The origins of vertical grain balsa coring

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bcooke
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The origins of vertical grain balsa coring

Post by bcooke »

I stumbled across this article online about Everett Pearson.

http://www.acmanet.org/cm/historical/do ... rt%201.pdf

Despite the myths of fiberglass boats being 'overbuilt due to ignorance of fiberglass strength' that we have all heard so much about, the article mentions Everett's engineering perspective and the fact that they actually knew quite a bit about what they were doing.

Here is an interesting quote (to me) I knew the early Tritons didn't use end grain balsa but this fills in some of the blanks.
When we first started with Triton, we
didn’t know how to stiffen the deck.”
Pearson explains. “We’d take the three-inch
diameter cardboard tubes the fiberglass
came in on, slice them in half, place them
over the deck, and lay fiberglass over them.
But it became difficult to get a nice interior
finish, so we started using longitudinal
strips of balsa as our core material.”
First the trial, then the error. Pearson
found that if water seeped through a deck
fitting, it migrated along the balsa grain
and delaminated the bond. He then took
several pieces of balsa, glued them
together and sliced off the ends to make “end grains,” so the
grain ran perpendicular to the laminate. This blocked water
migration. A salesman from the balsa supplier, Baltek, spotted
the paste-and-cut procedure one day while visiting Pearson’s
plant. He took the idea back to Baltek, and the company started
producing end grain, contoured core.
But by the time Pearson was approached to build the infamous
J/24s in the mid ‘70s, and even though he’d amassed a wealth of
knowledge in mechanically testing mostly industrial FRP parts,
not everyone was convinced balsa was a panacea for stiffening
fiberglass hulls. In fact, there was still a lot of resistance and
concern for water migration and rotting. But, “for impact resistance
and stiffness, balsa wood wins hands down,” Pearson
proclaimed. And he set out to prove his point. He made up an
end grain panel, drilled a few holes through it, anchored it to
some blocks, and submerged it in the Kickemuit in front of his
house. During low tide, the panel came up for air for about an
hour. Three years later he pulled the panel out of the river and found virtually no water penetration.
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Post by Tim »

Ev Pearson knew what he was doing, but clearly made some early mistakes. Any new product goes through a trial-and-error phase, and Pearson learned from the mistakes and changed things progressively as time went on. Admitting the mistakes and growing as a result of them only enhances Pearson's engineering prowess.

Note that this is still a dynamic process with all boatbuilding: the status quo is forever changing, being re-engineered and improving. No one knows it all, nor will they ever. And knowing that one doesn't know it all is perhaps the wisest attitude one could ever take.

Note also that the old NETA recording of Ev Pearson's talk from the late 70s or early 80s, which many of us have heard, also refers specifically to the fact that back in the day the were indeed engineering the strength of these boats to specific levels, and weren't just guessing and overbuilding. This doesn't mean they got it all perfect, but at least in Pearson's case boatbuilding wasn't the sheer guesswork of the lore and legend. Quite the contrary, and this is well documented.

Time and experience have shown that the so-called "bulletproof" nature of the early fiberglass boats simply isn't so. Hulls are thick but weak for their weight; obviously the early cored decks left a lot to be desired. These were pioneers of an industry, though, and the mere continued existence of these throwaway boats from 40+ years ago is impressive testament to their basic goodness despite the hiccups along the way.

I greatly respect Ev Pearson. He made, and continues to make, impressive contributions to the fiberglass boatbuilding industry, yet has always remained humble and ready to embrace growing new technologies despite the risks involved.
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Post by tikvah59 »

That's right - now that you mention it, my foredeck had longitudinal balsa in it when I had to recore a section a few years back. It was pretty efficient at wicking water! I guess that means they made the change sometime after 1960.

Regarding the hull thickness: if Pearson made them as thick as they did by design, why did hulls subsequently get thinner? Of course there was a motivation to cut costs, but was the strength that Pearson designed for was found to be excessive/unneeded?

Mark
Last edited by tikvah59 on Wed Nov 12, 2008 7:20 pm, edited 1 time in total.
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Post by bcooke »

My sense in general is that Ev started off with rough engineering data and it got better as time went on. I am also not so sure that the builders on the floor were following directions to the letter. I have heard a story about the workers, fearing a slow down and lay-off put in extra layers of glass just to stay busy longer. I have no idea if this is true or whether I am adding to the fog of myth.

I think I will record the fact that Tikva had longitudinal grain balsa. Maybe we can find out when the change occured. I vaguely recall Figment having longitudinal coring as well. That would place the change after #78 and most likely sometime in 1960. There is some confusion on hull#'s and dates but Tritons as late as #194 have been reported to have been built in 1960.


Yeah. I am a nerd.

Tim, did you ever note the deck coring in #100?
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Post by tikvah59 »

I think I will record the fact that Tikva had longitudinal grain balsa.
As long as you promise to spell Tikvah with an "H" :-) It's the transliteration of a Hebrew word (meaning "Hope") so the spelling of the word itself is open to some interpretation. However, in this case it's the Hebrew version of my daughter's middle name, and she spells it with an H.

Thanks, Britton, for the possible explanation of the change in hull thickness. Another compilation I'd love to see would be a gathering of all the legends surrounding the Pearson factory. There are some good stories there, true or not.

Take care,
Mark
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Post by jhenson »

Britton,

I can say with absolute certainty that #114 (1960) had long grain balsa for deck core.

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Post by Robert The Gray »

That production method must have been the one adopted by Aeromarine out here. I had half round cardboard tubes to support my un-cored side decks, and foredeck. The layup was an average of 5/8", then maybe two layers of cloth over the tubes. Nothing in the cabin top, but an athwartships tube under the bridge deck. My old boat is a 1960.

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Post by bcooke »

heh,

Robert, I read about the cardboard tubes but I thought that was a method that was being tested. I didn't realize actual boats were 'cored' with cardboard tubing.

Joe, thanks for the input. I will make an entry.

Mark, Tikvah. :-)
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Post by Tim »

tikvah59 wrote:Regarding the hull thickness: if Pearson made them as thick as they did by design, why did hulls subsequently get thinner? Of course there was a motivation to cut costs, but was the strength that Pearson designed for was found to be excessive/unneeded?
I think improved understanding of the materials, better resin to fiber ratios, the continual learning process and re-engineering that the article eludes to, and other factors gained from experience probably led to the changes, along with, of course, the need to stay at a certain cost point. The thinner laminates are probably as strong or stronger, in an ultimate strength comparison, as the thick, resin-rich ones. I think they found (just as builders have been discovering ever since) that they could retain the same desired strength characteristics with less material.

Anyway, there's not really any consistency, thick-or-thin wise, to the progression of hulls over the years, though the general trend seems to be a bit thinner at the end of the production run--but this is not a hard-and-fast rule by any information that I've seen.
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Post by Tim »

bcooke wrote:Tim, did you ever note the deck coring in #100?
Longitudinal planks.
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Post by Ric in Richmond »

1961 pearson alberg 35 has balsa planks as well.

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Post by Hirilondë »

I think everyone understands the point of this thread, but the title of it is wrong. Vertical grain lumber is lumber that is sawn at approximately right angles to the annual growth rings. Vertical grain boards are more stable, are less likely to warp or shrink and tend to hold paint better than flat grain boards. This might seem like a petty comment, but to a wood nerd it isn't.
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Post by bcooke »

Of course. End Grain Balsa is the correct terminology.

The grain is oriented vertically. My mistake.
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Post by Zach »

My 1961 Triton #101... also has the remnants of longitudinal balsa planks. (Grin)

The odd thing, is that the planks themselves are tapered at the edges. I wasn't expecting that when I started sawing...
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Post by bcooke »

Hmmm... I thought #101 was built out of sequence and I have a note saying it was delivered new on 04/01/1961.

Maybe the end grain balsa came in later than I thought.
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