Re: [bolger] Re: Technical question
Moment of inertia is determined by the cross sectional shape of a beam
perpendicular to the direction of force and is generally proportional to
the cube of the height of the beam and directly proportional to the
width of the beam. Modulus of elasticity is a constant (more or less)
for any given material.http://matweb.comis a place to start looking
for specific moduli of elasticity.
pvanderwaart wrote:
perpendicular to the direction of force and is generally proportional to
the cube of the height of the beam and directly proportional to the
width of the beam. Modulus of elasticity is a constant (more or less)
for any given material.http://matweb.comis a place to start looking
for specific moduli of elasticity.
pvanderwaart wrote:
>>There are plenty of university professors that post their
>>'finite structural analysis' course curricula online.
>>It is a little complex, but learnable
>>
>>
>
>No, no, no. We want an approach that is much simpler than that.
>
>
>
>>>: Where would I find a reference to do such calculations?
>>>
>>>
>
>
>http://boatdesign.net/articles/foam-core/
>
>This gives the approach, but does not give the constants for the
>materials you want, or give an idea of what threshold of stiffness you
>need to achieve. You can see that the math is pretty simple. The hard
>part is getting the right constants and making sure you have all the
>numbers in compatible unitsl
>
>Peter
>
>
>
>
>
>
>
>Bolger rules!!!
>- no cursing, flaming, trolling, spamming, respamming, or flogging dead horses
>- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
>- Pls add your comments at the TOP, SIGN your posts, and snip away
>- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
>- Unsubscribe:bolger-unsubscribe@yahoogroups.com
>- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
>Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
>
>
Another outstanding reference is Machinery's Handbook, published every
year. It's short on derivations of it's formulae, but it's a wealth of
info. I have the 24th edition 1992 and it's 2500+ pages. Pricey, but
very much worth it, IMO.
Bruce Hallman wrote:
year. It's short on derivations of it's formulae, but it's a wealth of
info. I have the 24th edition 1992 and it's 2500+ pages. Pricey, but
very much worth it, IMO.
Bruce Hallman wrote:
>http://emat.eng.hmc.edu/beams/cantilever_beam.htm
>
>There are plenty of university professors that post their
>'finite structural analysis' course curricula online.
>It is a little complex, but learnable.
>
>
>
>
>>: Where would I find a reference to do such calculations?
>>
>>
>
>
>
>Bolger rules!!!
>- no cursing, flaming, trolling, spamming, respamming, or flogging dead horses
>- stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
>- Pls add your comments at the TOP, SIGN your posts, and snip away
>- Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
>- Unsubscribe:bolger-unsubscribe@yahoogroups.com
>- Open discussion:bolger_coffee_lounge-subscribe@yahoogroups.com
>Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
>
>
Here is the URL to the PB issue with the keels article:
http://www.woodenboatstore.com/prodinfo.asp?number=199-096
Paul Esterle - Freelance Boating Writer
Columbia 10.7/Matilda 20
North East MD
www.captnpauley.com
pages.preferred.com/~pesterle/
http://www.woodenboatstore.com/prodinfo.asp?number=199-096
Paul Esterle - Freelance Boating Writer
Columbia 10.7/Matilda 20
North East MD
www.captnpauley.com
pages.preferred.com/~pesterle/
> The hard part is getting the right constants and making sure youTwo constants, or three.
> have all the numbers in compatible unitsl
>
> Peter
I think, that for a practical amount of accuracy,
the controlling factor is the deflection [and that is controlled
by a single constant]: The modulus of elasticity of the skin
of the 'beam'. Steel has a modulus of elasticity of about
29,000,000 psi.
The second constant, might be the shear stress of the 'web' of
the beam, [the foam core]. psi, guessing now: 100 psi?
Ultimate bending strength, should probably be checked too,
and that constant would be the bending stress of the skin.
Steel has various allowable bending stresses, depending
on things, but 60% of 36,000 psi = 22,000 psi is common.
In the real world, the variables of guessing what dynamic loading
you might encounter would overwhelm any 'hair splitting' over
the theoretical constants.
Also, don't forget that there is always the low-tech fallback
[to excessive contemplation and paper calculations].
...make a full size mockup and test it!
> > : Where would I find a reference to do such calculations?The sort of thing I had in mind as a steel strength member is shown
here:
http://www.steeltubeinstitute.org/pdf/brochures/dimension_brochure.pdf
Note that can get 8x2, 8x3, etc. See page 12 (or thereabouts). As with
the fiberglass option, you need a touch of help from an mechanical
engineer.
> There are plenty of university professors that post theirNo, no, no. We want an approach that is much simpler than that.
> 'finite structural analysis' course curricula online.
> It is a little complex, but learnable
> > : Where would I find a reference to do such calculations?http://boatdesign.net/articles/foam-core/
This gives the approach, but does not give the constants for the
materials you want, or give an idea of what threshold of stiffness you
need to achieve. You can see that the math is pretty simple. The hard
part is getting the right constants and making sure you have all the
numbers in compatible unitsl
Peter
http://emat.eng.hmc.edu/beams/cantilever_beam.htm
There are plenty of university professors that post their
'finite structural analysis' course curricula online.
It is a little complex, but learnable.
There are plenty of university professors that post their
'finite structural analysis' course curricula online.
It is a little complex, but learnable.
> : Where would I find a reference to do such calculations?
Professional Boatbuilding magazine had an article on just this topic an
issue or so ago. Don't have it right in front of me, but google PB and
ask them for a copy...
Paul Esterle - Freelance Boating Writer
Columbia 10.7/Matilda 20
North East MD
www.captnpauley.com
pages.preferred.com/~pesterle/
issue or so ago. Don't have it right in front of me, but google PB and
ask them for a copy...
Paul Esterle - Freelance Boating Writer
Columbia 10.7/Matilda 20
North East MD
www.captnpauley.com
pages.preferred.com/~pesterle/
>
> Peter: Where would I find a reference to do such calculations? The
> reason for using carbon fiber is if the keel for my boat was done out
> of pure bigerblass, it might come out too thick to work.
Fiberglass is pretty flexible, and
reason for using carbon fiber is if the keel for my boat was done out
of pure bigerblass, it might come out too thick to work. It's only
4.5 inches at the widest, and has to have a 2 inch slot open through
the middle for the rod that controls the set of the wings. At the
forward and after end of that slot the keel isn't much waider than
that 2 inch opening.
Thought I had seen a reference that the deep bulb keels for the Am.
Cup boats and the opne 60 singlehanders were mounted on a long,
skinny carbon fiber beam, which is what sparked this thought.
Finally, where would one look to buy the "strengh member" off the
shelf and then add fairing; that's intriguing; I'd have to find
something like a 7 foot by two foot by 2 or 3 inch box . . .
Gary Blankenship
> perhaps high aspect ratio struts bend too much. The calculations arePeter: Where would I find a reference to do such calculations? The
> pretty easy.
>
> I wonder if it would be possible to buy the strength member off the
> shelf, and add the fairing to make it hydrodynamic. For example, a
> 4x3" steel box beam with wooden nose and tail.
>
> Peter
>
reason for using carbon fiber is if the keel for my boat was done out
of pure bigerblass, it might come out too thick to work. It's only
4.5 inches at the widest, and has to have a 2 inch slot open through
the middle for the rod that controls the set of the wings. At the
forward and after end of that slot the keel isn't much waider than
that 2 inch opening.
Thought I had seen a reference that the deep bulb keels for the Am.
Cup boats and the opne 60 singlehanders were mounted on a long,
skinny carbon fiber beam, which is what sparked this thought.
Finally, where would one look to buy the "strengh member" off the
shelf and then add fairing; that's intriguing; I'd have to find
something like a 7 foot by two foot by 2 or 3 inch box . . .
Gary Blankenship
> So this questionThe literal answer is "yes." I believe that carbon fiber struts are
> tickled what passes for my brain: could an airfoil keel be made from
> carbon fiber, and be strong enough to support heavy lead wings?
used in some of the canting keel racers. Possibly also America's Cup
boats. Being racers, they are looking for the thinnest possible strut.
Metal ballast dropped into a fiberglass keel was one of the earliest
ideas when contruction went to fiberglass. I don't know why it's not
the usual practice now. Most of those boats had longer keels of lower
aspect ratio than today's boats. Fiberglass is pretty flexible, and
perhaps high aspect ratio struts bend too much. The calculations are
pretty easy.
I wonder if it would be possible to buy the strength member off the
shelf, and add the fairing to make it hydrodynamic. For example, a
4x3" steel box beam with wooden nose and tail.
Peter
You do not need carbon fiber, glass fiber is sufficient. Carbon fiber
is desirable when you want a high strength to weight ratio - not a
factor in a keel. If you want to overbuild it, you could upgrade to
S-glass (from the E-glass that is normally used in boats.) There are
plenty of composite airplanes flying with glass fiber wings.
I used to have an S2 9.2 meter (30') with about 5' draft fin keel.
The ballast was a lead casting encased in a fiberglass shell that was
molded right along with the rest of the hull. No keel bolts or other
structure to hold it all together, just the glass envelope. I think
that was 4000 pounds of lead. Your 1000 pounds of wings should be no
problem, given an adequate layup schedule. What that schedule would
be is beyond me.
Doug
is desirable when you want a high strength to weight ratio - not a
factor in a keel. If you want to overbuild it, you could upgrade to
S-glass (from the E-glass that is normally used in boats.) There are
plenty of composite airplanes flying with glass fiber wings.
I used to have an S2 9.2 meter (30') with about 5' draft fin keel.
The ballast was a lead casting encased in a fiberglass shell that was
molded right along with the rest of the hull. No keel bolts or other
structure to hold it all together, just the glass envelope. I think
that was 4000 pounds of lead. Your 1000 pounds of wings should be no
problem, given an adequate layup schedule. What that schedule would
be is beyond me.
Doug
--- Inbolger@yahoogroups.com, "gbship" <gbship@c...> wrote:
>
> Okay, there are steel, aluminun and carbon fiber masts. There are
> steel, aluminum and carbon fiber hulls. There are steel fin keels,
> like Bolger is planning to use on the Insolent 60. So this question
> tickled what passes for my brain: could an airfoil keel be made from
> carbon fiber, and be strong enough to support heavy lead wings? (The
> wings on my 30 footer, the prototype keel for the I-60, weigh a total
> of 1,000 pounds and I assume the I-60 wings will be much heavier.)
>
> The reason for this query is I don't weld and the boatbuilding
> company that built my metal fin did a very poor job. It required some
> pretty high precision work that came out not even close. Holes for
> pins and wing mounting bars were slightly out of position and in one
> case not even nearly perpendicular to the plane of the keel. If it
> had been installed that like, the keel wouldn't have retracted. Had
> to hire someone else to fix the problems. Anyway it got me to
> wondering about making a carbon fiber keel, especially since I may
> eventually replace the current keel. It might not actually cost any
> more once you figure the cost of hiring someone to weld up a metal
> one and the builder could control all the tolerances. Anyone know any
> references on this than would answer the questions like if the plan
> calls for a 1/8 inch steel wall, how thick would a carbon panel have
> to be? Would be be pure carbon fiber layup, or could you alternate
> with laters of fiberglass, as is done on some small sailboat masts.
>
> Just curious . . .
>
> Gary Blankenship
>
Okay, there are steel, aluminun and carbon fiber masts. There are
steel, aluminum and carbon fiber hulls. There are steel fin keels,
like Bolger is planning to use on the Insolent 60. So this question
tickled what passes for my brain: could an airfoil keel be made from
carbon fiber, and be strong enough to support heavy lead wings? (The
wings on my 30 footer, the prototype keel for the I-60, weigh a total
of 1,000 pounds and I assume the I-60 wings will be much heavier.)
The reason for this query is I don't weld and the boatbuilding
company that built my metal fin did a very poor job. It required some
pretty high precision work that came out not even close. Holes for
pins and wing mounting bars were slightly out of position and in one
case not even nearly perpendicular to the plane of the keel. If it
had been installed that like, the keel wouldn't have retracted. Had
to hire someone else to fix the problems. Anyway it got me to
wondering about making a carbon fiber keel, especially since I may
eventually replace the current keel. It might not actually cost any
more once you figure the cost of hiring someone to weld up a metal
one and the builder could control all the tolerances. Anyone know any
references on this than would answer the questions like if the plan
calls for a 1/8 inch steel wall, how thick would a carbon panel have
to be? Would be be pure carbon fiber layup, or could you alternate
with laters of fiberglass, as is done on some small sailboat masts.
Just curious . . .
Gary Blankenship
steel, aluminum and carbon fiber hulls. There are steel fin keels,
like Bolger is planning to use on the Insolent 60. So this question
tickled what passes for my brain: could an airfoil keel be made from
carbon fiber, and be strong enough to support heavy lead wings? (The
wings on my 30 footer, the prototype keel for the I-60, weigh a total
of 1,000 pounds and I assume the I-60 wings will be much heavier.)
The reason for this query is I don't weld and the boatbuilding
company that built my metal fin did a very poor job. It required some
pretty high precision work that came out not even close. Holes for
pins and wing mounting bars were slightly out of position and in one
case not even nearly perpendicular to the plane of the keel. If it
had been installed that like, the keel wouldn't have retracted. Had
to hire someone else to fix the problems. Anyway it got me to
wondering about making a carbon fiber keel, especially since I may
eventually replace the current keel. It might not actually cost any
more once you figure the cost of hiring someone to weld up a metal
one and the builder could control all the tolerances. Anyone know any
references on this than would answer the questions like if the plan
calls for a 1/8 inch steel wall, how thick would a carbon panel have
to be? Would be be pure carbon fiber layup, or could you alternate
with laters of fiberglass, as is done on some small sailboat masts.
Just curious . . .
Gary Blankenship