-I am pretty sure that tapering the mast makes it less likely to
break as it takes some of the shock out of the system and reduces
weight aloft. IMHO I think your mast if strong enough will be stiff
enough knowing the characteristics of Kiri. The only thing is the
extra weight and fatness. You are getting out there now with what you
have rather weighting for perfection. This represents a lot of extra
miles covered on the water which is what it is about.
Robert
-- In harryproa@yahoogroups.com.au, Doug Haines <doha720@y...> wrote:
>
> g;dAY,
>
> hI, i KIND OF STARTED THIS TOPIC on masts, and was just wanting
to say that tapering the end in at the top means using mirrored
shapes of the moulds (this is for he strip planked kiri and glass -
same as the hulls, and my beams), and so you need to turn all the
moulds around and hence introduce a probable error in the two halves
for when joining them together. You can compare this withthe hulls
moulds which are symetric fore and aft so you use the same mould for
each side you strip plank.
> Just might suggest not tapering the mast, for those taking the
cheapest option like myself. (Snobby Stuck up Carbon Users!)
>
> I'd like some feedback on how important stiffness of mast is to
improving sailing speed?
> Anyway back to the mast making.
>
> Doug
>
> Robert <cateran1949@y...> wrote:
> -Thanks Mike,
> I didn't realise that carbon had greater stetch before breaking
than
> glass.
> My thought on the creaking and cracking concur with yours that it
is
> probably the resin not being able to stretch enoughand some
breaking
> of the fibre resin bond. I also think that the cross fibresresin
> attachment needed to keep the compression side from buckling may
also
> crack. The concern to me is that the cracing on the ww side weakens
> the side for subsequent compression when the load changes. The
99.9%
> stability is nice to read.
> Robert -- In harryproa@yahoogroups.com.au, Mike Crawford
> <jmichael@g...> wrote:
> >
> >
> > After much research, I agree with both Peter and Rob.
> >
> > In summary: epoxy cracking likely occurs in first tension on
the
> > leading edge, while structural failure of the mast likely occurs
in
> > compression on the trailing edge. The cracking sound will
probably
> be
> > more of an issue for carbon and less of an issue for
kiri/glass.
> Also,
> > it appears that Rob's cold vacuum process for creating spars is
> > superior to the heated autoclave process, and carbon and kevlar
> > laminates are better than aluminum in terms of long-term fatigue.
> >
> > The rest of this long post contains some of the links and
> > explanation. It's not definitive, but at least it has some real
> data.
> >
> > ---
> >
> > EPOXY PROPERTIES
> >
> > I originally made two faulty assumptions: a) epoxy stretches
> more
> > than it actually does, and b) epoxy is isotropic, i.e., it has
the
> same
> > modulus in both compression and tension. The first assumption
> stemmed
> > from the fact that the flexible epoxies used in some repair work
> are
> > different from the stiff epoxies used to create masts. The
second
> > assumption came from some research refers to epoxies as being
> > quasi-isotropic, which I misinterpreted.
> >
> > Thanks to Peter for pointing out that epoxy has different
modulii
> for
> > tension and compression. Unfortunately it took me over half a
day
> to
> > get actual numbers to verify this.
> >
> > As far as stretch goes:
> >
> > http://www.tech.plym.ac.uk/sme/MATS324/MATS324A5%20CFI.htm
> >
> > Epoxy only elongates to 2% before cracking, while carbon
fiber
> can
> > elongate up to 10% before failure, and E-glass to 3.37%. As the
> leading
> > edge of a mast stretches, the epoxy will crack before carbon
fibers
> or
> > E-glass fibers will break.
> >
> > As far as modulus goes:
> >
> > http://www.rpi.edu/locker/38/001238/pdfs/load.pdf
> >
> > http://www.google.com/search?
> q=cache::www.rpi.edu/locker/38/001238/pdfs/load.pdf
> > (same as above, but html version)
> >
> > Epoxy alone has a modulus that is 17% greater in compression
than
> in
> > tension, and an epoxy/carbon composite has a modulus that is 21%
> greater
> > in compression than in tension. Both epoxy and epoxy/carbon
> composite
> > will stretch more under a given force in tension than they will
> shrink
> > under the same force in compression.
> >
> > ---
> >
> > MAST CRACKING
> >
> > Scenario A: flexible unstayed carbon mast
> >
> > If the mast is designed to be flexible, the smaller tension
> modulus
> > means that the windward side of the mast will stretch more in
> tension
> > than the leeward side will shrink in compression, and epoxy's
> earlier
> > failure due to strain means that the stretching is going to crack
> the
> > epoxy while leaving the carbon fibers intact. These cracks will
> weaken
> > the mast, but won't themselves represent a structural failure
> because
> > the undamaged carbon is still very strong.
> >
> > Scenario B: stiff unstayed carbon mast
> >
> > If the mast is stiff enough to keep the epoxy from elongating
> past its
> > strain limit, cracks won't occur in tension on that windward
edge.
> > Instead, cracks will develop from compression in the leeward edge
> as the
> > matrix starts to buckle. This is not necessarily better than the
> > flexible mast, just different.
> >
> > Scenario C: kiri/glass mast
> >
> > Because of wood's inherent flexibility, and the lower modulus
of
> > fiberglass when compared to carbon, the cracking is likely in the
> epoxy
> > on the windward edge. I don't have a modulus or strain data for
> kiri to
> > test this.
> >
> > ---
> >
> > MAST FAILURE
> >
> > When a failure does occur, it will likely happen on the
leeward
> edge
> > under compression. This is because the fibers under tension
> require no
> > support, and therefore don't put buckling stress on the matrix,
> while
> > the fibers under compression will eventually buckle once the
epoxy
> fails
> > to keep them in column. Worded differently, the compressed side
is
> > stiffer than the stretched side, but ultimately more susceptible
to
> failure.
> >
> > Scenario A: flexible unstayed carbon mast
> >
> > This mast will provide warning before failure, with the leading
> edge
> > cracking before the trailing edge buckles. That's definitely a
> plus.
> > However, the cracks will weaken the mast over time The more
cracks
> > there are in the epoxy matrix, the less it will be able to keep
the
> > fibers from buckling, and the more likely it will fail in
> compression.
> > Moral of the story: avoid stresses that cause the cracking sound.
> >
> > Scenario B: stiff unstayed carbon mast
> >
> > For a stiff carbon mast, this means that there won't be the
> benefit of
> > hearing the micro-cracks in the leading edge as the mast gets
> stressed.
> > That's a bummer if the mast has not been designed to be strong
> enough to
> > handle the dynamic loads involved in a huge gust capsizing the
> boat. If
> > the mast is strong enough, the issue then becomes making the boat
> strong
> > enough to handle the stress, while also surviving the knockdown.
> Many
> > folks would rather have the mast fail.
> >
> > Scenario C: kiri/glass mast
> >
> > Failure will likely be in compression because wood does better
in
> > tension than compression, and a hollow mast will eventually
buckle
> in
> > compression when subjected to too much force. Fortunately, the
> cracking
> > should be less of an issue with the kiri/glass mast. First, the
> kiri
> > itself is going to provide more resistance to compression than
the
> > glass/epoxy skin. Second, even if the epoxy is cracked, the
glass
> will
> > still hold tension, and will still help prevent the kiri from
> buckling.
> >
> > ---
> >
> > VACUUM-BAGGING VERSUS AUTOCLAVE
> >
> > http://www.gmtcomposites.com/the_autoclave_myth.htm
> >
> > Autoclaved prepreg masts are stronger and stiffer in tension
and
> > compression, while vacuum bagged masts are better in shear. Six
on
> one
> > side, a half-dozen on the other. However, vacuum-bagged masts
can
> be
> > made in one long piece, regardless of length. Autoclaved masts,
on
> the
> > other hand, must be spliced together from sections that fit in
the
> > autoclave. For a small mast, this doesn't matter. For a large
> mast,
> > this means joints between sections, and that's less desirable
than
> a
> > single piece.
> >
> > ---
> >
> > FATIGUE
> >
> > http://www.tech.plym.ac.uk/sme/MATS324/MATS324A5%20CFI.htm
> >
> > "Under a static load of 50% ultimate stress, the probability of
> > survival for carbon/epoxy, Kevlar/epoxy and glass/epoxy over a 30
> year
> > period are 99.99%, 99.8% and 22% respectively. Under a load of
40%
> > ultimate stress, the survival probability for glass/epoxy is 97%"
> >
> > http://www.cstcomposites.com/505_carbon_spar.htm
> >
> > "Fatigue resistance orders of magnitude better than
> Aluminium .Life
> > Span - pretty well indefinite with normal sailing loads apart
from
> > normal wear and tear."
> >
> > Not that anyone needed a reason to like carbon. I've just seen
> fans
> > of aluminum insulting carbon's ability to resist fatigue. I
> suppose
> > early designs could have had problems, but that would seem to be
a
> > design or manufacturing issue, not a materials issue.
> >
> > - Mike
> >
> >
> >
> >
> > Peter Southwood wrote:
> >
> > > Hi Rob,
> > > I dont see why the resin should crack because the carbon is
> stiffer.
> > > If the resin cracks it is because it is stressed beyond its
> maximum
> > > strength. The stiffer the fibres, the less likely the resin is
to
> > > reach failure strain before the fibres. More likely the resin
> cracks
> > > because it is too stiff for the fibres and does not have a
> matching
> > > strain at failure.
> > > Cheers,
> > > Peter
> > >
> > > ----- Original Message -----
> > > From: Rob Denney <mailto:proa@i...>
> > > To: harryproa@yahoogroups.com.au
> > > <mailto:harryproa@yahoogroups.com.au>
> > > Sent: Friday, November 03, 2006 7:23 AM
> > > Subject: Re: [harryproa] Re: masts
> > >
> > > G'day,
> > > Yes, but the stiffer it is, the more cracking there will
be.
> My
> > > understanding of this is that the noise is the resin
cracking
> as
> > > the carbon is so much stiffer. With glass and kiri, there
> may be
> > > less cracking, or it may just happen at a higher load.
> > > Regardless, I think you will get plenty of warning. Maybe
> test a
> > > piece of kiri and glass by bending it until it starts to
> crack,
> > > then see how much more it will take before it is visibly
> damaged.
> > > This may give you some idea of how far you can go past the
> > > cracking stage.
> > >
> > > regards,
> > >
> > > Rob
> > >
> > > ----- Original Message -----
> > > From: Doug Haines <mailto:doha720@y...>
> > > To: harryproa@yahoogroups.com.au
> > > <mailto:harryproa@yahoogroups.com.au>
> > > Sent: Friday, November 03, 2006 1:13 PM
> > > Subject: Re: [harryproa] Re: masts
> > >
> > > Rob,
> > >
> > > Is composite glass/kiri?
> > >
> > > Doug
> > >
> > >
> > >
> > > Rob Denney <proa@i... <mailto:proa@i...>> wrote:
> > >
> > > If it is composite, you will hear a lot of creaking
> and
> > > cracking before it breaks. I would work on one of
> them
> > > doing the lifting as in a capsize you will probably
> have
> > > dumped one of them.
> > >
> > > regards,
> > >
> > > Rob
> > >
> > > ----- Original Message -----
> > > From: Doug Haines <mailto:doha720@y...>
> > > To: harryproa@yahoogroups.com.au
> > > <mailto:harryproa@yahoogroups.com.au>
> > > Sent: Thursday, November 02, 2006 12:13 PM
> > > Subject: Re: [harryproa] Re: masts
> > >
> > > Robert,
> > >
> > > I'd like to sense a failure ahead of the crack,
> split
> > > whatever, so as to salvage the mast and simply
add
> > > more glass around the outside. But that would
be a
> > > fairly satisfactory level of strength if they -
> cause
> > > there are two of them - raise the hull.
> > >
> > > Doug
> > >
> > > Robert <cateran1949@y...
> > > <mailto:cateran1949@y...>> wrote:
> > >
> > > Easy enough to check if the masts are strong
> > > enough. Load them up by
> > > trying to lift the ww hull with a 100kg
weight
> > > sitting on it.
> > > I was looking at the characteristics of
> quality
> > > bamboo section and it
> > > looks considerable better than glass weight
> for
> > > weight with 4GPa
> > > youngs modulus and a breaking strain of
> 30kg/mm 2.
> > > It may be worth
> > > considering for cheap masts. I am
considering
> it
> > > myself for skinning
> > > cores in areas where exra stiffness is
wanted
> > > without the expense of
> > > carbon. Hope carbon becomes more easily
> available
> > > and cheaper as it
> > > is by far the best material.
> > > Robert
> > > -- In harryproa@yahoogroups.com.au, "Robert"
> > > <cateran1949@y...> wrote:
> > > >
> > > > --- In harryproa@yahoogroups.com.au, Doug
> Haines
> > > <doha720@y...>
> > > wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > Just meant swinging around on the
water,
> > > like anchored in the
> > > sea
> > > > breeze comes in 20knots.
> > > > >
> > > > > I was wondering about general ideas
> about
> > > swinging around
> > > coming
> > > > from experienced multihullers out there.
> Like
> > > when you anchor a
> > > > bigger boat out further where the wind
is.
> What
> > > about two anchors
> > > 30
> > > > degrees apart?
> > > > >
> > > > > Mast is same as boat - kiri strip and
> glass.
> > > > > I've tapered the tops to half
> dimensions.
> > > There is a round pole
> > > > up a metre and a half into the mast that
> slots
> > > in the hull. I hope
> > > it
> > > > is all not going to break.
> > > > > Obviously it is heavy but is cheaper.
> > > > >
> > > > > Doug
> > > > >
> > > > >
> > > > >
> > > > > Myriam & Youri <wangka@s...> wrote:
> > > > >
> > > > >
> > > > > v\:* {behavior:url(#default#VML);}
> o\:*
> > > {behavior:url
> > > > (#default#VML);} w\:*
> > > {behavior:url(#default#VML);} .shape
> > > > {behavior:url(#default#VML);}
> > > st1\:*{behavior:url
> > > > (#default#ieooui) } Dear
> Doug,
> > > > >
> > > > >
> > > > > Dear Wangkas,
> > > > >
> > > > >
> > > > >
> > > > > Nice pictures and all, but where is
a
> > > finished sailing boat?
> > > > > We know it takes a long
> time,
> > > but sometimes we have
> > > > other worries on our minds ... like
carbon
> spars
> > > for classical yachts
> > > > where we have to sort out two boats,
masts,
> > > booms, sprits, poles
> > > > etc, we have to make molds and plugs for
> > > rudders, keels and bulbs,
> > > ...
> > > > for the carbon parts we are achieving and
> > > testing a construction
> > > > method VAPM (vacuum assisted pressure
> molding
> > > that gives us
> > > autoclave
> > > > quality laminates (not only on the voids
> ratio
> > > but also on the
> > > > compression side) in our pressure molds(
> > > compression +-5 Bars)
> > > which
> > > > can produce one piece parts, which is not
> > > possible by standard
> > > > autoclave procedures. We are also
currently
> > > testing a method for
> > > > direct CNC mold cutting for parts
> construction ...
> > > > >
> > > > > Also, what do you hope to acheive
with
> > > around beam?
> > > > >
> > > > > They are not only rounded in
length
> but
> > > also elliptical in
> > > > section and will be constructed VAPM...
less
> > > windage, better stress
> > > > distribution, less wave interference ...
> > > > >
> > > > > Thanks again for your mast section,
> it is
> > > coming together.
> > > > > We are glad, how are you
> going
> > > to construct it ? ...
> > > > >
> > > > > The boat really swings around at the
> > > moment without masts up
> > > > and I wonder if it can be helped? More a
> > > question for the cruising
> > > > boaters - do you plan doing cruising
> Elementarries?
> > > > > What do you mean with
> swinging
> > > around ? I suspect
> > > we
> > > > will but that depends on the interest
> shown ...
> > > for the moment we
> > > have
> > > > some asks for quotes from France,
> Switzerland
> > > and Germany ...
> > > > >
> > > > >
> > > > > Best regards,
> > > > >
> > > > >
> > > > > Myriam & Youri
> > > > > Wangka bvba
> > > > > Belgium
> > > > >
> > > > > e-mail. info@w...
> > > > > web. www.wangkaboats.eu
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > yaendenboom <wangka@s...> wrote:
> > > > >
> > > > > Dear people,
> > > > >
> > > > > Our site has been updated.
> > > > > We kindly invite you to have a look at:
> > > > > www.wangkaboats.eu
> > > > >
> > > > > Suggestions and criticism is welcome at:
> > > > > info@w...
> > > > >
> > > > > Thank you very much,
> > > > >
> > > > > Myriam & Youri
> > > > > Wangka bvba
> > > > > Belgium
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > Send instant messages to your online
> friends
> > > > http://uk.messenger.yahoo.com
> > > <http://uk.messenger.yahoo.com/>
> > > > >
> > > > >
> > > > >
> > > > > Send instant messages to your online
> friends
> > > > http://uk.messenger.yahoo.com
> > > <http://uk.messenger.yahoo.com/>
> > > > >
> > > >
> > >
> > >
> > >
> > >
> > > Send instant messages to your online friends
> > > http://uk.messenger.yahoo.com
> > > ------------------------------------------------
--
> ----------------------
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> > > Checked by AVG Free Edition.
> > > Version: 7.1.385 / Virus Database:
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> > > Release Date: 8/23/2006
> > >
> > >
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