Balsa core...?

jlparsons · Post by **jlparsons** » Sat Sep 13, 2008 7:01 am

Ok, this may be a bit far out but stay with me...

With larger boats foam and balsa cored glass/carbon construction is common, and most of the strength from S&G boats comes from the inner and outer glass layers. So, would it not be possible to build a kayak like the sabalo (as I'm planning) from 1/4'' end-grain balsa sheet or foam, then use much thicker glass layers inside and out? I'm guessing this should give a stronger and/or lighter hull and could be substituted for plywood with very little extra work. The other advantage is that I think the sheet is pretty flexible and would be easy to stitch up, plus it cuts very easily.

Anyone done it? Or thought about it? Or am I missing a really good reason why this would be a bad idea or no advantage?

hairymick · Post by **hairymick** » Sat Sep 13, 2008 7:26 am

An Aussie boat designer/builder build a 12foot canoe out of balsa a while ago. From memory, it was a stripper, but when finished, I think it only weight 12 kgs or 12 pounds - I forget which.

The problems you might have with balsa is that is a very soft timber, and in its raw state might be a lot easier to damage before you get your epoxy onto it. in a single board form, It might also be more prone to breakage when torturing it into shape. I don't know and am just guessing here. I have never seen balsa in boards like you would require to build a S&G boat.

tx river rat · Post by **tx river rat** » Sat Sep 13, 2008 7:29 am

I did a little research on building a foam core boat, it works ok until you hit some thing the the foam has a tendency to crush and not spring back
where wood will take a harder lick and come back.
Ron

Post by **jem** » Sat Sep 13, 2008 7:52 am

As you said, you'd need thicker layers of glass for impact resistance.

We get that protect from the ply. You could build from balsa or even foam core. But to get that protection, you'd need to add lots of extra glass and end up with a boat that's heavier than the same boat built from ply.

Balsa and foam core are really helpful in composite sandwich construction and offer great benefits on boats over 25'. Then they start getting lighter than if you built the same design with ply.

jlparsons · Post by **jlparsons** » Sat Sep 13, 2008 9:05 am

I see what you mean. Might be interesting to test it though, perhaps I might try to get hold of a sample, glass it up to weigh the same as an equivalent ply & glass piece, then bash the snot out of it in a pseudo-scientific manner and see how it fares!

If I ever get around to it, I'll let you know!

Post by **jem** » Sat Sep 13, 2008 9:47 am

I'd love to hear how a test like that turns out.

You never know....

Kayak Jack · Post by **Kayak Jack** » Sat Sep 13, 2008 10:41 am

From my days (about 60 years ago) of building model airplanes - balsa is THIRSTY when it gets around glue. Your weight difference may more than disappear - but your wallet will get lighter from buying more epoxy.

I'd try some tests on smaller chunks before I started a big project. Use same-sized pieces of good plywood, foam, and balsa, and test for puncture resistance and break strength. Then, with a duplicate set, epoxy each one, and glass each exactly the same, then test again for puncture resistance and break strength. I think we all would be interested in the results. (I', holding my breath - so please don't dally too long, or I may........)

Finding a karate guy to whack them while they lay across two cement blocks may be your toughest part of this assignment?

Oldsparkey · Post by **Oldsparkey** » Sat Sep 13, 2008 10:47 am

jlparsons...

Boy .. I'm glad you mentioned the balsa as the core wood , I have been thinking about that for a long time.
The thing that stopped me was the cost of the wood , if it can be located. Locating a couple 4 x 8 sheets here in Florida is next to impossible unless I wanted it shipped in from Australian or South America and that cost was something beyond what I was willing to do.

Chuck.

Kayak Jack · Post by **Kayak Jack** » Sat Sep 13, 2008 10:49 am

I've never seen a 4' X 8' sheet of balsa, nor even heard of it. Wow! Can't weigh more than a very few pounds.

jlparsons · Post by **jlparsons** » Sat Sep 13, 2008 12:03 pm

I've thunk on this all morning and the decisive question is this - how thick a covering of glass is required over balsa before it's puncture resistance becomes acceptable?

This would actually be pretty easy to test. You need a measurable impact, like dropping something that will hit in a predictable way from a set height (lead ball?). Use this to test the glass-on-ply that we all know and love and remember the height you had to drop it from to break the glass. Then take a thick balsa plank and glass it on one side from end to end such that you have sections with 1, 2, 3, 4, 5 layers etc from one end to the other. Then perform the impact test again on each section of the plank and see which number of glass layers gives a result closest to the ply. Once you know how much glass is needed, you can then work out the weight advantage (or otherwise) of building a boat like this.

I discovered you can get balsa plywood, which surprised me. http://www.specializedbalsa.com/balsa_plywood.php

This is that 12lb balsa strip built canoe - http://www.storerboatplans.com/Balsacan ... canoe.html