbon, fiber, strain, failure, and so
> forth, but not knowing about matweb.com, and not using the
> obvious-in-hindsigh
> much of the data was contained in pay-only research papers that it was
> tough going.
>
> It would be useful if we could find out the exact specs used on the
> freestanding carbon masts at Wyliecat ( http://www.wyliecat
> because they've had the chance to test them for a while. The Wyliecat
> spars would be more equivalent to those used on the harryproas than the
> stayed rotating wingmasts one normally sees.
>
> - Mike
>
>
>
> Herb Desson wrote:
> >
> > Mike,
> >
> > Sorry I wasn't clear. What I meant was that although the motion of
> > the boat will be transferred to the masts, the mass affecting the
> > masts will be only that of the mast and sails themselves, instead of
> > the entire mass of the boat being transferred through the stays. So
> > the total energy the unstayed masts have to deal with will be a tiny
> > fraction of the stayed masts.
> >
> > A boat with a stayed mast is effectively a large complicated spring
> > system in which all the mass of the boat is eventually transferred to
> > the mast. But for an unstayed mast there is no spring system that is
> > tied to the mast. Still plenty of springs, but none (or very few) of
> > them wind up being transferred to the mast.
> >
> > Best regards
> > Herb
> >
> > --- In harryproa@yahoogrou
> > <mailto:harryproa%
> > wrote:
> > >
> > >
> > > I believe that boat motion will be transferred to the mast in either
> > > case, whether it is stayed or freestanding. After all, if the boat
> > > heels 20 degrees due to wave action, the mast is going to have
to heel
> > > with it.
> > >
> > > 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. This will definitely simplify design. But
issue
> > > of moving the mast when the boat moves still remains.
> > >
> > > Fortunately, forces from the ocean on the mast are likely to be far
> > > less than wind forces, so designing for the sail area is still
probably
> > > a safe bet. Provided, of course, there's a pretty solid margin of
> > > safety. Just as an rock climber can put several g's of force on a
> > > climbing rope with even a 1m fall, the dynamic forces which cause a
> > > capsize can still be several times the righting moment.
> > >
> > > - Mike
> > >
> > >
> > >
> > > Herb Desson wrote:
> > > >
> > > > JT,
> > > >
> > > > That is a very interesting and long thread. I have only read the
> > > > first two pages, but one thing strikes me - that nearly all of the
> > > > problems in design relate to what happens to the stays when a
big bump
> > > > happens because the entire momentum of the boat is transmitted
through
> > > > the stays via the mast.
> > > >
> > > > On a free standing mast it seems that the only issues are the
righting
> > > > moment and fatigue. Once the boat goes over there is very
little load
> > > > and much bigger problems than a broken mast. But you can never
have a
> > > > problem with the momentum of the boat being transmitted
through the
> > > > stays to the mast and deck. So the problem is much simpler.
> > > >
> > > > I think we can design for righting moment only (plus fatigue and
> > > > construction error) and be safe enough. Any more would just create
> > > > more mass than necessary or would ever be used.
> > > >
> > > > Best regards
> > > > Herb
> > > >
> > > > --- In harryproa@yahoogrou
> > <mailto:harryproa%
> > > > <mailto:harryproa%
<jtaylor412@
> > > > wrote:
> > > > >
> > > > > You will have to choose your fudge factors for sail force.
It isn't
> > > > > just load to capsize..... I am not an expert but a really long
> > > > > discussion can be found at:
> > > > >
> > > > > http://boatdesign.
> > <http://boatdesign.
> > > > <http://boatdesign.
> > <http://boatdesign.
> > > > >
> > > > > Whole books have been written on rig planned loads. Even without
> > > > > stays..... forces are dynamic so a whole bunch of engineers and
> > > > > experts cannot yet agree on how much engineered strength
(loads)is
> > > > > enough. The sea is dynamic, wind is dynamic and boat motion as
> > > > > well. FEA may tell you what may fail first.....but not the
> > > > > conditions that caused it. So have to make a bunch of
> > > > > assumptions,
too many
> > > > > variables. Thus make your planned limit then add something
for for
> > > > > the unknown.
> > > > >
> > > > > NO matter what... impractical to design for all
possibilities, so if
> > > > > designed to function adequately well it be lost under some
extreme.
> > > > > Choose your limit, you won't be right or wrong.
> > > > >
> > > > > JT
> > > > >
> > > > >
> > > > > --- In harryproa@yahoogrou
> > <mailto:harryproa%
> > > > <mailto:harryproa%
<squirebug@>
> > > > > wrote:
> > > > > >
> > > > > > Ah, I take your point. So the relative force on the mast
due to
> > > > > sail
> > > > > > size is largely irrelevant.
> > > > > >
> > > > > > So we will gain strength due to the shorter masts, but
weight will
> > > > > be
> > > > > > governed by breaking strength. Need to do some more research.
> > > > > >
> > > > > > Thanks for straightening me out.
> > > > > >
> > > > > > Best regards
> > > > > > Herb
> > > > > >
> > > > > > --- In harryproa@yahoogrou
> > <mailto:harryproa%
> > > > <mailto:harryproa%
wrote:
> > > > > > >
> > > > > > >
> > > > > > > ----- Original Message -----
> > > > > > > From: Herb Desson
> > > > > > > To: harryproa@yahoogrou
> > <mailto:harryproa%
> > > > <mailto:harryproa%
> > > > > > > Sent: Friday, December 01, 2006 5:27 PM
> > > > > > > Subject: [harryproa] Re: Schooner v. Unarig
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > I am not quite sure what to make of the smaller sail
area, but
> > > > > I think
> > > > > > > it is clear that in any given weather there will be less
force
> > > > > on each
> > > > > > > mast for the schooner than for the single mast of the sloop.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > Agreed, but the design load is still that force required to
> > > > > > capsize the boat, so they have to be as strong as the single
> > > > > mast.
> > > > > > The same applies to the hull reinforcing. Supporting each
mast at
> > > > > the
> > > > > > end of the beam is very easy. However, if only one sail is
doing
> > > > > the
> > > > > > work, the hull has to be strong enough to transmit this load
> > to the
> > > > > > other beam, so ends up the same as if the mast was in the
middle.
> > > > > > >
> > > > > > > I look forward to seing the results of your calculations. I
> > > > > know FEA
> > > > > > > costs money, but would it be possible to include an
analysis of
> > > > > > > exactly the same sail shape to get comparability? I am
not sure
> > > > > how
> > > > > > > comparable a jibless schooner is to a balestron sloop from a
> > > > > weight
> > > > > > > point of view. My first thought is that it wouldn't make
much
> > > > > > > difference, but clearly my first thoughts are not very
reliable
> > > > > in
> > > > > > > these matters.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > You ain't kidding about the cost of FEA! I can't afford
to get
> > > > > > into sail shape anaysis. We engineer the mast based on the
> > > > > scenarios
> > > > > > it sees. The ballestron rig and the schooner would be
pretty close
> > > > > to
> > > > > > the same weight.
> > > > > > >
> > > > > > > Best regards
> > > > > > > Herb
> > > > > > >
> > > > > > >
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> > > > > > >
> > > > > > > Internal Virus Database is out-of-date.
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