Re: Plywood/fiberglass Sandwich
Fiberglass isn't bad in compression either (unlike kevlar) or they'd
need something else when making whole boats of it. You can make a
kevlar canoe because the low density gives you enough increased
section thickness to make up for the weakness in compression. Most
structures you build are going to be in roughly equal tension and
compression unless you are making something inflatable or some kind
of
strut which is relatively thick so it won't buckle and is not subject
to significant side loads. Epoxy isn't very strong or stiff relative
to glass, but it keeps the glass from squirming around and it keeps
the water out. It's true that most of the stress is near the
surfaces.
I recommend a little elementary beam theory to anyone who wants to
design a mechanical anything (including a boat).
need something else when making whole boats of it. You can make a
kevlar canoe because the low density gives you enough increased
section thickness to make up for the weakness in compression. Most
structures you build are going to be in roughly equal tension and
compression unless you are making something inflatable or some kind
of
strut which is relatively thick so it won't buckle and is not subject
to significant side loads. Epoxy isn't very strong or stiff relative
to glass, but it keeps the glass from squirming around and it keeps
the water out. It's true that most of the stress is near the
surfaces.
I recommend a little elementary beam theory to anyone who wants to
design a mechanical anything (including a boat).
--- Inbolger@egroups.com, "Clyde S. Wisner" <clydewis@c...> wrote:
> The glass also holds a relatively thick coat of epoxy which does
change the
> strength but why not use thicker ply, if you're not trying to mold
a
snipClyde
>
> Richard Spelling wrote:
>
> > You would get some puncture resistance enhancement, but that's
about it.
> > Glass adds strength by being very strong in tension, so you
should
put it
> > where there is going to be the most tension, the surface.
> >
sniip
The glass also holds a relatively thick coat of epoxy which does change the
strength but why not use thicker ply, if you're not trying to mold a curved
shape. You can make the best ply around with layers of epoxy and door skins
and you could stick in a layer of glass also, but the weight goes right up
there. Clyde
Richard Spelling wrote:
strength but why not use thicker ply, if you're not trying to mold a curved
shape. You can make the best ply around with layers of epoxy and door skins
and you could stick in a layer of glass also, but the weight goes right up
there. Clyde
Richard Spelling wrote:
> You would get some puncture resistance enhancement, but that's about it.
> Glass adds strength by being very strong in tension, so you should put it
> where there is going to be the most tension, the surface.
>
> So, instead of a:
> 1/4"-6oz-1/4"-6oz-1/4"-6oz layup
> you should use a:
> 6oz-1/4"-1/4"-1/4"-6oz-6oz layup
>
> With the double glass layer wherever the most tension will be, generaly on
> the outside of the hull.
>
> Richard Spelling,http://www.spellingbusiness.com/boats
> >From the muddy waters of Oklahoma
>
> ----- Original Message -----
> From: "David Ryan" <david@...>
> To: <bolger@egroups.com>
> Sent: Friday, July 21, 2000 8:11 AM
> Subject: [bolger] Plywood/fiberglass Sandwich
>
> > FBBB --
> >
> > I was contemplating plywood planking while we drove into the city
> > last night and began to wonder if adding a layer of glass between
> > courses of plywood would do anything besides adding work, weight and
> > expense.
> >
> > What prompted this is how much stiffer the Light Scooner Margaret
> > Ellen is now that she has her 6/3 oz fiberglass skin. Would the
> > effect by multiplied in a 1/4"-6oz-1/4"-6oz-1/4"-6oz layup, or merely
> > cumulative? Do plywood and glass/epoxy have some sort of
> > complimentary nature?
>
> ------------------------------------------------------------------------
> Old school buds here:
>http://click.egroups.com/1/7081/13/_/3457/_/964186759/
> ------------------------------------------------------------------------
>
> Bolger rules!!!
> - no cursing
> - stay on topic
> - use punctuation
> - add your comments at the TOP and SIGN your posts
> - add some content: send "thanks!" and "ditto!" posts off-list.
I believe the reason for planking 1/4-1/4-1/4 on a curve is that it's easier
to bend three individual layers of 1/4 than one layer of 3/4.
In addition, complex curves pretty much require planking with small strips.
Doesn't add much strength, other than the added strength inherant in having
more ply layers, 9 instead of 5, which is non-trivial but probably not worth
the added work.
Richard Spelling,http://www.spellingbusiness.com/boats
From the muddy waters of Oklahoma
to bend three individual layers of 1/4 than one layer of 3/4.
In addition, complex curves pretty much require planking with small strips.
Doesn't add much strength, other than the added strength inherant in having
more ply layers, 9 instead of 5, which is non-trivial but probably not worth
the added work.
Richard Spelling,http://www.spellingbusiness.com/boats
From the muddy waters of Oklahoma
----- Original Message -----
From: "David Ryan" <david@...>
To: <bolger@egroups.com>
Sent: Friday, July 21, 2000 8:52 AM
Subject: Re: [bolger] Plywood/fiberglass Sandwich
> Richard --
>
> So this explains why the sheathing she's got seems to have added a
> disproportionately high degree of stiffness?
>
> Also, if I plank on a curve 1/4-1/4-1/4 rather than 3/4, am I getting
> any benefit, or just more work?
>
> -D
>
>
> >You would get some puncture resistance enhancement, but that's about it.
> >Glass adds strength by being very strong in tension, so you should put it
> >where there is going to be the most tension, the surface.
> >
> >So, instead of a:
> >1/4"-6oz-1/4"-6oz-1/4"-6oz layup
> >you should use a:
> >6oz-1/4"-1/4"-1/4"-6oz-6oz layup
> >
> >With the double glass layer wherever the most tension will be, generaly
on
> >the outside of the hull.
Richard --
So this explains why the sheathing she's got seems to have added a
disproportionately high degree of stiffness?
Also, if I plank on a curve 1/4-1/4-1/4 rather than 3/4, am I getting
any benefit, or just more work?
-D
134 W.26th St. 12th Floor
New York, NY 10001
(212) 247-0296
So this explains why the sheathing she's got seems to have added a
disproportionately high degree of stiffness?
Also, if I plank on a curve 1/4-1/4-1/4 rather than 3/4, am I getting
any benefit, or just more work?
-D
>You would get some puncture resistance enhancement, but that's about it.CRUMBLING EMPIRE PRODUCTIONS
>Glass adds strength by being very strong in tension, so you should put it
>where there is going to be the most tension, the surface.
>
>So, instead of a:
>1/4"-6oz-1/4"-6oz-1/4"-6oz layup
>you should use a:
>6oz-1/4"-1/4"-1/4"-6oz-6oz layup
>
>With the double glass layer wherever the most tension will be, generaly on
>the outside of the hull.
>
>
>Richard Spelling,http://www.spellingbusiness.com/boats
>From the muddy waters of Oklahoma
>
>----- Original Message -----
>From: "David Ryan" <david@...>
>To: <bolger@egroups.com>
>Sent: Friday, July 21, 2000 8:11 AM
>Subject: [bolger] Plywood/fiberglass Sandwich
>
>
>> FBBB --
>>
>> I was contemplating plywood planking while we drove into the city
>> last night and began to wonder if adding a layer of glass between
>> courses of plywood would do anything besides adding work, weight and
>> expense.
>>
>> What prompted this is how much stiffer the Light Scooner Margaret
>> Ellen is now that she has her 6/3 oz fiberglass skin. Would the
>> effect by multiplied in a 1/4"-6oz-1/4"-6oz-1/4"-6oz layup, or merely
>> cumulative? Do plywood and glass/epoxy have some sort of
>> complimentary nature?
>
>
>
>------------------------------------------------------------------------
>Old school buds here:
>http://click.egroups.com/1/7081/13/_/3457/_/964186759/
>------------------------------------------------------------------------
>
>Bolger rules!!!
>- no cursing
>- stay on topic
>- use punctuation
>- add your comments at the TOP and SIGN your posts
>- add some content: send "thanks!" and "ditto!" posts off-list.
134 W.26th St. 12th Floor
New York, NY 10001
(212) 247-0296
In a message dated 07/21/2000 9:<BR16:<BR02 AM
Eastern Daylight ,david@...writes:> I was contemplating
plywood planking while we drove into the city
will do least good. Depending upon thickness of the laminate, etc., the GRP
layer can add 10 tiems or more additional stiffness on the exterior of the
laminate.
This isn't to say that it is worthless in the center, just that it is nearly
so :-)
Cheers/Step
Eastern Daylight ,david@...writes:> I was contemplating
plywood planking while we drove into the city
> last night and began to wonder if adding a layer of glass betweenYou'll be putting the material on the neutral axis of the laminate where it
> courses of plywood would do anything besides adding work, weight and
> expense
will do least good. Depending upon thickness of the laminate, etc., the GRP
layer can add 10 tiems or more additional stiffness on the exterior of the
laminate.
This isn't to say that it is worthless in the center, just that it is nearly
so :-)
Cheers/Step
You would get some puncture resistance enhancement, but that's about it.
Glass adds strength by being very strong in tension, so you should put it
where there is going to be the most tension, the surface.
So, instead of a:
1/4"-6oz-1/4"-6oz-1/4"-6oz layup
you should use a:
6oz-1/4"-1/4"-1/4"-6oz-6oz layup
With the double glass layer wherever the most tension will be, generaly on
the outside of the hull.
Richard Spelling,http://www.spellingbusiness.com/boats
From the muddy waters of Oklahoma
Glass adds strength by being very strong in tension, so you should put it
where there is going to be the most tension, the surface.
So, instead of a:
1/4"-6oz-1/4"-6oz-1/4"-6oz layup
you should use a:
6oz-1/4"-1/4"-1/4"-6oz-6oz layup
With the double glass layer wherever the most tension will be, generaly on
the outside of the hull.
Richard Spelling,http://www.spellingbusiness.com/boats
From the muddy waters of Oklahoma
----- Original Message -----
From: "David Ryan" <david@...>
To: <bolger@egroups.com>
Sent: Friday, July 21, 2000 8:11 AM
Subject: [bolger] Plywood/fiberglass Sandwich
> FBBB --
>
> I was contemplating plywood planking while we drove into the city
> last night and began to wonder if adding a layer of glass between
> courses of plywood would do anything besides adding work, weight and
> expense.
>
> What prompted this is how much stiffer the Light Scooner Margaret
> Ellen is now that she has her 6/3 oz fiberglass skin. Would the
> effect by multiplied in a 1/4"-6oz-1/4"-6oz-1/4"-6oz layup, or merely
> cumulative? Do plywood and glass/epoxy have some sort of
> complimentary nature?