Is Balsa really that bad ??

Boston

It has to be even more waterproof more than that. All the epoxy resin spec sheets I've looked at (and I looked at a LOT back in the day ) showed less than .1% weight gain (water intrusion) after a one week boil. I never saw a specification with a more precise number than the "less than .1%" figure, which may mean that the actual precise number is even lower than that, but the standard test method does not make it practical to quantify amounts smaller than .1% . It is basically zero for all practical purposes.

UV is not an issue; we can deal with UV by covering or using a UV stable formulation. Yes they make those; what do you think they use to attach Chattahoochee stone? It's clear epoxy designed to hold up outdoors. They use this same family of epoxy resins to make tile grout and stone facia adhesive, all for outdoor 'engineering grade' use in constant sun. The Epon 8000 series was advertised for this.


Jimbo

 

well as I said
dont quote me on that
still
it seems the logical thing to do if your after an heirloom piece to use materials that are seriously rot resistant and sacrifice some of the initial ease of maintenance or construction

Balsa apparently has some good qualities and some bad in this regard

something Ild be curious about is if the varying thermal expansion qualities of different materials found in the laminate are not a primary cause of delamination rather than impact or overloading the surfaces
those hot and cold cycles have a real habit of tearing stuff apart over time
and most of the time boats are just sitting in the sun

 

Boston,

Here in San Francisco there is a very small change in temperature. No more than 10 or 15 degrees. Our balsa boats do just fine. You may be on to something.

Beau

 

Balsa as discussed in this thread means end-grain balsa core. Because of the architecture of the construction, thermal expansion is not going to be much of an issue, even with very divergent Cte between core and skin. The Gil flooring used in many commercial aircraft uses balsa core with aluminum skins. That has to be a pretty divergent Cte, yet those panels are known for their durability and damage tolerance. One very good thing about balsa coring is that it maintains very good compressive strength even after a crush failure. This is not at all true of honeycomb, and less true for the rigid foams.

Jimbo

 

Boston,

Wood expansion and contraction may have something to do with delamination, but the amount of expansion is pretty minimal. The linear coefficient of thermal expansion properties of eng grain balsa is in/in/degree F - Longitudinal 10.5X10^-6 compared to 20X10-6 for a difference of 9.5X10-6 in/in/Degree F. Written out this is .000,009,5 inches difference per degree F. If we assume that the materials were originally layed at 70 degrees that gives a normal service range of maybe 70 degrees up or down. So the lagest material thermal expansion from 0 to 140 would be .0000665 inches. While measurable this is such a small difference I can't see it causing delamination on its own.

 

I felt guilty as I was writing the Whaler thing, Jimbo. That's why I wrote it as a "tangent", because I didn't think of it as a core but wanted to point out the example somewhere. You caught me. I would have thought it was a "non-expanding" type pour-foam though.
In the land of freeze/thaw cycles here, I have seen these dang things weigh...I don't know, as much as one can imagine a high dollar boat full of wet mush weighing. Still "UNSINKABLE" - Yay!!! Cored construction, in general, is given the supreme test here.
Boston, that time of year here. Four black cod longliners showed in Homer this week, gettin' ready to go out west, I 'spose. The average age was a spry EIGHTY!

From the Time of Czars
and still making a living

I'll try to get a pic tomorrow of all four - Not all as pretty as the Polaris, not all schooners, but on one of these guys, you are sung a song to sleep and sleep well in anything I have seen Mother Nature dish out. Steel is the only thing that can compare, IMO, and IT doesn't talk you down from your fears and it sweats on you.

 

Too many people working with materials that have very little or no experience. You do a lousy job so you blame the material. Nothing wrong with Balsa.

 

Tauruck
Im inclined to agree

sorry just in from the club so not in the best of condition to elaborate
but ya
craftsmanship is key

cheers
B

 

I was under the impression that no resin is 100% water proof including epoxy which is approx 98%. After reading the discussion here I decided to check the data sheets that I have.
SP Ampreg 22; hardener depended range is 1.4 - 2.3% water absorption for ambient cure. This reduces to 0.6 - 1.9% if post cured 16hrs at 50'C. No test methods stated.
Hexion RIM 235; at 23'C for 24hrs 0.1 - 0.5% & 7 days 0.2- 0.8%.

Also another article I read quoted 35% loss in inter lamina shear strength for a polyester thin laminate after 12 month water immersion, 10% loss for epoxy laminate.
And we are discussing thin laminates used in cored construction.

Regarding laminate resin : glass ratios, dont confuse weight and volume fractions.
There are plenty of cored boats built by hand lay-up with stitched fabrics at 50:50wt resin:glass ratio, this is only 31% vol glass and 69% vol resin.
Even a very good infused laminate at 70%wt glass 30%wt resin is 50:50 by volume.
Also there are many production boats with solid laminates incorporating CSM and woven roving these will only have 20 - 25% vol glass the rest is resin.

Andrew

 

mark
would love to see some picts

 

What a load of rubbish . All and any problems will be from Bad workmanship not the fault of the balsa to get water in a core the glass has to have porous patchs and that means not enough resin and air bubbles etc in the glass , Is that good or what !
Just remember 90 percent of glass problems are caused by Bad workmanship and 10 percent is from bad choice of materials and how they are used !!

 

Three comments on Mr. Kelsall's reported article:

1) There are a "plethora of articles on the internet" claiming aliens have landed on Earth, Kennedy was shot by the CIA, whatever you like. This is NOT a credible argument for anything. I am stunned that any journalist, other than a FOX news reporter, would use the "Internet" as a source for anything. In the article, has Mr. Kelsall done his own research rather than writing an article about what a bunch of keyboard pounders are saying on the Internet?

2) While there are certainly problems with Balsa core boats, it is a tiny fraction of all the boats built utilizing this technology. Do people consider banning houses built of brick because a similar percentage have failures, no they write regulations that specify the way in which brick houses are to be built. Kelsall's logic is again flawed in the extreme.

It is trivial to build a balsa cored boat that will last for decades. There are literally thousands of them floating around all over the world, did Mr. Kelsall cite any percentages of boats with this problem, do a survey, provide any real data?

3) Do you REALLY want the government to decide what materials are to be used in boat building? Good God man, they'll decide everything should be built in double bottomed steel or something similar because it's safest. One should be REALLY careful about asking any government to regulate the design of anything.

Perhaps you could post the article or send a link to it so we could examine Mr. Kelsall's logic directly.

BV

 

I tried finding a copy on line, but with no luck. I dont feel like typing in the whole transcript, but the same sentiments can be found on his website

http://www.kelsall.com/images/articles/thecoreofthesandwich.pdf

"Get rid of the Balsa TimeBomb"

and the rest.

Re letting the government dictate boat building material - I know I wouldnt leave it to boatbuilders alone. Its not like they are paragons of quality.

 

"I know I wouldnt leave it to boatbuilders alone." Okay, Mr. "Unsafe at Any Speed", We could open a can of worms here!

 

I dont know why ?. Just a quick check of a large percentage of boat problems discussed in these forums, from rotting plywood to bad welds in steel, to engine problems .... goes on and on, making fascinating reading.

Try it - you'll love it!