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• ## Re: water ballast vs lead, iron, etc

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• Guy, at your The Stiffness of an Advanced Sharpie at http://faculty.valpo.edu/gvandegr/ there is this: This axis of rotation ensures that the total area
Message 1 of 25 , Dec 1 12:21 AM
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Guy,

http://faculty.valpo.edu/gvandegr/ there is this:

"This axis of rotation ensures that the total area of this
underwater section remains constant. Close inspection of the graph
indicates that the rotation slightly increases the area under the
waterline. Hence the rotation is accompanied by a slight lifting of
the boat, which becomes important only at large angle, I believe."

What lifts the boat? How is it lifted if it remains the same mass?
(disregarding any lifting component of the forces on any sail)

I can imagine wider hull sections aft coming into play as they are
immersed (more) with increasing heel, and so perhaps lifting this
represented midships cross section. If this is the case then the
data set gained from only this representative cross section would be
insufficient to construct a generally representative model.

If this is not the case it would appear that, as the boat is not
able to just arbitrarily "lift" by some unknown means, then the
assumptions made from this represented cross section are somewhat
erroneous and therefore any further calculations based on them are
also going to be in error. My calculus skills are too rusty to
comment on your derived equations, and the insights and intuitions
gained, other than to raise the point that any initial error in
assumptions may be compounded, perhaps more than trivially so.

Graeme
• I meant to observe first that if there is increased area under the waterline at this cross section then that at first would appear to indicate more water being
Message 1 of 25 , Dec 1 12:48 AM
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I meant to observe first that if there is increased area under the
waterline at this cross section then that at first would appear to
indicate more water being displaced. If more water is displaced then
the boat is being sunk not lifted as stated.

Sail heeling forces may account for the boat being pressed into the
water, and so the increased displacement. However the experiment
involved heeling the boat by shifting fishing weights athwartships
without dynamic sail forces, and so there seems need to explain how
the extra water came to be displaced when the total mass of the boat
remained constant.

Graeme

--- In bolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
wrote:
>
> Guy,
>
> http://faculty.valpo.edu/gvandegr/ there is this:
>
>
> "This axis of rotation ensures that the total area of this
> underwater section remains constant. Close inspection of the
graph
> indicates that the rotation slightly increases the area under the
> waterline. Hence the rotation is accompanied by a slight lifting
of
> the boat, which becomes important only at large angle, I believe."
>
> What lifts the boat? How is it lifted if it remains the same mass?
> (disregarding any lifting component of the forces on any sail)
>
> I can imagine wider hull sections aft coming into play as they are
> immersed (more) with increasing heel, and so perhaps lifting this
> represented midships cross section. If this is the case then the
> data set gained from only this representative cross section would
be
> insufficient to construct a generally representative model.
>
> If this is not the case it would appear that, as the boat is not
> able to just arbitrarily "lift" by some unknown means, then the
> assumptions made from this represented cross section are somewhat
> erroneous and therefore any further calculations based on them are
> also going to be in error. My calculus skills are too rusty to
> comment on your derived equations, and the insights and intuitions
> gained, other than to raise the point that any initial error in
> assumptions may be compounded, perhaps more than trivially so.
>
>
> Graeme
>
• The more I ve pondered some emblematic examples of the extraordinarily parsimonious writing style of PCB the younger, the more I wonder at the wonder of it.
Message 1 of 25 , Dec 1 1:21 AM
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The more I've pondered some emblematic examples of the
extraordinarily parsimonious writing style of PCB the younger, the
more I wonder at the wonder of it. The vision exchanged, much said
in little ink.

There's the old adage of a picture being worth a thousand words
(here too PCB excels). Ho hum, heard that before. However I find it
remarkable how sometimes PCB has strikingly used but a few words to
describe a thousand pictures.

For example, regarding the current discussion, I believe all to do
with ballast, cross sectional shape, beam, draft, length,
metacentric height, COG, COB, GZ, deep bulb keels, though perhaps
not specifically ballast moment of inertia, was REDUCED to writing
by PCB the younger quite some time ago. One needs perhaps be a
little familiar with the context where presented, and no doubt a
rudimentary understanding of the naval design terms also helps, but
once assimilated I think a reasonable approximation of almost how
any hull is likely to perform under press of sail can be "seen" in
the mind's eye when guided by PCB's enlightening insight, so well
expressed.

PCB could explain it in two sentences. I have to repeat that, in
two (!!) sentences:

"The upright stance is possible because in spite of being narrow for
her length, she's wide for her depth under water." (FS, p81 Rondo
ll); and "But regardless of her length, a boat that is deep-bodied
for her breadth, and doesn't carry her ballast on a deep fin, will
be tender under sail." (FS, p69 Blackgauntlet ll)

This explanation takes quite a bit of unpacking, however I believe
it contains all that is required - perhaps a book or two's worth.

(Also, when mentally considering neutral ballast hull volumes simply
subtract them from the overall hull shape until they are above the
waterline.)

Graeme
• The more I ve pondered some emblematic examples of the extraordinarily parsimonious writing style of PCB the younger, the more I wonder at the wonder of it.
Message 1 of 25 , Dec 1 1:21 AM
View Source
The more I've pondered some emblematic examples of the
extraordinarily parsimonious writing style of PCB the younger, the
more I wonder at the wonder of it. The vision exchanged, much said
in little ink.

There's the old adage of a picture being worth a thousand words
(here too PCB excels). Ho hum, heard that before. However I find it
remarkable how sometimes PCB has strikingly used but a few words to
describe a thousand pictures.

For example, regarding the current discussion, I believe all to do
with ballast, cross sectional shape, beam, draft, length,
metacentric height, COG, COB, GZ, deep bulb keels, though perhaps
not specifically ballast moment of inertia, was REDUCED to writing
by PCB the younger quite some time ago. One needs perhaps be a
little familiar with the context where presented, and no doubt a
rudimentary understanding of the naval design terms also helps, but
once assimilated I think a reasonable approximation of almost how
any hull is likely to perform under press of sail can be "seen" in
the mind's eye when guided by PCB's enlightening insight, so well
expressed.

PCB could explain it in two sentences. I have to repeat that, in
two (!!) sentences:

"The upright stance is possible because in spite of being narrow for
her length, she's wide for her depth under water." (FS, p81 Rondo
ll); and "But regardless of her length, a boat that is deep-bodied
for her breadth, and doesn't carry her ballast on a deep fin, will
be tender under sail." (FS, p69 Blackgauntlet ll)

This explanation takes quite a bit of unpacking, however I believe
it contains all that is required - perhaps a book or two's worth.

(Also, when mentally considering neutral ballast hull volumes simply
subtract them from the overall hull shape until they are above the
waterline.)

Graeme
• The more I ve pondered some emblematic examples of the extraordinarily parsimonious writing style of PCB the younger, the more I wonder at the wonder of it.
Message 1 of 25 , Dec 1 1:24 AM
View Source
The more I've pondered some emblematic examples of the
extraordinarily parsimonious writing style of PCB the younger, the
more I wonder at the wonder of it. The vision exchanged, much said
in little ink.

There's the old adage of a picture being worth a thousand words
(here too PCB excels). Ho hum, heard that before. However I find it
remarkable how sometimes PCB has strikingly used but a few words to
describe a thousand pictures.

For example, regarding the current discussion, I believe all to do
with ballast, cross sectional shape, beam, draft, length,
metacentric height, COG, COB, GZ, deep bulb keels, though perhaps
not specifically ballast moment of inertia, was REDUCED to writing
by PCB the younger quite some time ago. One needs perhaps be a
little familiar with the context where presented, and no doubt a
rudimentary understanding of the naval design terms also helps, but
once assimilated I think a reasonable approximation of almost how
any hull is likely to perform under press of sail can be "seen" in
the mind's eye when guided by PCB's enlightening insight, so well
expressed.

PCB could explain it in two sentences. I have to repeat that, in
two (!!) sentences:

"The upright stance is possible because in spite of being narrow for
her length, she's wide for her depth under water." (FS, p81 Rondo
ll); and

"But regardless of her length, a boat that is deep-bodied
for her breadth, and doesn't carry her ballast on a deep fin, will
be tender under sail." (FS, p69 Blackgauntlet ll)

This explanation takes quite a bit of unpacking, however I believe
it contains all that is required - perhaps a book or two's worth.

(Also, when mentally considering neutral ballast hull volumes simply
subtract them from the overall hull shape until they are above the
waterline.)

Graeme
• When the Shearwater (larger Dovkie)was designed I believe PCB and Peter Duff thought about water ballast. They decided on lead approx 2 inches thick, glassed
Message 1 of 25 , Dec 1 8:40 AM
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When the Shearwater (larger Dovkie)was designed I believe PCB and
Peter Duff thought about water ballast. They decided on lead approx 2
inches thick, glassed to the inside of the flat hull bottom, across to
the beginning of the turn of the bilge on each side and 2 feet or so
fore and aft. It was located at the bottom of the companionway and did
not interfere much. It added inertia, but good righting moment only
when well heeled. It represented about 500 lbs out of a total of 2200
lbs - which is still pretty light for a 28 footer.
• Graeme, You are absolutly right in observing that the lifting of the boat begins as soon as the angle deviates from zero. Hence, the linear relation between
Message 1 of 25 , Dec 1 8:54 AM
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Graeme,

You are absolutly right in observing that the lifting of the boat
begins as soon as the angle deviates from zero. Hence, the linear
relation between torque and angle is never strictly true. I believe
(hope) that this effect is sufficiently small in most boats. This
needs to be checked, either numerically or experimentally.

shifted them "leeward" from the "windward" side. There was no "wind"
of course, and the actual force of the sails on the boat are
complicated and dynamic. Though unable to model all complexities, I
believe our experiment exactly matched what computer stability codes do.

Guy
• Since the dreaded stability question has been raised again, here s a link I came about (after the last discussion ended in a fierce battle over multihulls -
Message 1 of 25 , Dec 1 10:24 AM
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Since the dreaded 'stability question' has been raised again, here's a
link I came about (after the last discussion ended in a fierce battle
over multihulls - guess I'll have to pick my words more carefully):
http://www.boatdesign.com/postings/pages/knockdown.htm

My search for rightening moment actually reveiled not only that a flat
boat without any keel at all can still be a very seaworty vessel, it
has been done for more than 3000 years:
http://www.flickr.com/photos/67816918@N00/sets/72157594372244167

As for internal ballast: the British Navy (Nelson's Navy that is) used
shingle

Patric
• Patric, No need to apologize about the Junk photos. I have long looked for something like this. And I forgive you for reposting the well known, but classic,
Message 1 of 25 , Dec 1 10:36 AM
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Patric, No need to apologize about the Junk photos. I have long
looked for something like this. And I forgive you for reposting the
well known, but classic, link on Bolger Box knockdowns.

Guy

--- In bolger@yahoogroups.com, "Patric Albutat" <albutat@...> wrote:
> http://www.boatdesign.com/postings/pages/knockdown.htm
> If everybody knows already, sorry!
>
> My search for rightening moment actually reveiled not only that a flat
> boat without any keel at all can still be a very seaworty vessel, it
> has been done for more than 3000 years:
> http://www.flickr.com/photos/67816918@N00/sets/72157594372244167
• Guy, I m missing something here. How can the boat lift in static conditions when the mass is unchanged. Lift defined by displacing less water. How is the
Message 1 of 25 , Dec 1 6:14 PM
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Guy,

I'm missing something here. How can the boat lift in static
conditions when the mass is unchanged. "Lift" defined by displacing
less water. How is the boat made lighter?

By the way, please keep on inquiring. Very interesting work.

Graeme

PS Sorry group for three repetitive posts above. Not sure how that
happened - I hit stop after send, once, as I wanted to edit
something.

--- In bolger@yahoogroups.com, "Guy Vandegrift" <guy.vandegrift@...>
wrote:
>
> Graeme,
>
> You are absolutly right in observing that the lifting of the boat
> begins as soon as the angle deviates from zero. Hence, the linear
> relation between torque and angle is never strictly true. I believe
> (hope) that this effect is sufficiently small in most boats. This
> needs to be checked, either numerically or experimentally.
• Ouch! You caught me being vague and sloppy in my language. When one chine goes down, the other one comes up. But in my defense, the center of the bottom does
Message 1 of 25 , Dec 1 7:25 PM
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Ouch! You caught me being vague and sloppy in my language. When one
chine goes down, the other one comes up. But in my defense, the
center of the bottom does "lift" up.

I developed this insight when I was building Michalak's 4'x12' Piccup
Pram. I saw these 4'x8' Styrofoam slabs (maybe 3" thick) in a home
improvement store and wondered how one would behave if it rested
(empty) on water. By my stiffness formula, the empty slab would be
very stiff, but only at very, very, small angle. Once the bottom
lifted above the water, a slight breeze would flip it over.

A typical Advanced Sharpie might resemble this slab. When I first
started looking at boat hulls on the internet, I was surprized by the
shallow draft.

--- In bolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
wrote:
>
> Guy,
>
> I'm missing something here. How can the boat lift in static
> conditions when the mass is unchanged. "Lift" defined by displacing
> less water. How is the boat made lighter?
>
• ... You are quite right that the stiffness of a flat-bottomed hull disappears at quite small angles of heel. When Bolger did some after-capsize stability
Message 1 of 25 , Dec 2 5:21 AM
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> By my stiffness formula, the empty slab would be
> very stiff, but only at very, very, small angle. Once the bottom
> lifted above the water, a slight breeze would flip it over.

You are quite right that the stiffness of a flat-bottomed hull
disappears at quite small angles of heel. When Bolger did some
after-capsize stability studies of the Martha Jane sharpie, he found
that the point of no return was much higher than expected, maybe 45 or
50 degrees. AS-29 was not compromized by thoughts of trailering and is
more heavily ballasted.

High topsides and careful attention to hatches and other openings are
required for safety. You can see this in production boats with inside
ballast too, such as the water-ballasted 25-footers from Hunter and
Catalina.

Peter
• My boat stability project has reached the point where it must go dormant till I get collaborators. The price a professor pays for doing trivial research is
Message 1 of 25 , Dec 2 12:42 PM
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My boat stability project has reached the point where it must go
dormant till I get collaborators. The price a professor pays for doing
"trivial" research is that it must focus on education. Anybody who can
contribute is welcome to apply.

I need someone who either did well in high school physics, geometry,
and algebra, or who has strengthened these skills in college. Most
college graduates have poor writing skills, but anybody who can
write can be prinicpal author on a paper to AJP (American Journal of
Physics). A high school student with a parent who can write, along
with somebody who knows boats and can run hull stability software,
would make an awesome team! Though most papers in AJP have one author,
I think they will like the diversity and perhaps even physical
remoteness of those who solve this problem.

Guy

See "Stiffness of an Advanced Sharpie" on my homepage at
http://faculty.valpo.edu/gvandegr/.

P.S. AJP pays authors ten times what I hear they pay contributors to
MAIB, which is nothing.
• Hmmm..... ten times nothing is ... NOTHING! Bob ... Check out the all-new Yahoo! Mail beta - Fire up a more powerful email and get things done faster.
Message 1 of 25 , Dec 4 10:42 PM
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Hmmm..... ten times nothing is ... NOTHING!
Bob

---------------------------------
Check out the all-new Yahoo! Mail beta - Fire up a more powerful email and get things done faster.

[Non-text portions of this message have been removed]
• That s why I am not interested in writing the paper myself. Re: idea for overbuilt boat . I know I am mixing threads, but both are linked by my attempt to
Message 1 of 25 , Dec 5 8:40 AM
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That's why I am not interested in writing the paper myself.

Re: "idea for overbuilt boat". I know I am mixing threads, but both
are linked by my attempt to collaborate via internet with a group of
kids, somewhere in the world. I think the LNS on that project is a
12-ft "overbuilt" dinghy out of 0.25in by 1.5in lathe sticks (the
cheaper the better). Instead of a double-transverse layer, consider
a cross-stitched "weave" of long transverse sticks with longitudinal
sticks only a few boardwidths accross (short to permit clamping).
That should solve the buckling problem.

They say the hull is only a third the cost of a boat. I bet if we
cut the cost of the hull by a third, people will find ways to cut the
other 2/3s by 1/3. Both projects are long-range and admittedly long-
shots, justified by the idea that this is educational, and not too
dangerous if the work is done by WELL SUPERVISED middle or high
school kids. This is more fun and a lot more usefull than most of
the stuff I wrote for AJP.

Guy

--- In bolger@yahoogroups.com, Bob Slimak <otter55806@...> wrote:
>
> Hmmm..... ten times nothing is ... NOTHING!
> Bob
• Careful on the lath. The stuff one bought forty years ago was fine wood; continuous lengths with few flaws. I used it for model RR roadbed. A few years
Message 1 of 25 , Dec 5 12:39 PM
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Careful on the lath. The stuff one bought forty years ago was fine wood; continuous lengths with few flaws. I used it for model RR roadbed. A few years later the only sticks I could find were made up from short segments joined with finger splices. It didn't bend and it broke if you looked at it funny. Probably still adequate for rose vines, but worthless for the task I wanted.

As for collaboration, don't you first have to find someone who is as enthusiastic about the idea as you are?

Roger
derbyrm@...
http://home.insightbb.com/~derbyrm

----- Original Message -----
From: Guy Vandegrift
To: bolger@yahoogroups.com
Sent: Tuesday, December 05, 2006 11:40 AM
Subject: [bolger] Re: water ballast vs lead, iron, etc

That's why I am not interested in writing the paper myself.

Re: "idea for overbuilt boat". I know I am mixing threads, but both
are linked by my attempt to collaborate via internet with a group of
kids, somewhere in the world. I think the LNS on that project is a
12-ft "overbuilt" dinghy out of 0.25in by 1.5in lathe sticks (the
cheaper the better). Instead of a double-transverse layer, consider
a cross-stitched "weave" of long transverse sticks with longitudinal
sticks only a few boardwidths accross (short to permit clamping).
That should solve the buckling problem.

They say the hull is only a third the cost of a boat. I bet if we
cut the cost of the hull by a third, people will find ways to cut the
other 2/3s by 1/3. Both projects are long-range and admittedly long-
shots, justified by the idea that this is educational, and not too
dangerous if the work is done by WELL SUPERVISED middle or high
school kids. This is more fun and a lot more usefull than most of
the stuff I wrote for AJP.

Guy

--- In bolger@yahoogroups.com, Bob Slimak <otter55806@...> wrote:
>
> Hmmm..... ten times nothing is ... NOTHING!
> Bob

[Non-text portions of this message have been removed]
• Thanks for warning me about lathe. I would want to do any scarfing myself. Regarding the enthusiasm problem, middle school kids can get enthused about
Message 1 of 25 , Dec 5 1:48 PM
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Thanks for warning me about lathe. I would want to do any scarfing
myself. Regarding the enthusiasm problem, middle school kids can get
enthused about anything. I just have to verify that the middle school
is aware of the safety issues. Also, a novice amateur boatbuilder
might like the idea of an overbuilt dinghy. I didn't regret
overbuilding my Piccup Pram until I tried to lift it. Guy.

--- In bolger@yahoogroups.com, "derbyrm" <derbyrm@...> wrote:
>
> Careful on the lath. ...
> ... don't you first have to find someone who is as enthusiastic
about the idea as you are?
>
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