Thread: Paulownia timber for strip planking

Thanks Mark.
We know about Whitewood.
What we probably didn't know is the relevant numbers relating to the timber.
(I certainly didn't)
So a special thank-you for doing the number-crunching & advising us the results.

cheers
AJ

And the big question - where would you use Paulonia in your boat?
Anywhere that specifies a softwood?
Replace Oregon with Paulonia?
Stringers? Laminated stem? Inwales? Gunwales? Oars? Spars? That funny stick like thing that keeps jabbing you in the ribs?

Serious Mark, these are questions that have not been answered, just hinted at.

Richard

I am not a technical person and appreciate the plug Mark gave my small business and Australian paulownia. I will not sell paulownia to any one (for any purpose) unless I know the end use and I'm satisfied that it is a suitable timber for that purpose. I did not sell it to a customer who wanted to build a mast etc. It was a Michael Storer design and I asked him to OK it first. Michael didn't.

A simple rule, supported by Michael, is use paulownia anywhere you could/would use Western Red Cedar. Anywhere else is at the builders own risk if he is going all out to reduce weight. Michael discussed this point in the forum some time ago. Risk versus performance.

I have been telling customers that importerd Chinese paulownia is not as good as the Australian. It's comforting to know that some one did proper testing and proved it. It's good to get away from the 'gut feeling' assessment that end users have told me and have something concrete to base my future comments.

John

Mark,

Plus 1 for AJ's comments.

Would like to see the numbers if that's possible, just as a summary table. I understand there may be legal or confidentiality reasons why this can't be done but is there any chance of you putting them up on your website, please?

Also, was there a corresponding difference in density? Just wondering if Paulownia deviates from the general trend of stronger = heavier as it matures.

Thanks again for the post.

where would you use Paulonia in your boat?
Anywhere that specifies a softwood?
Replace Oregon with Paulonia?
Stringers? Laminated stem? Inwales? Gunwales? Oars? Spars? That funny stick like thing that keeps jabbing you in the ribs?

You need to be careful in this regard. This is a pretty broad question. Would I replace Oregon with Paulonia.. No. Oregan had 4 times the strength. As an example lets use a 14 ft boat with frame spacings of 21 inches (533mm) and lets keep this simple.

With Oregon:
the frame siding and molding would need to be .75" (19mm) by 1.8in (45mm)

With Chinese Paulownia keeping the same 19mm thickness, the molding would need to be 2.9in (73mm) to take the same load. Big difference.

Now, the big question is; what is the purpose of the boat. If its a simple little dinghy for playing around lakes/ rivers then we can reduce our scantling because our safety factors need not be so high or our panel deflection limits. (ie no slamming waves etc as experienced outside)
So in this regard, we could reduce our frame molding to 2.3 inches(58mm). However, if your intension is to take it outside, using the 2.3"or 58mm, then expect the possibility of frame cracking pending the conditions your out in.

Use paulownia anywhere you could/would use Western Red Cedar

Be very careful. If the boat is designed and engineered for Paulownia and you opt for WRC, you'll only end up with a stronger boat. If however its reversed...Whoops, you could end up in trouble
Now, the above is pretty broad strokes as it depends on the boat hull shape/ service intended/ where it will be used/ frame spacings/ stringer spacings/ laminate schedule... its not just a simple swap and go.

Now some of you may have already swaped and found it ok. For me I need to know absolutley as its my neck on the line. and I don't like throwing darts at a board.

Just a comment
regards
Mark

G'day Labr@

Also, was there a corresponding difference in density? Just wondering if Paulownia deviates from the general trend of stronger = heavier as it matures.

Yes, in regards to Density, there was a difference.
Chinese Paulownia = 290 kg/m^3
Qld/NSW Paulownia = 270 kg/m^3

What's interesting is WA Paulownia is 330 kg/M^3.

Would like to see the numbers if that's possible, just as a summary table. I understand there may be legal or confidentiality reasons why this can't be done but is there any chance of you putting them up on your website, please?

Sorry Mate, can't do. At $7000 for the tests, It's something one is not going to just give away freely.
However, I hope the above gives an indication.

In relation to the above example of using a frame, I thought I'd just clarify something here. These calcs are based solely on the timber itself. No epoxy or tabbing laminates...nothing but the timber. The minute we begin to add filleting and tabbing and other laminate schedules, the whole thing changes as now the lamintate becomes the dominating factor and not the timber. Being that E-Glass is so much stronger, the siding and molding of the timber can be vastly reduced as it's strengths does not come into the calculation, only its core shear strength. Now it becomes a different calculation entirely. I just gave the above example just to show what "can " happen.

regards
Mark

"Yes, in regards to Density, there was a difference.
Chinese Paulownia = 290 kg/m^3
Qld/NSW Paulownia = 270 kg/m^3

What's interesting is WA Paulownia is 330 kg/M^3. "

Wouldn't this be more to do with the moisture content in the timber . I know that the timber from Coffs Harbour is kiln dried to 11% and this could account for the lower density.
Whitewood

In regards to strength, the Chinese Paulownia is only 3/4's the strength of the Qld paulownia. in regards to moisture content, the chinese version was also tested at 11% as well. I recently got Chuck from Duckworks onto this as well. He was astounded with the samples he recieved from the US Paulownia supplier. He's never seen anything like it. Its great stuff to work with compared the WRC

Originally Posted by Mark Bowdidge

Sorry Mate, can't do. At $7000 for the tests, It's something one is not going to just give away freely.

I half expected something of the sort so it's all good . Still appreciate the info given.

Must say I expected the Chinese stuff to be lower density but wasn't sure by how much - when I read the actual result it was a moment! Means the Qld timber has much better strength to weight ratio than you would guess from just the strength figures.

I don't know if any of you guys have been following my thread but I got my Paulownia from John...right great gentleman and all. My Tomcat is planked with 12mm from John - beautiful to work but keep your tools sharp. To be sure I have laminated the outside with Biax 12oz cloth and will do the same inside after turnaover.

Will also reduce the number of internal frames by half the number using this construction method.

As an aside John supplies from his own plantation as well as the other.

I'll add m2cw to say John is extremely helpful, freight is not as expensive as you might think and it comes packed with special care thanks John.

The thing I have found being especially soft it does crush easily so a bit of care and thought in where and how it is used is needed but it is nice to work and light.

Mike

Speaking with Dave (Port Phillip Plantation Shutters - Melbourne) the other day, I queryed the structure of the tree. As it turns out, the species is actually related to Bamboo.

Unlike normal typical trees where they have an open cell stucture, Paulownia is a "closed cell" tree and therefore is similiar to foam core. He then told me a story of one of his boatbuilding clients who actually submerged a piece of Paulownia is his pool under a brick and then after a month, pulled it out, weighed and cut the timber in half to check how much water the timber had obsorbed. Nothing.

Hmmm...This is an experiment I'd actually love to try for myself.
regards
Mark

That is interesting and may explain why it tends to fracture straight across the section with little splitting, in my experience anyway.

As I understand it, 'closed cell structure' is one of the traditional definitions of a 'hardwood' (many of which aren't hard at all), and it explains how Balsa can be classified as one, despite its obvious softness.