Is Balsa really that bad ??

Boston,

I know you must have some understanding of 'I' beams. Engineered wood 'I' beams have become common construction site fare as they can be made any length, have much higher stiffness to weight ratio (makes for a nice solid 2nd floor!) and save a lot of wood compared to regular lumber beams.

Think of composite sandwich structure (like balsa core with glass skins) as a sort of 'planar I beam'. The skins serve the same function as the top and bottom cap of the 'I' beam while the core material (be it balsa, foam, plywood honey comb, etc.) serves the same function as the web of the 'I' beam.

Study up on how loads pass through 'I' beams; where in the beam there is compression, tension and shear and then apply that to sandwich composite structure. Then you can understand why this or that thing is important or not important.

Jimbo

 

nah
I recommend TJI's regularly, micro lambs, glue lambs and parallel strand beams
basic engineered lumber
Im down with that although I am firstly inclined to go with a solid beam if practical ( if its going to be exposed and I want it to look like anything )
but this biz of fiberglass mat or rove in epoxy with some unknown bond between core and substrate is just a little to much
oh
Im guilty of having little experience with it
but at the same time
I just get story after story about how it fails ( pretty dam disconcerting actually )
and every time I hit the coast I see fiberglass with rot and more rot
whereas with the engineered lumber I deal with (glue and wood no fiberglass or submerged applications )
it seems to hold up just fine
the TJI's use hot pressed glue
and the glue lambs use resourcenol
microlambs
Im not sure what they use
but Ive worked with all of em numerous times and I know what the failure rate is
and I know they are not recommended for outdoor use
houses I built back in the 70's are still standing ( better be )
not sure about you guys but I guess my whole ego revolves around the stuff I build
my whole heart and soul goes into making **** what ever it is
to last
what houses Ive built
every last one of em is still standing
no fires
foundations sound
no structural defects
no rot or bentonite damage
still standing no cracks

when I build my boat
I want at least the idea of it lasting generations
but epoxy is seriously in question
and its the main ingredient in all these composites
first question and not the last is
what's it's life span
perfectly reasonable question if you ask me
and why wont the industry divulge that answer
how long will epoxy last
simple question
should be a simple answer

silence

why is the industry silent on that one
it does beg the question
is there something they know, that they dont want us to know?

whats the deal
how long does epoxy last as a bonding agent
simple question
should be a simple answer
so

whats the answer
why the silence

why wont the industry divulge what it knows concerning the lifespan of epoxy

specially in the light of all these failures in the fiberglass industry
which is also by and large dependent on the vagaries of epoxy

not trying to be difficult but if Im going to spend half a mill on a yacht
I want some real answers as to the glue holding it together
seems fare to me
some biz wants my money ok
how long will the product last
silence

that seem odd to anyone else
cause frankly it makes me a little uncomfortable

in the light of silence I can only decide to go with what is known
wood lasts for x amount of time and then you need to replace it
at least then I know what Im getting into
with epoxy
only folks who know
aren't telling
anyone else wonder why
cause I sure do

 

Most 'failures' as you refer to in the boat business are from core rot, apropos this thread, which is about that most 'rottable' of cores, balsa. If you want a boat that lasts forever, build it entirely from synthetic materials. Use good quality PVC foam and glass it over with the resin of your choice. With a synthetic material, it's not as critical to use epoxy, since the core won't rot anyway, even if a little water ingression happens at a damage point. DIAB's 'official' glue for their core foams is polyester resin based, not epoxy. Epoxy allows us to use the much cheaper natural cores (wood) that do not hold up nearly as well when assembled with poly resin. The resin will outlast the wood, if protected from UV. This does not mean a given boat will last that long, but epoxy resin failure will not likely be the reason for its obsolescence.

Jimbo

 

If using foam cores, in my experience, one ought core areas rather than the whole part (hull). I don't agree that foam is all that cool - I've done some backyard destructive testing of a manufacturer/repair facility's scraps. Whatever one attaches to foam "unzips" with alarming ease. This doesn't happen with balsa. I like how a couple of guys trying to destroy a piece of balsa cored poly seriously have their work cut out for them. Also, an impact damages more area with foam that I know. Also, you may not call it "rot" but "turn to mush" it does. I have some interior decks made of some stiff, red foam on my boat, tho. They are dry, obviously light, strong enough, and completely stable.
Tangent: I hung a typical Boston Whaler on the shop wall for more than a year and water was still draining out of the foam from the two 2" holes I cut. I don't know which of the little problem areas the water got in at but, to me, this is unacceptable.

 

hey Jim did you get a chance to read the articles presented back in the thread a ways
testing seems to show that those synthetics are just as likely if not more to fail as the balsa
something that surprised me as well
Ive always preferred natural materials and been gun shy of plastics
being mostly concerned about there toxic nature
but I to was under the impression they were at least impervious to the elements
apparently not

I mention the epoxy cause it seems like there is something someone is not telling us
deliberately
it just seemed like the most obvious one to mention

thing is with wood at least you know what your getting into
these plastics, epoxy or not, seem to come with a grab bag of serious boat killing issues

B

 

a few more articles I found
http://www.google.com/url?sa=t&source=web&ct=res&cd=3&url=http%3A%2F%2Fwww.yachtsurvey.com%2Fsearay_balsa_core_bottoms.htm&ei=j9k0StuNKobwsQOdpr3DDg&usg=AFQjCNFMXjralAzVq9tfdbo7UVHeKO-pIw&sig2=ezSZRbSinrkYjcnUDwr3cQ

actually there is a whole pile of articles located here

http://www.google.com/url?sa=t&source=web&ct=res&cd=1&url=http%3A%2F%2Fwww.yachtsurvey.com%2Fstructuralissues.htm&ei=U9w0SumCC4e6swOx5e3YDg&usg=AFQjCNETM6lTXl_zyvEGGAOQoyNeVIcnwg&sig2=c-K6Az9DHze0WkygvQGxRA

 

'Whatever one attaches to foam "unzips" with alarming ease.'
Plus when you 'thunk' balsa is sounds really good!

 

Boston,

I am a big fan of David Pascoe as well, most of his articles are well thought out and informative.

The article you linked had to do with the rott of balsa in a cored hull, which for quality builders is a big no-no, and has been for many years. The reason is that any surface below the waterline will absorb water over time (except metal hulls). It is a property of both fiberglass and wood, of course this water migrates to the core where it works its destructive magic. This is why any boat that uses a core below the waterline is questionable in my eyes, no matter what the core material is. Proper building techniques only start to core the hull a few inches above the waterline, meaning that the osmotic intrusion of water stays away from the core.

This thread started about wether balsa was a bad material for cores, and in that regard I would say that it isn't. But both foam and balsa are subject to damage from water intrusion when used as a core material. balsa from rot, foam from hydrolic erosion.

Parallel to this conversation is if a core is a sensable design for marine construction, and this seems to be what you are raising. I think like any other construction method there are trade offs that have to be made. A core makes the boat lighter, stronger, faster to build, and cheaper. However it must also be protected against water intrusion and could require significant repairs if it is damaged.

Compared to solid wood construction however the proper use of cored construction still leaves a much easier and cheaper boat to maintain. Just think about it like this... A core MAY need to be maintained over the years as water intrudes and degrages it's structual integrity. A wood hull WILL need to be maintained yearly as one board then the next rotts away.

If you feel comfortable already working in wood then it may be nice to think that it would be easier to detect problems with a wooden hull, but a few days spent banging on fiberglass will teach you the sound of a rotten core and delamination. Then it is just a process of regular inspections

 

I think it's important to remember that the 'foam-in-place' foam constriction method pioneered by Boston Whaler uses a grade of foam that nobody would even consider in a one-off build; it's strictly a production OEM deal. The poorest grade of PVC foam you could buy from a composite materials supplier will be superior to the foam BW uses. You'll not find a book on marine construction that recommends using expanding foams as structural cores either. They are recommended strictly for insulation and flotation.

Jimbo

 

Remember that there is no such thing as osmotic intrusion into epoxy resin; this is a fault strictly of polyester resin.

Jimbo

 

interesting twist
we might want to all agree on what osmosis is before we can effectively discuss it

http://captkonz.tripod.com/marineprofessional/id19.html

describes the process as it effects epoxies reasonable well

oh
some woods are extremely rot resistant
one of the best in this regards Ive been looking into a lot recently is black locust
fence posts of old growth BL have survived 100 years buried in the wet soils of the southern us

http://www.hort.purdue.edu/newcrop/proceedings1990/V1-278.html
White Oak is none to shabby at resisting decay either

biggest draw back is that both are heavy
cedar is light but takes up only slightly slower than your prom date at the punch bowl

 

Boston,

Thank you for attempting to get folks to use the terms correctly. However, this article as a number of terrible errors in it. Osmosis is a technical term with a very specific meaning, which is misused terribly by the marine industry, including this guy. For a good definition that most folks can understand see:

http://en.wikipedia.org/wiki/Osmosis

Also, the article claims that a boat ends up being "70% resin and 30% glass". This is certainly NOT the case of any high quality boat building I am aware of. Perhaps some chopper guy beater boats are this bad, but I would have been fired if I'd ever had the glass fall to less than 60% of the panel weight when I was building boats.

These errors make me question the entire article, even though I can't check on all of it.

B

 

Boston,

Water does not attack epoxy resin, no matter how long the exposure. Polyester is highly water resistant, but it is not 'waterproof'. Eventually with very long exposure time, water does indeed attack and break down cured polyester resin to some degree. Epoxy resin is waterproof. The type of blistering described on the page you referenced does not happen to cured epoxy resin.

Jimbo

 

I think you are right about that water does not "attack" epoxy in the sense that it degrades it
thats what UV is for
but neither is epoxy perfectly water proof
or I should say vapor proof
Im looking for a few articles that I read a while back concerning water vapor and various materials
I think epoxy was on top with 95% impervious
and shellac a close second with something like 90%
but dont quote me on that cuase I need to find the articles before Ild stand by those figures

gortex is a good example of how a material can be water proof but not vapor proof
the epoxy may be fine in contact with liquid water although if it breaths BP-A a relatively large molecule
it is likely to be able to breath water vapor
a relatively small molecule

Beau
feel free to critique that article
Ild be real interested to hear what your assessment would be

only experience I have with fiberglass is fixing dings and dents
( which as it turns out I am particularly good at )
one of the industry reps of extruded fiberglass told me the mix is 60/40 glass to resin
and those guys were diffidently going for an optimal mix for the lightest construction

 

Boston,

I don't believe, from looking at the West web site, that Epoxy lets vapor or liquid water through. Indeed, West Epoxy is used to make GRE (Glass Reinforced Epoxy) tanks for all sorts of terrible chemicals in addition to water and water vapor, so I really can't see how it could allow vapor though.

Regarding the article and glass to resin ratio's, here's a manual from the West web site:

http://www.westsystem.com/ss/assets/HowTo-Publications/Vacuum-Bagging-Techniques.pdf

Go have a look at section 4.2.2 where it describes the ratios of 65% glass and 35% resin. Also, these are resin's applied to "dry" glass. Now that we buy PrePreg (which is glass which has the resin already applied) it is possible to get much higher glass to resin rations. PrePreg is glass that typically has a resin that is hardened with either UV exposure or heat in an oven, not a separate chemical hardener. It comes already soaked in resin and all you do it put it where you want it and heat it up.

It's a lack of knowledge of these sorts of things that makes me doubt the article. Sure, back in the '60s and '70s we used to build boats from buckets of resin mixed with hardners that were then squished into the glass with a putty knife or brush, but that was decades ago. Boat builders don't do it that way, even if home repair folks do. There have been massive advances in construction technologies and folks who are writing papers they think are authoritative need to keep up with the times.

Beau