This was a discussion about what materials were appropriate if building a wooden canoe in Australia.
In the 1970s and ’80s there were huge amounts of Douglas Fir (locally called “Oregon”) and Western Red Cedar brought in to build houses.
This has declined markedly turning these materials into premium timbers.
However, plantation grown Paulownia, a light Chinese timber is cheap compared to other alternatives.
This post is from our very early experience with Paulownia in the 1990s.
It is also increasingly available throughout the USA, Canada and Europe. It is often used for window shutters and for wooden surfboards.
Thickness of strips if building of Paulownia and discussion of planning timber colour layout
Originally Posted by Ramps
And yes the timber I bought the other day is Paulownia.
I was rather pleasantly surprised when I went to pick it up thinking it would look as boring as Balsa.
Sorry Mik no ofense meant as your Balsa Wee Lassie does look wonderful and it was what sold me on Paulownia, thinking if you could make Balsa look great then I couldn’t go worse with Paulownia. Looks a fair bit like Tassy Oak/Vic Ash if you ask me.
I am keen to hear how the Paulownia goes. There is a bit on the net and other places suggesting that because of the lower strength compared to Cedar that the Paulownia strips need to be thicker.
Don’t be swayed – use at the same thickness as cedar (6mm) and save a bit more weight. The balsa canoe with 6mm hull and much lighter glass than you will be using was plenty strong enough.
My take is that it is the timber that gives the boat its strength and the glass that stops the timber from denting.
This is a practical view only. The engineeering view (ie the correct one) is that the glass gives the timber cross grain strength (its real function) but the 0.75oz glass that I used proved adequate for that purpose.
Light glass on Paulownia canoe at Duck Flat Wooden Boats Autumn School.
So if a very light glass gives enough cross grain strength – if follows that heavier glass fulfills a different function – which is to protect the timber from denting in contact with stones or snags. Usually it is land based damage.
So what did I get away with building a balsa strip canoe?
My mindset was to push the weight down as much as possible and think of it as a disposable boat.
With a bit of care it was amazingly robust and it looked great after three years of use. Sold on to a new owner.
It is a great example of how far it is possible to go in weight saving.
A common mindset is to try and reduce weight by making the timber thinner.
This is daft because the stiffness of the structure depends on the timber thickness. AND THE TIMBER IS THE LIGHTEST COMPONENT!
So the best sense is to reduce the amount of high density glass and reduce the timber DENSITY while retaining thickness.
For this Balsa or Paulownia is ideal.
Back to Paulownia
Keep the gunwale trim keel and perhaps external stem in contrasting colour and it will be just gorgeous.
BTW the Balsa Canoe was even more gorgeous in the flesh than the photos show – I’ll have nothing said against balsa from a decorative point of view!!! In a way I think the hull timber is irrelevant – it is the trim that gives you the shape of the boat so that should be really pretty (I found some Australian Red Cedar for my tiny gunwales and inwales.)
Yep – I thought the Balsa looked like Tassie Oak at the time too!!!
There are a couple of little tricks as far as setting of gunwales too which I might tell you later if you are interested – I’m off to the city.
Keeping the weight down by choosing low density timbers
I am thinking a bit of Jarrah for Gunwale, trim and stem (outer) is that overboard (sorry no pun intended). Do I need the strength for the inner stems or will a bit more paulownia do?
Would love Aust Red Cedar but it seems a little hard to get hold of at the moment.
Jarrah is the right colour but is WAY too heavy for a boat of this style. The boats breathe lightness. Would be a pity to bog it down. Because the boat is so light you don’t need the strength and toughness of the Jarrah anywhere really. If hit the boat is light enough to move out of the way to some extent.
Jarrah would be for the keel though – but keep the dimensions down to the minimum suggested in Canoecraft (or less) Have a look at the Balsa Canoe page to see how little you can get away with. Though gunwales and inwales I would stick to Canoecraft’s suggestions or a little less.
What I sometimes do when I want to keep bits of the boat light is to use the lightest wood I can find for bits that are going to take some abrasion (eg external keels, skegs, bottom runners) but cap them with a 6mm strip of something like Jarrah. Not much extra weight but you get the full benefit of the tougher wood. When it becomes too damaged plane it off and put a new Jarrah strip along the edge.
What weight of glass to use on a strip plank canoe
One more question to do with construction … and I know the debates been on for years but … what would you recommend for a family based canoe, like this, for f’glass … 6 oz both inner and outer or 4 oz inner, 6 outer or an extra layer along the keel … I’ve heard all these (plus more) recommendations.
I generally use 6oz because it is readily available. But would probably recommend 4 for a canoe.
Or i would have no worries about using 0.75 (though it would need to be doubled in the bottom of the cockpit and the areas of the bottom on the outside that might contact the ground.
That worked very well for the more vulnerable Balsa Canoe. So it depends on how far you want to go.
My feeling is that most recommendations simply express personal biases rather than any sort of firm fact – generally if a single facet answer is being offered it is opinion.
6oz will resist denting quite well, 4oz will still be fine. 0.75 with two layers in vulnerable areas and you have to start putting the boat down on the ground upside down so that stones don’t dent the bottom – though Paulownia would be much more resistant than balsa!!!
The thing to be very aware of is the lighter the boat the less you need to protect it.
With the Balsa Canoe, which I expected to fall apart in a couple of years of use, I sold it after three years for the best profit I have ever made on a boat sail. Thanks Leigh Hemmings for brokering the deal!
Pretty as a picture.
Paulownia for Timber work. Gunwales, inwales, framing, cleats, stem, deckclamps and beams
I have two examples of using Paulownia use for the solid timber parts of boats.
The 16ft Eureka Canoe built to a weight of 15kg or 34lbs. Most of the timberwork was Paulownia. Hull was 4mm ply with some very light 2oz fibreglass over some of the bottom area and floor area.
Goat Island Skiff built by Bruce Taylor had most of the solid timber in Paulownia. The normal Goat Island Skiff weight using Western Red Cedar and Douglas Fir (Oregon) for the timberwork is around 130lbs. Bruce’s GIS was 105lbs. A saving of 25lbs or 12kg. The light Paulownia was protected by cappings of hardwood for the bottom runners and gunwales as can be seen above.