Subject: [harryproa] Re: Schooner v. Unarig
From: "Robert" <cateran1949@yahoo.co.uk>
Date: 11/30/2006, 11:00 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

The boat is always going so fast that it is closehauled (;~)
Robert
--- In harryproa@yahoogroups.com.au, "Jim Baltaxe" <jim.baltaxe@...>
wrote:
>
> Huh?
>
> I would imagine that the precise location of the masthead would be
> irrelevant in this respect since the boom will extend much further
to
> leeward, no matter what the angle of the mast.
>
> Which one of us has missed something important here?
>
> Enjoy
>
> Jim Baltaxe
> ITS Desktop Support
> Victoria University of Wellington
> NEW ZEALAND
> (04) 463 5018 or 027 563 5018
>
> I suffer from mental incontinence.
>
> Klein bottle for rent. Inquire within.
> "If we knew what we were doing, it wouldn't be called research,
would
> it?" -- Albert Einstein
>
>
>
>
> ________________________________
>
> From: harryproa@yahoogroups.com.au
> [mailto:harryproa@yahoogroups.com.au] On Behalf Of audeojude
> Sent: Friday, 1 December 2006 1:31 a.m.
> To: harryproa@yahoogroups.com.au
> Subject: [harryproa] Re: Schooner v. Unarig
>
>
>
> I would think that canting the masts to leward would be
fraught
> with
> problems. I can just see the boat hitting bridge pilings, and
> other
> sailboats as it goes by. How far out to the side of the boat
> would the
> top of your mast end up being? You now have effectively
> increased the
> beam of the boat at the masthead by some ammount.
>
> --- In harryproa@yahoogroups.com.au
> <mailto:harryproa%40yahoogroups.com.au> , "Rob Denney" <proa@>
wrote:
> >
> > G'day,
> >
> > You are right, the angle is more relevant than the amount.
> Same
> weight is closer to the truth, but still low, I think. We will
> be
> doing some numbers on a schooner rigged 22m Visionarry which
we
> are
> starting early next year. I will let you know the results.
> >
> > Designing a mast to break before the boat capsizes is
fraught.
> It
> implies no safety factors and some hard decisions about waves
> and
> payloads. Then you are sailing along with full sail up, a big
> gust
> hits and you fly a hull. Ease one sail and the other mast
> breaks. I
> would prefer to cant both masts to leeward 10 degrees, keep
the
> weight
> low in the windward hull and have a chance of self righting
from
> 80
> degrees, or more realistically, not be able to capsize this
far.
>
> >
> >
> > regards,
> >
> > Rob
> >
> >
> > Oops.
> >
> > There is an error in my calculation.
> >
> > The weight of each mast is not 1/((2^.5) * (2^.5)) as shown
> below. It
> > should be 1/((2^.25) * (2^.25)). This is because the luff is
> being
> > reduced by 2^.5, which means that the reduction in weight is
> square
> > root (2^.5) = 2^.25.
> >
> > So with the schooner sail the weight of the luff portion of
> the
> > mast is now 1 / ((2^.25) * (2^.25)) = 1/2^.5 = .707. And for
> two
> > masts it would be 2*.707 = 1.415.
> >
> > However the force on each mast is still 1/2 of the force on
a
> unarig,
> > so we can still reduce (I think) the diameter of each mast
by
> 1/2^.5.
> > This gives the total weight as 2/(2^.5)(2^.5) = 1.
> >
> > Hopefully this is a bit closer to the truth.
> >
> > Also, I was looking at the same angle of deflection - not
the
> distance
> > of deflection, on the assumption that what was relevant was
> the angle
> > at the top of the mast. The link quoted gives that the angle
> is
> > proportional to the square of length and radius, whereas
> distance of
> > deflection is proportional to the cube. Should we be
concerned
> here
> > with angle or distance of deflection?
> >
> > One other point, on a cruising boat after a drama with 1
sail
> up and
> > one down, do we really want to have 1 mast pointing up or 2
> masts
> > pointing down? If the former, perhaps the breaking strenght
of
> one
> > mast should be less than the weight of the boat.
> >
> > Best regards
> > Herb
> >
> > --- In harryproa@yahoogroups.com.au
> <mailto:harryproa%40yahoogroups.com.au> , "Rob Denney" <proa@>
wrote:
> > >
> > > G'day,
> > >
> > >
> > >
> > >
> > > Rob I don't mind the schooner rig, in fact on a big boat
> where a
> > mainsheet winch is required, and if the fore boom of an Easy
> rig is
> > too high to easily reach, they have a lot going for them.
> Horses for
> > courses.
> > >
> > > Herb The angle of deflection of a circular thin wall beam
is
> > proportional
> > > to the square of the length
> > > ( http://en.wikipedia.org/wiki/Deflection
> <http://en.wikipedia.org/wiki/Deflection> )
> > > and the square of the radius
> > > ( http://en.wikipedia.org/wiki/List_of_moments_of_inertia
> <http://en.wikipedia.org/wiki/List_of_moments_of_inertia> ).
> > >
> > > R
> > >
> > > The formula for cantilever deflection is
> > >
> > > (Load*length cubed)/8*E*I Therefore it is a cube function
of
> > length, not a square. Halve the length, one eight the
> deflection.
> > >
> > > E is the material properties, I is the 2nd moment of area
> about
> > the neutral axis. I= pi*radius cubed *wall thickness. The
> radius is
> > also a cube function, so half the radius, 8 times the
> deflection.
> > >
> > >
> > > H
> > >
> > > However, each mast now has only 1/2 as much sail area, so
> the
> force on
> > > each mast is 1/2 of what it would be for the single mast.
> > >
> > >
> > >
> > > R
> > >
> > > Yes and no. Each mast has to be strong enough to capsize
the
> > boat, as it is possible that only one sail would be fully
> powered up
> > in a capsize scenario. This does not make each mast as heavy
> as a
> > single one as to be stiff enough they are already stronger
> than
> > required. However, depending on bury and other variables, it
> does
> > make each mast much more than half the weight of a single
one.
> On a
> > harry, the bury will be very similar, although although a
> higher
> > percentage of the overall length, which reduces the sheer
> loads
> > somewhat.
> > >
> > >
> > > H
> > >
> > > So I am confused. Is a schooner rig really about 2/3 the
> weight and
> > > cost of a unarig (ignoring sails), or have I misunderstood
> something?
> > >
> > > R
> > >
> > > I would say 3/2 is closer to reality for the weight and
> cost.
> > >
> > > regards,
> > >
> > > Rob
> > >
> > >
> > >
> > > Best regards
> > > Herb
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > ----------------------------------------------------------
> > >
> > >
> > > Internal Virus Database is out-of-date.
> > > Checked by AVG Free Edition.
> > > Version: 7.1.394 / Virus Database: 268.14.6/536 - Release
> Date:
> > 11/16/2006
> > >
> >
> >
> >
> >
> >
> >
> >
> ----------------------------------------------------------
> >
> >
> > Internal Virus Database is out-of-date.
> > Checked by AVG Free Edition.
> > Version: 7.1.394 / Virus Database: 268.14.6/536 - Release
> Date:
> 11/16/2006
> >
>

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