[bolger] Re: Solid wood vs. plywood

No mechanical fastenings were used.
Clamps were used to apply pressure for curing....

Results of identical test with Weldwood plastic resin glue:

CDX plywood, brokc in glue, pulled a small amount of ply out
soft pine (end grain), broke in glue line
soft pine (edge grain), broke in soft pine, 1/4 from joint.

Jim Michalak wrote:

>
> Richard Spelling wrote:
> >
> > Results from destructive testing of edge glued plywood and pine.
> >
> > Condition:
> > Four 3/4 x 3 x 5 pieces of wood, 2 CDX plywood and 2 soft pine
> > Edge glued along long side to 1/2 inch BC pine, C side.
> > Allowed to cure 48 hours
> >
> > CDX plywood, ProBond foaming polyurethane glue
> > - failed on glue line
> > soft pine, ProBond foaming polyurethane glue
> > - failed on glue line
> > CDX plywood, epoxy thicked with wheat flour
> > - failed in 1/2 plywood. (ripped a good chunk out)
> > soft pine, epoxy thickend with wheat flour
> > - failed in soft pine, (split about 1/4 inch from glue line)
> > (wood "primed" with 50% acetone thinned epoxy)
> >
> > Conclusions:
> > USE EPOXY
> > Bulkhead stringers made of plywood instead of dimensional lumber will
> > work fine. The glue used is much more important than any "end grain
> > glue" problems.
> >
>
> Sounds like a valid test to me. But you didn't mention whether you used
> nails or screws into the plywood end grain. Remember that the framing is
> supposed to provide something to nail or screw into as you assemble the
> boat. If you can assemble it otherwise, you might as well go taped seam
> all the way. If you can get good mechanical fastenings into the framing
> then you can get by with simpler glues, although epoxy seems always to
> be best.
>
> JIm

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To Pippo and others interested in the plywood vs solid wood question:

There seem to have been some genuine concerns raised about the
substitution of ply. I have another alternative that has not yet been
discussed. It might be too labor intensive, and I still don't know if even
with the extra labor if the result would be safe. Basically, I suggest
thinking about using ply, but the pieces of ply could be oriented at 90
degree angles to each other similar to how a plywood "I "-Beam is made.
Visualize a piece of ply in front of you with the 2 1/2 inch vertical
dimension facing you, length (going from your right to your left) as long as
needed. This is the side of the ply, so you are looking at the solid face.
At the top and bottom of this solid face would be glued a 3/4 inch thick
piece of ply placed so that the end grain (or really "side grain") is facing
toward you. These two pieces are glued on to the main piece giving a top
and bottom "cap" . This is similar to how 'I'"-Beams for deck support are
made. Thie caps would be screwed and glued to the sides with the face of
the caps adjacent, not the end grain of the ply. , therefore I would
anticipate it would be more stable than having the screws going into the end
grain of the ply. An awful lot of extra work but...? Regards, Warren

Bolgeristas, You may be able to make a glued joint with plywood framing that would hold as well as with solid wood, but I can foresee some problems during assembly. When you are bending a large pre-fabricated side panel and attaching it to the bulkheads, the drywall screws are under great tension until the glue sets. Think of the bow transom of a Micro or Martha Jane. You would definitely want those pieces framed with solid wood.

Bill Jochems

Results from destructive testing of edge glued plywood and pine.

Condition:
Four 3/4 x 3 x 5 pieces of wood, 2 CDX plywood and 2 soft pine
Edge glued along long side to 1/2 inch BC pine, C side.
Allowed to cure 48 hours

CDX plywood, ProBond foaming polyurethane glue
- failed on glue line
soft pine, ProBond foaming polyurethane glue
- failed on glue line
CDX plywood, epoxy thicked with wheat flour
- failed in 1/2 plywood. (ripped a good chunk out)
soft pine, epoxy thickend with wheat flour
- failed in soft pine, (split about 1/4 inch from glue line)
(wood "primed" with 50% acetone thinned epoxy)

Conclusions:
USE EPOXY
Bulkhead stringers made of plywood instead of dimensional lumber will
work fine. The glue used is much more important than any "end grain
glue" problems.

Richard wrote:

>
> Looks like some test joints are in order. Most of the force on a bulkhead is
> compression, but it won't hurt to make a couple of sample joints with
> dimensional and with ply and see how the glue holds.
>
>monica@...wrote:
>
> > For my 2 bits (and not having seen the plans) I'd stay away from the
> > plywood stringers. You will have one face side gluing nicely,
> > contrasted with the "middle layers" side thats half end grain. I just
> > don't trust glue on end grain no matter how many thousands I've spent
> > on that glue.
> >
> > The same applies if you use screws or nails, they just will not hold in
> > end grain.
> >
> > In his earlier designs (pre-instant boat) the chine logs were oft 3/4 x
> > 1 3/4 as these could be ripped off the nearest (and cheap) 2x4. Though
> > after a recent trip to Home Depot I'd get the widest 2 by framing piece
> > I could and if I only throw half away consider it well and good.
> >
> > Incidentally, my first mast was made from 2 very nice 2x4's glued back
> > to back. Too bad I missed a rather nasty knot just at the partner.
> > Hence my need for a second identical mast, though this time no 2x4 was
> > worth any price. Would up using 2 2x6's and throwing much in the trash
> > bin.
> >
> > ------------------------------------------------------------------------
> >
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>
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>
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Pippo, Good. Your boat should be very durable. I too am a good swimmer, also, I always wear my buoyancy vest every time. Seriously. I have experienced being suddenly outside the chines of my boat in the Gulf of Mexico. Alone. Exhausted. Unable to board the boat because of my weakness and the interference of my buoyancy vest and afraid to remove the buoyancy vest for fear of drowning in the beautiful clear water. Fortunately, the water was not cold, although it seemed so at the time; and, in what seemed like a very long time, I regained enough strength to board my boat again. It is definitely not the kind of experience I would wish to have in common with a member of this group! Or, anyone else, for that matter. Best wishes, Bill bianc-@... wrote:original article:

Bill - gosh, when reading such sentences we do have well established procedures to follow in order to avoid bad luck (scratch, scratch!)! However, my boat will be totally epoxy glued and FG/epoxy sheated. I'll make FG/epoxy seams at all bukheads and chines. I'm also a good swimmer, and I'll wear a buoyancy vest every time ;-) ! Best, Pippo flyerus-@... wrote: However, in this instance, I believe the builder is not contemplating encapsulating the wood members of his boat, depending instead upon the holding power of screws into the endgrain of the core layers of plywood and glue. Since the investment in time and money is going to be significant in building the boat, I would consider it far more economical to find a substitute solid wood for the wood members in question. At least the boat will last many more seasons and you may even avoid drowning. A really crappy way to end a beautiful, or even a nasty, day on the water! Best wishes, Bill

flyerus-@... wrote: The idea of substituting plywood for solid wood members of stringers and frames concerns me a great deal... not for myself, but for the safety of the builder contemplating it. Without success I have tried to find engineering data on plywood panels. However, I did find a short dissertation on the strength of solid wood in tension and compression. I will include that below. Also, there is some information and some sage counsel from Chris Heintz, a renowned engineer and light aircraft designer regarding the same materials we use in building boats at the Chris Heintz Design College http://www.zenithair.com/kit-data/ht -86-3.html and http://www.zenithair.com/kit-data/ht-85-12.html and, from CBD-85. Some Basic Characteristics of Wood by N.B. Hutcheon and J.H. Jenkins, this excerpt: "The Strength of Wood The basic strength properties representative of various species are always established on the basis of a large number of tests on clear specimens in the air-dry condition. Such values obtained for white spruce, for example, show that its modulus of rupture in static bending can be about 8500 psi. The crushing strength in compression parallel to the grain at maximum load is about 5000 psi. For a variety of reasons, including the necessity to allow for variations in properties and defects such as knots and checks in commercial sizes and grades of lumber, the safe stresses that can be used in engineering design must be substantially reduced from such values by a factor of 5 or more, in accordance with carefully established formulae. Even with these reductions white spruce is seen to have a quite remarkable, safe load-carrying capacity in proportion to its weight, when it is considered that its density is only about 1/18 that of steel." Some very successful boats built with inexpensive plywood encapsulated in glass fabric and epoxy have traversed the open ocean many times. Those designers are of the opinion that the quality of the 'core' is not very important in a glass-epoxy encapsulated boat. Their success seems to indicate the validity of their claims. On the other hand, there are underway scientific investigations into the deteriorization of plastic composites in marine environments due to capillary action which causes water to invade the composite structure. However, in this instance, I believe the builder is not contemplating encapsulating the wood members of his boat, depending instead upon the holding power of screws into the endgrain of the core layers of plywood and glue. Since the investment in time and money is going to be significant in building the boat, I would consider it far more economical to find a substitute solid wood for the wood members in question. At least the boat will last many more seasons and you may even avoid drowning. A really crappy way to end a beautiful, or even a nasty, day on the water! Best wishes, Bill original article:http://www.egroups.com/group/bolger/?start=312

> Looks like some test joints are in order. Most of the force on a

bulkhead is

> compression, but it won't hurt to make a couple of sample joints with > dimensional and with ply and see how the glue holds. > > monica@... wrote: > > > For my 2 bits (and not having seen the plans) I'd stay away from the > > plywood stringers. You will have one face side gluing nicely, > > contrasted with the "middle layers" side thats half end grain. I

just

> > don't trust glue on end grain no matter how many thousands I've

spent

> > on that glue. > > > > The same applies if you use screws or nails, they just will not

hold in

> > end grain. > > > > In his earlier designs (pre-instant boat) the chine logs were oft

3/4 x

> > 1 3/4 as these could be ripped off the nearest (and cheap) 2x4.

Though

> > after a recent trip to Home Depot I'd get the widest 2 by framing

piece

> > I could and if I only throw half away consider it well and good. > > > > Incidentally, my first mast was made from 2 very nice 2x4's glued

back

> > to back. Too bad I missed a rather nasty knot just at the partner. > > Hence my need for a second identical mast, though this time no 2x4

was

> > worth any price. Would up using 2 2x6's and throwing much in the

trash

> > bin. > >

Looks like some test joints are in order. Most of the force on a bulkhead is
compression, but it won't hurt to make a couple of sample joints with
dimensional and with ply and see how the glue holds.

monica@...wrote:

> For my 2 bits (and not having seen the plans) I'd stay away from the
> plywood stringers. You will have one face side gluing nicely,
> contrasted with the "middle layers" side thats half end grain. I just
> don't trust glue on end grain no matter how many thousands I've spent
> on that glue.
>
> The same applies if you use screws or nails, they just will not hold in
> end grain.
>
> In his earlier designs (pre-instant boat) the chine logs were oft 3/4 x
> 1 3/4 as these could be ripped off the nearest (and cheap) 2x4. Though
> after a recent trip to Home Depot I'd get the widest 2 by framing piece
> I could and if I only throw half away consider it well and good.
>
> Incidentally, my first mast was made from 2 very nice 2x4's glued back
> to back. Too bad I missed a rather nasty knot just at the partner.
> Hence my need for a second identical mast, though this time no 2x4 was
> worth any price. Would up using 2 2x6's and throwing much in the trash
> bin.
>
> ------------------------------------------------------------------------
>
> eGroups.com home:http://www.egroups.com/group/bolger
>http://www.egroups.com- Simplifying group communications

For my 2 bits (and not having seen the plans) I'd stay away from the
plywood stringers. You will have one face side gluing nicely,
contrasted with the "middle layers" side thats half end grain. I just
don't trust glue on end grain no matter how many thousands I've spent
on that glue.

The same applies if you use screws or nails, they just will not hold in
end grain.

In his earlier designs (pre-instant boat) the chine logs were oft 3/4 x
1 3/4 as these could be ripped off the nearest (and cheap) 2x4. Though
after a recent trip to Home Depot I'd get the widest 2 by framing piece
I could and if I only throw half away consider it well and good.

Incidentally, my first mast was made from 2 very nice 2x4's glued back
to back. Too bad I missed a rather nasty knot just at the partner.
Hence my need for a second identical mast, though this time no 2x4 was
worth any price. Would up using 2 2x6's and throwing much in the trash
bin.

Dimensional lumber has much less flex longitudinally than ply, if that
matters.
djb

Richard wrote:

>
> I'm doing the same thing. Plywood is almost as strong longitudinaly, and

stronger in other
directions than dimensional lumber.

bianco@...wrote:

> Dear all - I was wondering whether is could be a good idea to use
> plywood instead of solid wood for bulkhead framing and eventually for
> stringers (using scarfed strips od plywood). For instance, the Bolger
> Micro framing is standardized in 3/4" thickness. I have a substantial
> quantity of okoume 3/4" plywood, and since douglas fir here costs twice
> the okoume plywood... Best, Pippo
>
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I'm doing the same thing. Plywood is almost as strong longitudinaly, and
stronger in other
directions than dimensional lumber.

bianco@...wrote:

> Dear all - I was wondering whether is could be a good idea to use
> plywood instead of solid wood for bulkhead framing and eventually for
> stringers (using scarfed strips od plywood). For instance, the Bolger
> Micro framing is standardized in 3/4" thickness. I have a substantial
> quantity of okoume 3/4" plywood, and since douglas fir here costs twice
> the okoume plywood... Best, Pippo
>
> ------------------------------------------------------------------------
> MyPoints-Free Rewards When You're Online.
> Start with up to 150 Points for joining!
>http://clickhere.egroups.com/click/805
>
> eGroups.com home:http://www.egroups.com/group/bolger
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Dear Pippo,

That is exactly what I am doing right now with my WDJ Family Schooner (which also calls for 3/4 framing). I think the only purpose for the framing is to have a wider surface for the fastening nails/screws. You will probably have to add an epoxy fillet on both sides anyway (at least I will). So far I have only added the framing to the bulkheads. Next week I will fasten the sidepanels to the bulkhead/bottom assembly. I will let you know how it works.

Bjørn

Dear all - I was wondering whether is could be a good idea to use
plywood instead of solid wood for bulkhead framing and eventually for
stringers (using scarfed strips od plywood). For instance, the Bolger
Micro framing is standardized in 3/4" thickness. I have a substantial
quantity of okoume 3/4" plywood, and since douglas fir here costs twice
the okoume plywood... Best, Pippo