steveJ wrote:

Glen and all, Would you agree that the Gougeon Brother's On Boat
construction book, when discussing wood strip composites, talks only
about small boats, canoes,etc? I think they mentioned that further
research was needed and you have apparently done some of that. Also,
MacNaughtons are the only people that I am aware who have done any
published work on scaling up the scantlings that the Gougeons
initially offered. I'm curious to know if there are any other
published testing data that you know of?

There is not a whole lot of published work out there. Baltek has done
several white papers on their Duracore strip/composite, PBB has done a
few articles and I found some other research done by universities. It
has been 5 years since I did all that research so It will take some
digging to get the references. Large scale strip composite is not in
the "experimental" stage though. Several mega yachts in the 120'+ range
have been built in the last few years.

When scaling up to thicker strips, edge nailing is frequently used to
hold things in place. I think MacNaughton mentions that the nails
are not a structural element in the finished monocoque shell. I'm not
disagreeing with what you are saying. But I just wonder how scaling
from a canoe with a 1/4 inch strip thickness translates to a larger
boat of, say, 3/4 inch thickness. It seems that most of the larger
strip built boats have structural bulkheads which may come into play.

Actually strip/composite requires less interior structure by a long way
than most other methods. My 45' hull has only a single structural
bulkhead at the mast to take the transverse load of the shrouds.

Scaling up is basically a balancing act between strength and weight
using glass and wood. In a 1/4" stripper canoe with a layer of 6 oz
cloth inside and out, the wood is the major structural component and the
glass acts more to hold it together and protect the wood. The wood
carries most of the load.

As you go up the the strips act more like a core (but not completely)
and glass gets more critical. Design work gets a lot more complex. The
strips on my hull are 1 1/8" thick. The hull was simulated to examine
the stresses and each side was divided into 5 areas. In each area the
unidirectional glass oriented to the lines of force and the number of
plys and type of fabric adjusted to local requirements. The wood
carries most of the fore and aft tension forces and virtually all of the
compressive forces in all directions.

Possibly bead and cove milling, rather than square edge strips might
add enough sheer load resistance to warrant using yellow glue. My
preference on small boats is to use epoxy with micro balloons to make
sanding easier. Without the microballons the epoxy is harder than
the cedar and is difficult to sand fair. But yellow glue works too
and, at least on small boats, it is faster then waiting for epoxy to
kick so you can lay more strips in a session. I've also tried
powdered Plastic Resin glue but never had much luck with it since it
does not really bridge gaps too well. Titebond II is definitely a
Royal PITA to sand.Too rubbery. On one small boat I built I used
epoxy to edge glue the strips. The hull seems very stiff and strong.
But I have cracked the hull when hitting a rock. On another small
boat I built I used yellow glue and the hull seems more flexible and
has a "dead" sound when tapped. But I have never cracked this hull
even though I've given it some rough use. It's also only 3/16 inch
thick. Mabey flexibility is a good thing.

Bead and cove definitely helps. Besides making alignment a lot easier
iy widens the glue surface. I have found that a mix of about 50/05
cabosil and microballons makes a good sound sandable epoxy joint that is
only slightly harder than the cedar. IF the hull will be in the water
for only a few hours at a time i suppse that Tightbond would work but if
it sits in the water for days at a time the MC is going to get high
enough to weaken it.


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Glenn, I defer to your research on larger boat structures. For the 28' tri I'm
building, i did use epoxy between the core-cell planking strips.

I should have qualified my statements to small boats which are not left in the
water.
On strip canoes, as the cross-grain strength of the 1/4" cedar is negligible, the
glass carries all of the 'thwartship loads. I've not heard of many strip canoe or
kayak builders using anything but carpenter's wood glue such as Titebond. My canoes
are kept dry, if only to keep the varnish out of the sun, but that's another thread.
I've not had any print-through of the yellow glue in the seams.

To Mr. Watt's comment about the difficulty of fairing epoxy-glued structures, I can
say that i end up shaping lots of wood-epoxy glue-ups and that their epoxy glue lines
offer very little resistance to a sharp plane, chisel, scraper or sandpaper.

Glenn Ashmore wrote:

Jim Conlin wrote:
It depends on whet kind of cedar strip construction.
If the boat is 'cedar strip composite', where there are structural glass skins,
the bond between the strips is not important. The strip are simply a core,
loaded in sheer. In this case, convenience and appraeance are what matters.
Yellow wood glue is commonly used. I prefer Titebond over Titebond II. It's
more easily sanded.

I am afraid that is a major and very common misconception. I spent
quite a bit of time investigating strip composite construction before
committing to it for my hull. Besides the specifications from my
designer, I read everything I could find on the subject from Nicholson
to Gougeon to McNaughton. I also built several sample panels using
various construction methods and laminate schedules and tested them on a
CE friends precision testing press and various soak tests.

Some things I learned that need to be considered:

#1 The core needs to be as monolithic as possible. It is an important
component of a structural member. The larger the hull or the thinner the
core, the more critical it becomes. Stresses need to be transferred
between the skins as evenly as possible. If the core adhesive yields at
a lower pressure than the core material stress points develop at the
seams. While it may not be structurally critical these stress points
make maintaining a fair high gloss surface impossible.

#2 Laminating resins (including epoxy) are not totally waterproof.
While I was not able to get the MC up to the point that it would induce
rot spores, it did get high enough to weaken non-water resistant glues
like Tightbond.

3# The lighter the construction, the more important core integrity
becomes. At one extreme a glass sheathed stripper canoe or dinghy will
carry 90% of the stress in the core while a big hull like mine will
carry less than 50% in the core. In either case, scrimping on the strip
adhesive is false economy.

There is no real black and white in boat building. It is all shades of
gray made up of compromises. You can spend many hours and millions of
dollars trying to find a better way and still end up with a hull that
splits wide open with a little to much backstay tension. You can go
your own way, scrimping on costs and end up with a throw away boat or
you can follow proven modern construction techniques, save a lot of
effort and have a safe durable hull.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Mon, 05 Jan 2004 04:00:06 GMT, Jim Conlin
wrote:

Glenn, I defer to your research on larger boat structures. For the 28' tri I'm
building, i did use epoxy between the core-cell planking strips.

I should have qualified my statements to small boats which are not left in the
water.
On strip canoes, as the cross-grain strength of the 1/4" cedar is negligible, the
glass carries all of the 'thwartship loads. I've not heard of many strip canoe or
kayak builders using anything but carpenter's wood glue such as Titebond. My canoes
are kept dry, if only to keep the varnish out of the sun, but that's another thread.
I've not had any print-through of the yellow glue in the seams.

Ted Moores recommends using only plastic resin glue in his canoecraft
book. That's what I used on the 16' cedar strip prospector canoe I
built. I found it easy to work with, sands nicely and doesn't show
glue lines. It's also quite cheap to buy.
Drew

I'm away from my books, but i recollect that he'd changed from using 'plastic resin' or
epoxy to yellow glue in later years.

Drew Dalgleish wrote:

On Mon, 05 Jan 2004 04:00:06 GMT, Jim Conlin
wrote:

Glenn, I defer to your research on larger boat structures. For the 28' tri I'm
building, i did use epoxy between the core-cell planking strips.

I should have qualified my statements to small boats which are not left in the
water.
On strip canoes, as the cross-grain strength of the 1/4" cedar is negligible, the
glass carries all of the 'thwartship loads. I've not heard of many strip canoe or
kayak builders using anything but carpenter's wood glue such as Titebond. My canoes
are kept dry, if only to keep the varnish out of the sun, but that's another thread.
I've not had any print-through of the yellow glue in the seams.

Ted Moores recommends using only plastic resin glue in his canoecraft
book. That's what I used on the 16' cedar strip prospector canoe I
built. I found it easy to work with, sands nicely and doesn't show
glue lines. It's also quite cheap to buy.
Drew

Drew Dalgleish ) writes:

Ted Moores recommends using only plastic resin glue in his canoecraft
book. That's what I used on the 16' cedar strip prospector canoe I
built. I found it easy to work with, sands nicely and doesn't show
glue lines. It's also quite cheap to buy.

I would imagine if one is using bead-and-cove strips the fit has to be
tight enough for palstic resin glue. If not shaping the edges for a
bead-and-cove fit would be a waste of time and money.


--
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Glenn & Others

Many thanks for your comments, much appreciated.

Glenn. I definitely was not trying to save a few dollars on epoxy. I use
epoxy all the time -the sanding issue is my concern, a point picked up by
others. I want the boat to be finished to show the natural grain of the
wood, and ordinarily this is OK with epoxy except that I have had problems
in the past with sanding an epoxy/softwood join, even using microballoons.
I have sometimes found it difficult to get a nicely flared joint without
sanding down the wood too far. I must admit though that I like your long
sanding boards. This may do the trick. And what a boat you are building!
Congratulations on such an ambitious project. It looks like it is coming
along very nicely and I will follow your progress with interest.

Again, thanks to all (but no mention of any experience with Compumarine
plans, so if anybody out there has experience with these I would be
interested).

Regards

ken


"Glenn Ashmore" wrote in message
news:MaXJb.22984$JD6.4626@lakeread04...
I just cannot believe how many people will do ANYTHING to avoid spending
$50 for some epoxy. Enough 1/4" clear cedar strip for a decent size
dinghy or canoe will cost you at least $500.00. Do you really want to
risk that investment and your labor to save $40 or $50?

The strips are not there just to hold the glass. They provide
longitudinal stiffness. They must transfer shear loads between the two
composite skins. And they must spread impact loads. Individual strips
are not capable of doing any of those things. They have to be well
bonded together so they can act in unison. Hot melt glue is not going to
that. Liquid Nails might hold the strips together but the assembly will
not be very stiff and fairing will be a royal PITA.

You need a glue that maintains a tight stiff bond in a varying width
glue line (gap filling), does not require high clamping pressure and
that can be sanded fair without gumming up the paper. There is only one
glue commonly available to amateur boat builders that will do that: Epoxy.

Thickened epoxy is gap filling, bonds extremely well, requires minimal
clamping pressure so staples are all that is needed and it fairs cleanly.

Resorcinol would be a second choice. It would be a little less costly
but requires careful fitting to eliminate any gaps and a lot of clamping
pressure. Staples will not do it. You could only add one strip to each
side per day. Same with polyurethanes only your total cost will be more
than epoxy.

There are people on this newsgroup that will advocate anything from
wallpaper paste to curtain liner to save money but trying to save $50 on
adheasive on a $700 project is penny wise and pound foolish.

KR & CA Hunter wrote:
Has anybody bought and built from a Compumarine plan? If so, could you
advise your experiences? I would like my next boat project to be a
cedar
strip row/power boat and the John Clark plans look Ok on the web, but
they
seem a bit expensive for what are essentially a set of hull templates.

Also, can anybody advise on what type(s) of glue are suitable for cedar
strip construction. Builders adhesive has been suggested. Here in
Australia the "Liquid Nails" product is sometimes referred to as
builders
glue. Does anyone know whether this is the same product?

I would prefer to build without fasteners if possible, so any experience
out
there would be appreciated.

Many thanks.

Ken



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

I've never had that problem using microballoons in the epoxy. I also use a
hard back disk in my (makita) DA sander or a long sanding block. I use it to
fill (chink) the gaps in the old cedar strips. More of a problem (than epoxy)
is the clinch nails not sanding flush.
Greg Sefton

Glenn. I definitely was not trying to save a few dollars on epoxy. I use
epoxy all the time -the sanding issue is my concern, a point picked up by
others. I want the boat to be finished to show the natural grain of the
wood, and ordinarily this is OK with epoxy except that I have had problems
in the past with sanding an epoxy/softwood join, even using microballoons.
I have sometimes found it difficult to get a nicely flared joint without
sanding down the wood too far. I must admit though that I like your long
sanding boards. This may do the trick.

If you can get a copy of a book called: "Building the St. Pierre Dory" by
Mark White it details building 20+ foot boats using the strip plank method.
Mr. White does an impressive job with pictures and loads of information on
the entire process including which glues work and why....I would be happy to
forward excerpts from my copy if you would like.
regards, mike
"KR & CA Hunter" wrote in message
...
Has anybody bought and built from a Compumarine plan? If so, could you
advise your experiences? I would like my next boat project to be a cedar
strip row/power boat and the John Clark plans look Ok on the web, but they
seem a bit expensive for what are essentially a set of hull templates.

Also, can anybody advise on what type(s) of glue are suitable for cedar
strip construction. Builders adhesive has been suggested. Here in
Australia the "Liquid Nails" product is sometimes referred to as builders
glue. Does anyone know whether this is the same product?

I would prefer to build without fasteners if possible, so any experience
out
there would be appreciated.

Many thanks.

Ken