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Thank you for the correction Robert,

If you want to be that inclusive don't t you think you should differentiate
between displacement and non displacement hulls. And between sail power and
motor driven vessels.

I don't want to debate the various formula you present, but just as example,
displacement can't possibly be a function of strictly LWL, nor can sail area
or wetted surface. How can you ignore beam and draft. That makes no sense to
me. Care to explain?

Also I've not seen Moment of Inertia discussed relative to boat or ship
design where can I read about it.

Joel


----- Original Message -----
From: "Robert Gainer" 
To: 
Sent: Monday, August 02, 2004 9:21 AM
Subject: Re: 7/8 SCALE SEXTANTS MORE


> Joel,
> Be careful about using the word "everything" when discussing scaling a
> design. Speed varies as the square root of the waterline, sail area and
> wetted surface varies as the square of the waterline, displacement varies
as
> the cube of the waterline, stability varies as the fourth power of the
> waterline and moment of inertia varies as the fifth power of the
waterline.
> All the best,
> Robert Gainer
>
>
>
> >From: Joel Jacobs 
> >Reply-To: Navigation Mailing List 
> >To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM
> >Subject: Re: 7/8 SCALE SEXTANTS MORE
> >Date: Mon, 2 Aug 2004 07:53:04 -0400
> >
> >Let me add something that I thought of after mailing.
> >
> >In boat and ship design when you scale something up, everything changes
in
> >a
> >geometric progression rather than an arithmetic one.
> >
> >For example, one foot by one foot is one square foot, but if you increase
> >the size to two feet squared, the result is four square feet or four
times
> >greater.
> >
> >George, you're the mathematician. Doesn't the reverse hold true when you
> >shrink something?
> >
> >Joel
> >
> >
> >----- Original Message -----
> >From: "Joel Jacobs" 
> >To: "Navigation Mailing List" 
> >Sent: Monday, August 02, 2004 7:39 AM
> >Subject: 7/8 SCALE SEXTANTS
> >
> >
> > > Hello George,
> > >
> > > Some additional comments on reduced scale sextants (7/8):
> > >
> > > The small size mirrors collect less light to pass through the optical
> >system
> > > and consequently make twilight observations of stars and planets more
> > > difficult. There is another equally important disadvantage. When
taking
> >high
> > > altitude LAN sights the small surface area of the mirrors allows the
> >object
> > > to jump off the mirror more easily than with large size mirrors.
> > >
> > > In respect to the telescopes on the reduced scale sextants, they have
a
> > > small objective and ocular lens. The Freiberger scope is about 2.5 x
> >25mm
> > > compared to a normal 4 x 40 scope and passes less light through the
> >system.
> > > Again this makes observations of stars and planets more difficult.
> > >
> > > If there are any shooters amongst us, they may comment on the
preferred
> > > weight of a rifle. Some people believe that light weight rifles are
> >harder
> > > to hold on target, and less accurate even though carrying them is
> >easier.
> > > The same holds true of a sextant. A very light weight one is thought
to
> >be
> > > more difficult to use.
> > >
> > > I'm not sure of this, but I think Tamaya was the first to introduce a
> >7/8
> > > scale sextant around 1975. It was the MS 933 Venus which, when sold
> >today
> > > used, sells for about the same as a NEW Freiberger of the same size.
> > > Freiberger's list price is $600.00. Here's a link to my listing of the
> > > original Venus sextant. GO:
> >http://stores.ebay.com/LAND-and-SEA-COLLECTION
> > > It is the fourth one down. I don't know when Tamaya  discontinued
> >production
> > > of this model, but they appear on ebay fairly regularly and sell
> >quickly.
> > >
> > > Here is a link to a European Freiberger Yachtsman Sextant site since
> > > Claussen Instrument's is down.
> > > http://www.busse-yachtshop.de/dae_Yachtsextant.html Note that 600
Euros
> >is
> > > about $720 over there.
> > >
> > > If you do mostly sun sight navigation, the small size and light weight
> >might
> > > appeal to some, but the 7/8 scale sextant has never had much of a
> >following
> > > by celestial navigators.
> > >
> > > Joel Jacobs
> > >
> > >
> > > ----- Original Message -----
> > > From: "George Huxtable" 
> > > To: 
> > > Sent: Monday, August 02, 2004 5:40 AM
> > > Subject: Re: Celestaire vs Freiberger Yacht Sextant
> > >
> > >
> > > > Joel Jacobs  wrote:
> > > >
> > > >
> > > > >From my experience, if your going to do serious navigation relying
on
> > > > > twilight sights, the 7/8 scale sextants are very lacking. Their
> >optics
> > > are
> > > > > not very good, and there small size mirrors are not anywhere as
> > > effective
> > > > > when taking star sights or high altitude sun sights.
> > > > ===============
> > > >
> > > > Something about that puzzles me. Why should it be so, I ask?
> > > >
> > > > First, I should make it clear that I have never even handled such a
> >7/8
> > > > size sextant; and that observations on my own small boat have never
> >passed
> > > > beyond a plastic job, though I have used many "posh" sextants,
> >belonging
> > > to
> > > > others. So I make no claims to being an expert on sextants.
> > > >
> > > > Yet, it seems to me that if you were to shrink a sextant to 7/8 of
its
> > > > original size, and shrink its mirrors correspondingly (in both
> >directions)
> > > > while preserving the same angular field-of-view of its telescope,
then
> > > > (because the distance from the eye to those mirrors is also reduced
to
> > > 7/8)
> > > > the patch of sky that the mirrors subtend would be exactly the same
as
> > > > before.
> > > >
> > > > So, in those circumstances, why should the smaller mirrors present
any
> > > > disadvantage?
> > > >
> > > > George.
> > > >
> > > > ================================================================
> > > > contact George Huxtable by email at george@huxtable.u-net.com, by
> >phone
> >at
> > > > 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1
Sandy
> > > > Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
> > > > ================================================================
> > >
>
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