Re: water ballast vs lead, iron, etc
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.
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.
--- Inbolger@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?
>
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
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
--- Inbolger@yahoogroups.com, Bob Slimak <otter55806@...> wrote:
>
> Hmmm..... ten times nothing is ... NOTHING!
> Bob
[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 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
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
--- Inbolger@yahoogroups.com, Bob Slimak <otter55806@...> wrote:
>
> Hmmm..... ten times nothing is ... NOTHING!
> Bob
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]
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]
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.
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.
> By my stiffness formula, the empty slab would beYou are quite right that the stiffness of a flat-bottomed hull
> very stiff, but only at very, very, small angle. Once the bottom
> lifted above the water, a slight breeze would flip it over.
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
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.
--- Inbolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
wrote:
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.
--- Inbolger@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?
>
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.
--- Inbolger@yahoogroups.com, "Guy Vandegrift" <guy.vandegrift@...>
wrote:
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.
--- Inbolger@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.
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
looked for something like this. And I forgive you for reposting the
well known, but classic, link on Bolger Box knockdowns.
Guy
--- Inbolger@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
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
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
As for internal ballast: the British Navy (Nelson's Navy that is) used
shingle
Patric
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
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
As for internal ballast: the British Navy (Nelson's Navy that is) used
shingle
Patric
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.
Regarding your second comment, we didn't add the fishing weights, but
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.
Enjoyed your commentary,
Guy
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.
Regarding your second comment, we didn't add the fishing weights, but
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.
Enjoyed your commentary,
Guy
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.
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.
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
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. 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
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. 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
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
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
--- Inbolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
wrote:
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
--- Inbolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
wrote:
>graph
> 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 of this
> underwater section remains constant. Close inspection of the
> indicates that the rotation slightly increases the area under theof
> waterline. Hence the rotation is accompanied by a slight lifting
> the boat, which becomes important only at large angle, I believe."be
>
> 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
> 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
>
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 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
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 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
Timbo,
As far as I can tell, your explanation of righting moment is correct.
I think one can go a bit further when talking about a flat bottomed
Bolger Box. I finally documented some stuff I did with
non-mathematical students a few years ago. See the unfinished essay
"The Stiffness of an Advanced Sharpie" at
http://faculty.valpo.edu/gvandegr/
Though the equations take more time to work through, they can also
yield insights. For example, the blunt end of prams and advanced
sharpies only slightly increase the stiffness (small angle righting
moment) of a boat. But even a slight increase in overall beam has
significant effect.
If anybody has software to calculate righting moment, let me know.
There is more to done on this project.
Guy
As far as I can tell, your explanation of righting moment is correct.
I think one can go a bit further when talking about a flat bottomed
Bolger Box. I finally documented some stuff I did with
non-mathematical students a few years ago. See the unfinished essay
"The Stiffness of an Advanced Sharpie" at
http://faculty.valpo.edu/gvandegr/
Though the equations take more time to work through, they can also
yield insights. For example, the blunt end of prams and advanced
sharpies only slightly increase the stiffness (small angle righting
moment) of a boat. But even a slight increase in overall beam has
significant effect.
If anybody has software to calculate righting moment, let me know.
There is more to done on this project.
Guy
--- Inbolger@yahoogroups.com, timbo@... wrote:
>
> There are two things that determine righting moment of a sailboat.
>
> They are:
> Center of boyancy
> and
> Center of gravity
>
--- Inbolger@yahoogroups.com, "Derek Waters" <dgw@...> wrote:
of a breach might be possible, and maybe quicker than pumping out
water tanks.
I wonder, in the olden days, if this is where the expression "getting
your rocks off" originated?
Nels
> The primary answer is, I think, that in the event of a hull breachall that
> metal ballast will tend to sink a wooden boat. The water ballastedhull will
> need much less volume devoted to floation to remain safely abovewater. Of
> course, the water ballast has a larger volume requirement than themetal,
> implying tradeoffs. The metal can sit with its mass concentratedlower in
> the same hull shape, but the foam has weight and generally needs to beuseful
> placed high in the hull to ensure an upright tendency when flooded. In a
> converted design the high position of the foam is likely to reduce
> interior volume. Some shapes and sizes suit one approach, some another.Good points. Perhaps a system to easily jettison the dumbells in case
>
> 'Horses for courses', in other words.
>
> cheers
> Derek
of a breach might be possible, and maybe quicker than pumping out
water tanks.
I wonder, in the olden days, if this is where the expression "getting
your rocks off" originated?
Nels
"... I have to wonder why a person would build a boat ...to keep water out
and then put holes inside to colect water to make it more stable."
The primary answer is, I think, that in the event of a hull breach all that
metal ballast will tend to sink a wooden boat. The water ballasted hull will
need much less volume devoted to floation to remain safely above water. Of
course, the water ballast has a larger volume requirement than the metal,
implying tradeoffs. The metal can sit with its mass concentrated lower in
the same hull shape, but the foam has weight and generally needs to be
placed high in the hull to ensure an upright tendency when flooded. In a
converted design the high position of the foam is likely to reduce useful
interior volume. Some shapes and sizes suit one approach, some another.
'Horses for courses', in other words.
cheers
Derek
and then put holes inside to colect water to make it more stable."
The primary answer is, I think, that in the event of a hull breach all that
metal ballast will tend to sink a wooden boat. The water ballasted hull will
need much less volume devoted to floation to remain safely above water. Of
course, the water ballast has a larger volume requirement than the metal,
implying tradeoffs. The metal can sit with its mass concentrated lower in
the same hull shape, but the foam has weight and generally needs to be
placed high in the hull to ensure an upright tendency when flooded. In a
converted design the high position of the foam is likely to reduce useful
interior volume. Some shapes and sizes suit one approach, some another.
'Horses for courses', in other words.
cheers
Derek
--- Inbolger@yahoogroups.com, "adventures_in_astrophotography"
<jon@...> wrote:
Somehow I have to wonder why a person would build a boat with a lot of
effort and expense invested to keep water out and then put holes
inside to colect water to make it more stable. Not to mention the
environmental issue regarding contamination of other waters with
unfriendly flora and fauna.
I would consider making the ballast boxes with closing lids and
searching some garage sales for cast iron weights that are used in
exercise machines. Many are also encapuslated with vinyl so they don't
even rattle around.
Transferring them back and forth to the boat would even give a person
a work-out at the same time:-)
Nels
<jon@...> wrote:
> As for Cartoon 40, I still would use the lead shot, mainly for theI agree Jon,
> reason given above, but also because it's simpler to build the boat
> that way, and another couple hundred pounds on the ramp shouldn't be a
> problem.
>
> Jon Kolb
> www.kolbsadventures.com/boatbuilding_index.htm
Somehow I have to wonder why a person would build a boat with a lot of
effort and expense invested to keep water out and then put holes
inside to colect water to make it more stable. Not to mention the
environmental issue regarding contamination of other waters with
unfriendly flora and fauna.
I would consider making the ballast boxes with closing lids and
searching some garage sales for cast iron weights that are used in
exercise machines. Many are also encapuslated with vinyl so they don't
even rattle around.
Transferring them back and forth to the boat would even give a person
a work-out at the same time:-)
Nels
Jon,
Bear in mind that the two advantages of dense ballast are that it lowers the
aggregate CG much more effectively than water, thereby giving a better
righting moment for a given displacement and that it provides righting
moment in a swamped boat. The second point may be the source of this thread
in the first place as PCB opined in one of his books that the water ballast
in the design he was discussing at the time would not hold the boat upright
for bailing when swamped.
btw, we marine engineers have training in fluid dynamics, but I can't speak
reliably about airplane flight dynamics without crunching numbers.
V/R
Chris
-----Original Message-----
From:bolger@yahoogroups.com[mailto:bolger@yahoogroups.com]On Behalf Of
adventures_in_astrophotography
Sent: Wednesday, November 29, 2006 9:41 AM
To:bolger@yahoogroups.com
Subject: [bolger] Re: water ballast vs lead, iron, etc
Timbo,
convinced myself that what I wrote yesterday was in error. I humbly
withdraw those remarks! It's especially embarassing since I'm an
astrodynamacist by trade and have enough physics and engineering
background to know better. Next time I'll remember the old adage that
a closed mouth gathers no foot.
As for Cartoon 40, I still would use the lead shot, mainly for the
reason given above, but also because it's simpler to build the boat
that way, and another couple hundred pounds on the ramp shouldn't be a
problem.
Jon Kolb
www.kolbsadventures.com/boatbuilding_index.htm
Bear in mind that the two advantages of dense ballast are that it lowers the
aggregate CG much more effectively than water, thereby giving a better
righting moment for a given displacement and that it provides righting
moment in a swamped boat. The second point may be the source of this thread
in the first place as PCB opined in one of his books that the water ballast
in the design he was discussing at the time would not hold the boat upright
for bailing when swamped.
btw, we marine engineers have training in fluid dynamics, but I can't speak
reliably about airplane flight dynamics without crunching numbers.
V/R
Chris
-----Original Message-----
From:bolger@yahoogroups.com[mailto:bolger@yahoogroups.com]On Behalf Of
adventures_in_astrophotography
Sent: Wednesday, November 29, 2006 9:41 AM
To:bolger@yahoogroups.com
Subject: [bolger] Re: water ballast vs lead, iron, etc
Timbo,
> Bottom lines:Last night I did some calculations exactly along these lines and
> Weight is weight.
> COG and COB determine righting moment.
> Dense materials tend to make more useful ballast because they provide
> a greater shift in the COG relative to the COB
convinced myself that what I wrote yesterday was in error. I humbly
withdraw those remarks! It's especially embarassing since I'm an
astrodynamacist by trade and have enough physics and engineering
background to know better. Next time I'll remember the old adage that
a closed mouth gathers no foot.
As for Cartoon 40, I still would use the lead shot, mainly for the
reason given above, but also because it's simpler to build the boat
that way, and another couple hundred pounds on the ramp shouldn't be a
problem.
Jon Kolb
www.kolbsadventures.com/boatbuilding_index.htm
But think of the pleasure you give to others. :-)
Roger
derbyrm@...
http://home.insightbb.com/~derbyrm
Roger
derbyrm@...
http://home.insightbb.com/~derbyrm
----- Original Message -----
From: adventures_in_astrophotography
To:bolger@yahoogroups.com
Sent: Wednesday, November 29, 2006 9:41 AM
Subject: [bolger] Re: water ballast vs lead, iron, etc
<snip>
Next time I'll remember the old adage that a closed mouth gathers no foot.
Jon Kolb
www.kolbsadventures.com/boatbuilding_index.htm
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[Non-text portions of this message have been removed]
Timbo,
convinced myself that what I wrote yesterday was in error. I humbly
withdraw those remarks! It's especially embarassing since I'm an
astrodynamacist by trade and have enough physics and engineering
background to know better. Next time I'll remember the old adage that
a closed mouth gathers no foot.
As for Cartoon 40, I still would use the lead shot, mainly for the
reason given above, but also because it's simpler to build the boat
that way, and another couple hundred pounds on the ramp shouldn't be a
problem.
Jon Kolb
www.kolbsadventures.com/boatbuilding_index.htm
> Bottom lines:Last night I did some calculations exactly along these lines and
> Weight is weight.
> COG and COB determine righting moment.
> Dense materials tend to make more useful ballast because they provide
> a greater shift in the COG relative to the COB
convinced myself that what I wrote yesterday was in error. I humbly
withdraw those remarks! It's especially embarassing since I'm an
astrodynamacist by trade and have enough physics and engineering
background to know better. Next time I'll remember the old adage that
a closed mouth gathers no foot.
As for Cartoon 40, I still would use the lead shot, mainly for the
reason given above, but also because it's simpler to build the boat
that way, and another couple hundred pounds on the ramp shouldn't be a
problem.
Jon Kolb
www.kolbsadventures.com/boatbuilding_index.htm
There are two things that determine righting moment of a sailboat.
They are:
Center of boyancy
and
Center of gravity
The center of boyancy is determined by the shape of the portion of the
hull that is currently displacing water.
The center of gravity is determined by the location and weight of
everything in the hull and the hull itself.
When a boat is sitting dead in the water with no wave or wind action on
it, if you were to take a cross section athwarships, the COB and the COG
would be aligned in a vertical line.
In a heavy displacement monohull (big lead keel), the COG is well below
the COB. As the boat heels, the COG and the COB are no longer in the same
vertical line, and this is what produces the righting moment on the boat.
In a light monohull, (a bolger light schooner, perhaps?), the COG is above
the COB. As the boat heels, the COB shifts a little bit due to the
changing hull shape displacing water, and the COG is shifted by the crew
moving to the rail. COG and COB no longer in a vertical line, thus
producing a righting moment.
In a catamaran, as the boat heels, the COB shifts radically as one hull
displaces more water than the other. This large shift in COB for a small
degree of heel is what gives cats their stiffness.
So what of water ballast vs iron vs steel vs lead vs feather pillows?
It simply comes down to where the COG is after adding the ballast. Lead
in a keel produces the largest righting moment simply because it shifts
the COG of the boat waaaaay down, without affecting the COB very much due
to the increased displacement. This is also why bulb keels are better
performing than a normal keel, because the COG shifts even farther down
without affecting the COB any more than a normal keel.
Water ballast is weight, just like any other type of weight. How
effective it is comes down to where the COG and COB of the boat is after
adding the ballast. Creating a water filled keel is silly and nobody
does it, simply because it shifts the COB as much as it shifts the COG,
making it pointless. It's even worse for feather pillows. As a keel
shape, water ballast won't help with righting moment, but it will add
mass, which may help with how the boat rides.
There is also no need for water ballast (or any type of ballast for that
matter) to be above the waterline to be effective. Ballast placed low in
a craft tends to work better not because of the waterline or displacement,
but simply because it lowers the COG more the lower it sits in the craft.
Weight is weight. A ton of feathers is a ton, and a ton of lead is a ton.
So why are feathers not used for ballast? Simply because the COG of the
boat after loading it with a ton of feathers will likely be *higher*
relative to the COB than it was before.
Water ballast on both sides of a boat vs an equivalent amount on the
centerline at the same height above the bottom will not help any more or
less, because the COG is the same in both cases. As noted in the
paragraph above, the placement of water ballast at the sides of the boat
vs the centerline will increase the moment of inertia which means the boat
won't rock as fast, but in terms of righting moment, they are identical.
Bottom lines:
Weight is weight.
COG and COB determine righting moment.
Dense materials tend to make more useful ballast because they provide a
greater shift in the COG relative to the COB
They are:
Center of boyancy
and
Center of gravity
The center of boyancy is determined by the shape of the portion of the
hull that is currently displacing water.
The center of gravity is determined by the location and weight of
everything in the hull and the hull itself.
When a boat is sitting dead in the water with no wave or wind action on
it, if you were to take a cross section athwarships, the COB and the COG
would be aligned in a vertical line.
In a heavy displacement monohull (big lead keel), the COG is well below
the COB. As the boat heels, the COG and the COB are no longer in the same
vertical line, and this is what produces the righting moment on the boat.
In a light monohull, (a bolger light schooner, perhaps?), the COG is above
the COB. As the boat heels, the COB shifts a little bit due to the
changing hull shape displacing water, and the COG is shifted by the crew
moving to the rail. COG and COB no longer in a vertical line, thus
producing a righting moment.
In a catamaran, as the boat heels, the COB shifts radically as one hull
displaces more water than the other. This large shift in COB for a small
degree of heel is what gives cats their stiffness.
So what of water ballast vs iron vs steel vs lead vs feather pillows?
It simply comes down to where the COG is after adding the ballast. Lead
in a keel produces the largest righting moment simply because it shifts
the COG of the boat waaaaay down, without affecting the COB very much due
to the increased displacement. This is also why bulb keels are better
performing than a normal keel, because the COG shifts even farther down
without affecting the COB any more than a normal keel.
Water ballast is weight, just like any other type of weight. How
effective it is comes down to where the COG and COB of the boat is after
adding the ballast. Creating a water filled keel is silly and nobody
does it, simply because it shifts the COB as much as it shifts the COG,
making it pointless. It's even worse for feather pillows. As a keel
shape, water ballast won't help with righting moment, but it will add
mass, which may help with how the boat rides.
There is also no need for water ballast (or any type of ballast for that
matter) to be above the waterline to be effective. Ballast placed low in
a craft tends to work better not because of the waterline or displacement,
but simply because it lowers the COG more the lower it sits in the craft.
Weight is weight. A ton of feathers is a ton, and a ton of lead is a ton.
So why are feathers not used for ballast? Simply because the COG of the
boat after loading it with a ton of feathers will likely be *higher*
relative to the COB than it was before.
Water ballast on both sides of a boat vs an equivalent amount on the
centerline at the same height above the bottom will not help any more or
less, because the COG is the same in both cases. As noted in the
paragraph above, the placement of water ballast at the sides of the boat
vs the centerline will increase the moment of inertia which means the boat
won't rock as fast, but in terms of righting moment, they are identical.
Bottom lines:
Weight is weight.
COG and COB determine righting moment.
Dense materials tend to make more useful ballast because they provide a
greater shift in the COG relative to the COB